## A01-Research Projects

### Paper | Original Paper

#### 2017

Tomoyuki Mano, *Jean-Baptiste Delfau, Junichiro Iwasawa, and Masaki Sano,
Optimal run-and-tumble based transportation of a Janus particle with active steering,
Proceedings of the National Academy of Sciences 114, in press.

[Summary] Commanding the swimming of micrometric objects subjected to thermal agitation is always challenging both for artificial and living systems. Now, artificial swimmers can be designed whose self-propelling force can be tuned at will. However, orienting such small particles to an arbitrary direction requires counterbalancing the random rotational diffusion. Here, we introduce a simple concept to reorient artificial swimmers, granting them a motion similar to the run-and-tumbling behavior of Escherichia coli. We demonstrate it using Janus particles with asymmetric surface coating and moving under an AC electric field. Moreover, we determine the optimal strategy and compare it with biological swimmers. Our results encourage further investigation into dynamical behavior of colloidal particles, as well as application to microscopic devices.

*Yohsuke T. Fukai and Kazumasa A. Takeuchi,
Kardar-Parisi-Zhang Interfaces with Inward Growth,
Physical Review Letters 119, 030602/1-5 (2017).

[Summary] We study the (1+1)-dimensional Kardar-Parisi-Zhang (KPZ) interfaces growing inward from ring-shaped initial conditions, experimentally and numerically, using growth of a turbulent state in liquid-crystal electroconvection and an off-lattice Eden model, respectively. To realize the ring initial condition experimentally, we introduce a holography-based technique that allows us to design the initial condition arbitrarily. Then, we find that fluctuation properties of ingrowing circular interfaces are distinct from those for the curved or circular KPZ subclass and, instead, are characterized by the flat subclass. More precisely, we find an asymptotic approach to the Tracy-Widom distribution for the Gaussian orthogonal ensemble and the Airy1 spatial correlation, as long as time is much shorter than the characteristic time determined by the initial curvature. Near this characteristic time, deviation from the flat KPZ subclass is found, which can be explained in terms of the correlation length and the circumference. Our results indicate that the sign of the initial curvature has a crucial role in determining the universal distribution and correlation functions of the KPZ class.

Kazumasa A. Takeuchi,
1/fα power spectrum in the Kardar-Parisi-Zhang universality class,
Journal of Physics A: Mathematical and Theoretical 50, 264006/1-17 (2017).

[Summary] The power spectrum of interface fluctuations in the (1+1)-dimensional Kardar-Parisi-Zhang (KPZ) universality class is studied both experimentally and numerically. A 1/f-type spectrum is found and characterized through a set of 'critical exponents' for the power spectrum. The recently formulated aging Wiener-Khinchin theorem accounts for the observed exponents. Interestingly, the 1/f-type spectrum in the KPZ class turns out to contain information on a universal distribution function characterizing the asymptotic state of the KPZ interfaces, namely the Baik-Rains universal variance. It is indeed observed in the presented data, both experimental and numerical, and in both circular and flat interfaces in the long time limit.

*Yuliang Jin, Hajime Yoshino,
Exploring the complex free energy landscape of the simplest glass by rheology,
Nature Communications 8, 14935 (2017).

[Summary] For amorphous solids, it has been intensely debated whether the traditional view on solids, in terms of the ground state and harmonic low energy excitations on top of it, such as phonons, is still valid. Recent theoretical developments of amorphous solids revealed the possibility of unexpectedly complex free energy landscapes where the simple harmonic picture breaks down. Here we demonstrate that standard rheo- logical techniques can be used as powerful tools to examine non-trivial consequences of such complex free energy landscapes. By extensive numerical simulations on a hard sphere glass under quasi-static shear at finite temperatures, we show that, above the so-called Gardner transition density, the elasticity breaks down, the stress relax- ation exhibits slow and aging dynamics, and the apparent shear modulus becomes protocol-dependent. Being designed to be reproducible in laboratories, our approach may trigger explorations of the complex free energy landscapes of a large variety of amorphous materials.

*Jacopo De Nardis, Pierre Le Doussal, and Kazumasa A. Takeuchi,
Memory and Universality in Interface Growth,
Physical Review Letters 118, 125701/1-5 (2017).

[Summary] Recently, very robust universal properties have been shown to arise in one-dimensional growth processes with local stochastic rules, leading to the Kardar-Parisi-Zhang (KPZ) universality class. Yet it has remained essentially unknown how fluctuations in these systems correlate at different times. Here, we derive quantitative predictions for the universal form of the two-time aging dynamics of growing interfaces and we show from first principles the breaking of ergodicity that the KPZ time evolution exhibits. We provide corroborating experimental observations on a turbulent liquid crystal system, as well as a numerical simulation of the Eden model, and we demonstrate the universality of our predictions. These results may give insight into memory effects in a broader class of far-from-equilibrium systems.

*Ｍasahiko Ueda, Shin-ichi Sasa,
Replica symmetry breaking in trajectory space for the trap model,
Journal of Physics A: Mathematical and Theoretical 50, 125001/1-14 (2017).

[Summary] We study the localization in the one-dimensional trap model in terms of statistical mechanics of trajectories. By numerically investigating overlap between trajectories of two particles on a common disordered potential, we find that there is a phase transition in the path ensemble. We characterize the low temperature phase as a replica symmetry breaking phase in trajectory space.

*Masato Itami, Shin-ichi Sasa,
Universal Form of Stochastic Evolution for Slow Variables in Equilibrium Systems,
Journal of Statistical Physics 167, 46-63 (2017).

[Summary] Nonlinear, multiplicative Langevin equations for a complete set of slow variables in equilibrium systems are generally derived on the basis of the separation of time scales. The form of the equations is universal and equivalent to that obtained by Green. An equation with a nonlinear friction term for Brownian motion turns out to be an example of the general results. A key method in our derivation is to use different discretization schemes in a path integral formulation and the corresponding Langevin equation, which also leads to a consistent understanding of apparently different expressions for the path integral in previous studies.

*Daiki Nishiguchi, Ken H. Nagai, Hugues Chate, and Masaki Sano,
Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria,
Physical Review E 95, 020601(R) /1-6 (2017).

[Summary] We study the collective dynamics of elongated swimmers in a very thin fluid layer by devising long, filamentous, non-tumbling bacteria. The strong confinement induces weak nematic alignment upon collision, which, for large enough density of cells, gives rise to global nematic order.　This homogeneous but fluctuating phase, observed on the largest experimentally-accessible scale of millimeters,　 exhibits the properties predicted by standard models for flocking such as the Vicsek-style model of polar particles 　with nematic alignment: true long-range nematic order and non-trivial giant number fluctuations.

Harukuni Ikeda, Kunimasa Miyazaki and *Giulio Biroli,
The Fredrickson-Anderson model with random pinning on Bethe lattices and its MCT transitions,
EPL 116, 56004/1-8 (2017).

[Summary] We investigate the dynamics of the randomly pinned Fredrickson-Andersen modelon the Bethe lattice. We find a line of random pinning dynamical transitions whose dynamicalcritical properties are in the same universality class of the A2 and A3 transitions of the modecoupling theory. The A3 behavior appears at the terminal point, where the relaxation becomeslogarithmic and the relaxation time diverges exponentially. We explain the critical behavior in terms of self-induced disorder and avalanches, strengthening the relationship discussed in recent works between glassy dynamics and random field Ising model.

#### 2016

Gioia Carinci, Cristiana Giardina, Frank Redig, Tomohiro Sasamoto,
A generalized asymmetric exclusion process with Uq(sl2) stochastic duality,
Probability Theory and Related Fields 166(3), 887-933 (2016).

[Summary] In the studies of one-dimensional asymmetric simple exclusion process(ASEP), the existence of self-duality is very useful but it has not been well understood what type of stochastic models with current have self-duality. In this paper we present a general scheme to construct stochastic processes with self-duality related to quantum group symmetries. As an example we constructed a model with multi-particle occupancy at a site related to higher spin representation of the quantum algebra Uq(sl2).

*Harukuni Ikeda, Kunimasa Miyazaki, and *Atsushi Ikeda,
A note on the replica liquid theory of binary mixtures,
Journal of Chemical Physics 145, 216101/1-2 (2016).

[Summary] We reformulate the Replica Liquid Theory in order to resolve the inherent problem related to the configurational entropy of the supercooled binary systems near the glass transition. By rewriting generating functions using the Morita-Hiroike representation, we have shown that the configurational entropy correctly converges to that of monatomic system in this limit.

*Shumpei Yamamoto, Sosuke Ito, Naoto Shiraishi, and Takahiro Sagawa,
Linear irreversible thermodynamics and Onsager reciprocity for information-driven engines,
Phyical Review E 94, 052121/1-11 (2016).

[Summary] In the recent progress in nonequilibrium thermodynamics, information has been recognized as a kind of thermodynamic resource that can drive thermodynamic current without any direct energy injection. In this paper, we establish the framework of linear irreversible thermodynamics for a broad class of autonomous information processing. In particular, we prove that the Onsager reciprocity holds true with information: The linear response matrix is well-defined and is shown symmetric with both of the information affinity and the conventional thermodynamic affinity. As an application, we derive a universal bound for the efficiency at maximum power for information-driven engines in the linear regime. Our result reveals the fundamental role of information flow in linear irreversible thermodynamics.

Naoto Shiraishi, Keiji Saito and Hal Tasaki,
Universal trade-off relation between power and efficiency for heat engines,
Physical Review Letters 117, 190601/1-5 (2016).

[Summary] For a general thermodynamic system described as a Markov process, we prove a general lower bound for dissipation in terms of the square of the heat current, thus establishing that nonvanishing current inevitably implies dissipation. This leads to a universal trade-off relation between efficiency and power, with which we rigorously prove that a heat engine with nonvanishing power never attains the Carnot efficiency. Our theory applies to systems arbitrarily far from equilibrium, and does not assume any specific symmetry of the model.

Takuma Akimoto, Eli Barkai, Keiji Saito,
Universal Fluctuations of Single-Particle Diffusivity in Quenched Environment,
Physical Review Letters 117, 180602 (2016).

[Summary] Local diffusion coefficients in disordered materials such as living cells are highly heterogeneous. We consider finite systems with quenched disorder in order to investigate the effects of sample disorder fluctuations and confinement on single-particle diffusivity. While the system is ergodic in a single disorder realization, the time-averaged mean square displacement depends crucially on the disorder; i.e., the system is ergodic but non-self-averaging. Moreover, we show that the disorder average of the time-averaged mean square displacement decreases with the system size. We find a universal distribution for diffusivity in the sense that the shape of the distribution does not depend on the dimension. Quantifying the degree of the non-self-averaging effect, we show that fluctuations of single-particle diffusivity far exceed the corresponding annealed theory and also find confinement effects. The relevance for experimental situations is also discussed.

Ryoji Miyazaki, Takeshi Kawasaki, and *Kunimasa Miyazaki,
Cluster Glass Transition of Ultrasoft-Potential Fluids at High Density,
Physical Review Letterrs 117, 165701/1-5 (2016).

[Summary] Using molecular dynamics simulation, we investigate the slow dynamics of a supercooled binarymixture of soft particles interacting with a generalized Hertzian potential. At low density, it displays typicalslow dynamics near its glass transition temperature. At higher densities, particles bond together, formingclusters, and the clusters undergo the glass transition. The number of particles in a cluster increases one byone as the density increases. We demonstrate that there exist multiple cluster-glass phases characterized bya different number of particles per cluster, each of which is separated by distinct minima. Surprisingly, a socalledhigher order singularity of the mode-coupling theory signaled by a logarithmic relaxation is observedin the vicinity of the boundaries between monomer and cluster glass phases. The system also exhibits richand anomalous dynamics in the cluster glass phases, such as the decoupling of the self- and collectivedynamics.

Daijyu Nakayama, Hajime Yoshino, Francesco Zamponi,
Protocol-dependent shear modulus of amorphous solids,
Journal of Statistical Mechanics: Theory and Experiment 10, 104001 (2016).

We investigate the linear elastic response of amorphous solids to a shear strain at zero temperature. We find that the response is characterized by at least two distinct shear moduli. The first one, πZFC, is associated with the linear response of a single energy minimum. The second, πFC, is related to sampling, through plastic events, an ensemble of distinct energy minima. We provide examples of protocols that allow one to measure both shear moduli. In agreement with a theoretical prediction based on the exact solution in infinite spatial dimensions, the ratio πFC/πZFC is found to vanish proportionally to the square root of pressure at the jamming transition. Our results establish that amorphous solids are characterized by a rugged energy landscape, which has a deep impact on their elastic response, as suggested by the infinite-dimensional solution.

Yoshimichi Teratani, Rui Sakano, Ryo Fujiwara, Tokuro Hata, Tomonori Arakawa, Meydi Ferrier, Kensuke Kobayashi and Akira Oguri,
Field-enhanced Kondo correlations in a half-filling nanotube dot: evolution of an SU(n) Fermi-liquid fixed point,
Journal of the Physical Society of Japan 85, 094718/1-18 (2016).

[Summary] Carbon nanotube quantum dot has four-fold degenerate one-particle levels, which bring a variety to the Kondo effects taking place in a wide tunable-parameter space. We theoretically study an emergent SU(2) symmetry that is suggested by recent magneto-transport measurements, carried out near two electrons filling. It does not couple with the magnetic field, and emerges in the case where the spin and orbital Zeeman splittings cancel each other out in two of the oneparticle levels among four. This situation seems to be realized in the recent experiment. Using the Wilson numerical renormalization group, we show that a crossover from the SU(4) to SU(2) Fermi-liquid behavior occurs as magnetic field increases at two impurity-electrons filling. We also find that the quasiparticles are significantly renormalized as the remaining two one-particle levels move away from the Fermi level and are frozen at high magnetic fields. Furthermore, we consider how the singlet ground state evolves during such a crossover. Specifically, we reexamine the SU(N) Kondo singlet for M impurity-electrons filling in the limit of strong exchange interactions. We find that the nondegenerate Fermi-liquid fixed point of Nozieres and Blandin can be described as abosonic Perron-Frobenius vector for M composite pairs, each of which consists of one impurity-electron and one conduction-hole. This interpretation in terms of the Perron-Frobenius theorem can also be extended to the Fermi-liquid fixed-point without the SU(N) symmetry.

Yoshiyuki Chiba and *Naoko Nakagawa,
Numerical determination of entropy associated with excess heat in steady-state thermodynamics,
Physical Review E 94, 022115/1-10 (2016).

[Summary] We numerically determine the global entropy for heat-conducting states, which is connected to the so-called excess heat considered as a basic quantity for steady-state thermodynamics in nonequilibrium. We adopt an efficient method to estimate the global entropy from the bare heat current and find that the obtained entropy agrees with the familiar local equilibrium hypothesis well. Our method possesses a wider applicability than local equilibrium and opens a possibility to compare thermodynamic properties of complex systems in nonequilibrium with those in the local equilibrium. We further investigate the global entropy for heat-conducting states and find that it exhibits both extensive and additive properties; however, the two properties do not degenerate each other differently from those at equilibrium. The separation of the extensivity and additivity makes it difficult to apply powerful thermodynamic methods to the nonequilibrium steady states.

Shou-Wen Wang, Kyogo Kawaguchi, Shin-ichi Sasa, and Lei-Han Tang,
Entropy Production of Nanosystems with Time Scale Separation,
Physical Review Letters 117, 070601/1-070601-5 (2016).

[Summary] Energy flows in biomolecular motors and machines are vital to their function. Yet experimental observations are often limited to a small subset of variables that participate in energy transport and dissipation. Here we show, through a solvable Langevin model, that the seemingly hidden entropy production is measurable through the violation spectrum of the fluctuation-response relation of a slow observable. For general Markov systems with time scale separation, we prove that the violation spectrum exhibits a characteristic plateau in the intermediate frequency region. Despite its vanishing height, the plateau can account for energy dissipation over a broad time scale. Our findings suggest a general possibility to probe hidden entropy production in nanosystems without direct observation of fast variables.

*Kazumasa A. Takeuchi and Takuma Akimoto,
Characteristic Sign Renewals of Kardar-Parisi-Zhang Fluctuations,
Journal of Statistical Physics 164, 1167-1182 (2016).

[Summary] Tracking the sign of fluctuations governed by the (1+1)-dimensional Kardar-Parisi-Zhang (KPZ) universality class, we show, both experimentally and numerically, that its evolution has an unexpected link to a simple stochastic model called the renewal process, studied in the context of aging and ergodicity breaking. Although KPZ and the renewal process are fundamentally different in many aspects, we find remarkable agreement in some of the time correlation properties, such as the recurrence time distributions and the persistence probability, while the two systems can be different in other properties. Moreover, we find inequivalence between long-time and ensemble averages in the fraction of time occupied by a specific sign of the KPZ-class fluctuations. The distribution of its long-time average converges to nontrivial broad functions, which are found to differ significantly from that of the renewal process, but instead be characteristic of KPZ. Thus, we obtain a new type of ergodicity breaking for such systems with many-body interactions. Our analysis also detects qualitative differences in time-correlation properties of circular and flat KPZ-class interfaces, which were suggested from previous experiments and simulations but still remain theoretically unexplained.

Johannes Stigloher, Martin Decker, Helmut S. Körner, Kenji Tanabe, Takahiro Moriyama, Takuya Taniguchi, Hiroshi Hata, Marco Madami, Gianluca Gubbiotti, Kensuke Kobayashi, Teruo Ono, and Christian H. Back,
Snell’s Law for Spin Waves,
Physical Review Letters 117, 037204/1-4 (2016).

[Summary] We report the experimental observation of Snell’s law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. We use a thickness step as the interface between two media with different dispersion relations. Since the dispersion relation for magnetostatic waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snell's law known in optics are observed for incidence angles larger than 25° with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.

*Xiong Ding, Hugues Chate, Predrag Cvitanovic, Evangelos Siminos, and Kazumasa A. Takeuchi,
Estimating the Dimension of an Inertial Manifold from Unstable Periodic Orbits,
Physical Review Letters 117, 024101/1-5 (2016).

[Summary] We provide numerical evidence that a finite-dimensional inertial manifold on which the dynamics of a chaotic dissipative dynamical system lives can be constructed solely from the knowledge of a set of unstable periodic orbits. In particular, we determine the dimension of the inertial manifold for the Kuramoto-Sivashinsky system and find it to be equal to the “physical dimension” computed previously via the hyperbolicity properties of covariant Lyapunov vectors.

Misaki Ozawa, Kang Kim, *Kunimasa Miyazaki,
Tuning Pairwise Potential Can Control the Fragility of Glass-Forming Liquids: From Tetrahedral Network to Isotropic Soft Sphere Models,
Journal of Statistical Mechanics: Theory and Experiment None, 074002/1-21 (2016).

[Summary] We perform molecular dynamics simulations for a SiO2 glass formermodel proposed by Coslovich and Pastore (CP) over a wide range of densities. Thedensity variation can be mapped onto the change of the potential depth between Siand O interactions of the CP model. By reducing the potential depth (or increasingthe density), the anisotropic tetrahedral network structure observed in the originalCP model transforms into the isotropic structure with the purely repulsive softspherepotential. Correspondingly, the temperature dependence of the relaxationtime exhibits the crossover from Arrhenius to super-Arrhenius behavior. Beingable to control the fragility over a wide range by tuning the potential of a singlemodel system helps us to bridge the gap between the network and isotropic glassformers and to obtain the insight into the underlying mechanism of the fragility. We study the relationship between the fragility and dynamical properties such as the magnitude of the Stokes–Einstein violation and the stretch exponent in the density correlation function. We also demonstrate that the peak of the specific heat systematically shifts as the density increases, hinting that the fragility is correlated with the hidden thermodynamic anomalies of the system.

Keiji Saito and Abhishek Dhar,
Waiting for rare entropic fluctuations,
Europhys Letters 114, 50004/1-6 (2016).

[Summary] Nonequilibrium fluctuations of various stochastic variables, such as work and entropy production, have been widely discussed recently in the context of large deviations, cumulants and fluctuation relations. Typically one looks at the probability distributions for entropic fluctuations of various sizes to occur in a fixed time interval. An important and natural question is to ask for the time one has to wait to see fluctuations of a desired size. We address this question by studying the first-passage time distribution (FPTD). We derive the general basic equation to get the FPTD for entropic variables. Based on this, the FPTD on entropy production in a driven colloidal particle in the ring geometry is illustrated. A general asymptotic form of the FPTD and integral fluctuation relation symmetry in terms of the first passages are found.

*J.-B. Delfau, John J. Molina and M. Sano,
Collective behavior of strongly confined suspensions of squirmers,
Europhysics Letters 114, 24001/1-5 (2016).

[Summary] We run numerical simulations of strongly confined suspensions of model spherical swimmers called “squirmers”. Because of the confinement, the Stokeslet dipoles generated by the particles are quickly screened and the far-field flow is dominated by the source dipole for all the different kinds of squirmers. However, we show that the collective behavior of the suspension still depends on the self-propelling mechanism of the swimmers as polar states can only be observed for neutral squirmers. We demonstrate that the near-field hydrodynamic interactions play a crucial role in the alignment of the orientation vectors of spherical particles. Moreover, we point out thatthe enstrophy and the fluid fluctuations of an active suspension also depend on the nature of the squirmers.

Tatsuya Muro, Yoshitaka Nishihara, Shota Norimoto, Meydi Ferrier, Tomonori Arakawa, *Kensuke Kobayashi, Thomas Ihn, Clemens Rösler, Klaus Ensslin, Christian Reichl, and Werner Wegscheider,
Finite shot noise and electron heating at quantized conductance in high-mobility quantum point contacts,
Physical Review B 93, 195411/1-7 (2016).

[Summary] We report a precise experimental study on the shot noise of a quantum point contact (QPC) fabricated in a GaAs/AlGaAs based high-mobility two-dimensional electron gas (2DEG). The combination of unprecedented cleanliness and very high measurement accuracy has enabled us to discuss the Fano factor to characterize the shot noise with a precision of 0.01. We observed that the shot noise at zero magnetic field exhibits a slight enhancement exceeding the single particle theoretical prediction, and that it gradually decreases as a perpendicular magnetic field is applied. We also confirmed that this additional noise completely vanishes in the quantum Hall regime. These phenomena can be explained by the electron heating effect near the QPC, which is suppressed with increasing magnetic field.

Shin-ichi Sasa, Yuki Yokokura,
Thermodynamic entropy as a Noether invariant,
Physical Review Letters 116, 140601/1-140601/6 (2016).

[Summary] We study a classical many-particle system with an external control represented by a time-dependent extensive parameter in a Lagrangian. We show that thermodynamic entropy of the system is uniquely characterized as the Noether invariant associated with a symmetry for an infinitesimal nonuniform time translation t→t+ηℏβ, where η is a small parameter, ℏ is the Planck constant, β is the inverse temperature that depends on the energy and control parameter, and trajectories in the phase space are restricted to those consistent with quasistatic processes in thermodynamics.

Daniele Coslovich, *Atsushi Ikeda, Kunimasa Miyazaki,
Mean-field dynamic criticality and geometric transition in the Gaussian core model,
Physical Review E 93, 042602/1-8 (2016).

[Summary] We use molecular dynamics simulations to investigate dynamic heterogeneities and the potential energy landscape of the Gaussian core model (GCM). Despite the nearly Gaussian statistics of particles' displacements, the GCM exhibits giant dynamic heterogeneities close to the dynamic transition temperature. The divergence of the four-point susceptibility is quantitatively well described by the inhomogeneous version of the mode-coupling theory. Furthermore, the potential energy landscape of the GCM is characterized by large energy barriers, as expected from the lack of activated, hopping dynamics, and display features compatible with a geometric transition. These observations demonstrate that all major features of mean-field dynamic criticality can be observed in a physically sound, three-dimensional model.

*Takao Ohta, Mitsusuke Tarama and Masaki Sano,
Simple model of cell crawling,
Physica D 318, 3-11 (2016).

[Summary] Based on symmetry consideration of migration and shape deformations, we formulate phenomenologically the dynamics of cell crawling in two dimensions. Forces are introduced to change the cell shape. The shape deformations induce migration of the cell on a substrate. For time-independent forces we show that not only a stationary motion but also a limit cycle oscillation of the migration velocity and the shape occurs as a result of nonlinear coupling between different deformation modes. Time-dependent forces are generated in a stochastic manner by utilizing the so-called coherence resonance of an excitable system. The present coarse-grained model has a flexibility that it can be applied, e.g., both to keratocyte cells and to View the MathML source cells, which exhibit quite different dynamics from each other. The key factors for the motile behavior inherent in each cell type are identified in our model.

*Aki Kutvonen, Takahiro Sagawa, and Tapio Ala-Nissila,
Thermodynamics of information exchange between two coupled quantum dots,
Phyical Review E 93, 032147/1-7 (2016).

[Summary] We propose a setup based on two coupled quantum dots where thermodynamics of a measurement can be quantitatively characterized. The information obtained in the measurement can be utilized by performing feedback in a manner apparently breaking the second law of thermodynamics. In this way the setup can be operated as a Maxwell's demon, where both the measurement and feedback are performed separately by controlling an external parameter. This is analogous to the case of the original Szilard engine. Since the setup contains both the microscopic demon and the engine itself, the operation of the whole measurement-feedback cycle can be explained in detail at the level of single realizations. In addition, we derive integral fluctuation relations for both the bare and coarse-grained entropy productions in the setup.

Shunpei Takeshita, Sadashige Matsuo, Takahiro Tanaka, Shu Nakaharai, Kazuhito Tsukagoshi, Takahiro Moriyama, Teruo Ono, Tomonori Arakawa, and Kensuke Kobayashi,
Anomalous behavior of 1/f noise in graphene near the charge neutrality point,
Applied Physics Letters 108, 103106/1-4 (2016).

[Summary] We investigate the noise in single layer graphene devices from equilibrium to far-from equilibrium and found that the 1/f noise shows an anomalous dependence on the source-drain bias voltage . While the Hooge’s relation is not the case around the charge neutrality point, we found that it is recovered at very low bias region. We propose that the depinning of the electron-hole puddles is induced at finite bias, which may explain this anomalous noise behavior.

*John J. Molina, Kotaro Otomura, Hayato Shiba, Hideki Kobayashi, Masaki Sano, and Ryoichi Yamamoto,
Rheological evaluation of colloidal dispersions using the smoothed profile method: formulation and applications,
Journal of Fluid Mechanics 792, 590-619 (2016).

[Summary] The smoothed profile method is extended to study the rheological behaviour of colloidal dispersions under shear flow by using the Lees–Edwards boundary conditions. We start with a reformulation of the smoothed profile method, a direct numerical simulation method for colloidal dispersions, so that it can be used with the Lees–Edwards boundary condition, under steady or oscillatory-shear flow. By this reformulation, all the resultant physical quantities, including local and total shear stresses, become available through direct calculation. Three simple rheological simulations are then performed for (1) a spherical particle, (2) a rigid bead chain and (3) a collision of two spherical particles under shear flow. Quantitative validity of these simulations is examined by comparing the viscosity with that obtained from theory and Stokesian dynamics calculations. Finally, we consider the shear-thinning behaviour of concentrated colloidal dispersions.

*Masaki Sano and Keiichi Tamai,
A Universal Transition to Turbulence in Channel Flow,
Nature Physics 12, 249-253 (2016).

[Summary] Transition from laminar to turbulent flow drastically changes the mixing, transport, and drag properties of fluids, yet when and how turbulence emerges is elusive even for simple flow within pipes and rectangular channels1,2. Unlike the onset of temporal disorder, which is identified as the universal route to chaos in confined flows3,4, characterization of the onset of spatio-temporal disorder has been an outstanding challenge because turbulent domains irregularly decay or spread as they propagate downstream. Here, through extensive experimental investigation of channel flow, we identify a distinctive transition with critical behavior. Turbulent domains continuously injected from an inlet ultimately decayed, or in contrast, spread depending on flow rates. Near a transition point, critical behavior was observed. We investigate both spatial and temporal dynamics of turbulent clusters, measuring four critical exponents, a universal scaling function and a scaling relation, all in agreement with the (2+1) dimensional directed percolation universality class.

Tomotaka Kuwahara, Takashi Mori, and Keiji Saito,
Floquet-Magnus Theory and Generic Transient Dynamics in Periodically Driven Many-Body Quantum Systems,
Annals of Physics, 96-124 (2016).

[Summary] This work explores a fundamental dynamical structure for a wide range of many-body quantum systems under periodic driving. Generically, in the thermodynamic limit, such systems are known to heat up to infinite temperature states after infinite-time evolution, irrespective of dynamical details. In the present study, instead of considering infinitely long-time scale, we aim to provide a framework to understand the long but finite time behavior, namely the transient dynamics. In the analysis, we focus on the Floquet-Magnus (FM) expansion that gives a formal expression of the effective Hamiltonian on the system. Although in general the full series expansion is not convergent in the thermodynamics limit, we give a clear relationship between the FM expansion and the transient dynamics. More precisely, we rigorously show that a truncated version of the FM expansion accurately describes the exact dynamics for a finite-time scale.

Christian Van den Broeck, Shin-ichi Sasa, Udo Seifert,
Focus on stochastic thermodynamics,
New Journal of Physics 18, 020401-020403 (2016).

[Summary] We introduce the thirty papers collected in this 'focus on' issue. The contributions explore conceptual issues within and around stochastic thermodynamics, use this framework for the theoretical modeling and experimental investigation of specific systems, and provide further perspectives on and for this active field.

*Kenji Tanabe, Ryo Matsumoto, Jun-Ichiro Ohe, Shuichi Murakami, Takahiro Moriyama, Daichi Chiba, Kensuke Kobayashi and Teruo Ono,
Observation of magnon Hall-like effect for sample-edge scattering in unsaturated YIG,
physica status solidi (b) 253, 783-787 (2016).

[Summary] We report the observation of a magnon Hall-like effect for the scattering of magnons at the sample edge in Y3Fe5O12 crystals. The experiments are performed under an out-of-plane magnetic field at room temperature using an infrared thermometry. When the magnons are incident into the sample edge in the unsaturated magnetic structure, appreciable transverse thermal gradient is detected. This thermal gradient could be attributed to magnon Hall effect for sample-edge scattering. We unexpectedly find that this effect is largely enhanced in the unsaturated regime, compared with the saturated regime where theoretical mechanism of magnon Hall effect due to the Berry curvature has been proposed previously.

Naoto Shiraishi, Takumi Matsumoto, and Takahiro Sagawa,
Measurement-feedback formalism meets information reservoirs,
New Journal of Physics 18, 013044/1-8 (2016).

[Summary] There have been two distinct formalisms of thermodynamics of information: one is the measurement-feedback formalism, which concerns bipartite systems with measurement and feedback processes, and the other is the information reservoir formalism, which considers bit sequences as a thermodynamic fuel. In this paper, we derive a second-law-like inequality by applying the measurement-feedback formalism to information reservoirs, which provides a stronger bound of extractable work than any other known inequality in the same setup. In addition, we demonstrate that the Mandal-Jarzynski model, which is a prominent model of the information reservoir formalism, is equivalent to a model obtained by the contraction of a bipartite system with autonomous measurement and feedback. Our results provide a unified view on the measurement-feedback and the information-reservoir formalisms.

*Tokuro Hata, Tomonori Arakawa, Kensaku Chida, Sadashige Matsuo, and Kensuke Kobayashi,
Giant Fano factor and bistability in a Corbino disk in the quantum Hall effect breakdown regime,
Journal of Physics: Condensed Matter 28, 055801/1-7 (2016).

[Summary] We performed noise measurements for a Corbino disk in the quantum Hall effect breakdown regime. We investigated two Corbino-disk-type devices with different sizes and observed that the Fano factor increases when the length between the contacts doubles. This observation is consistent with the avalanche picture suggested by the bootstrap electron heating model. The temperature dependence of the Fano factor indicates that the avalanche effect becomes more prominent as temperature decreases. Moreover, in the highly nonlinear regime, negative differential resistance and temporal oscillation due to bistability are found. A possible interpretation of this result is that Zener tunneling of electrons between Landau levels occurs.

#### 2015

Alexei Borodin, Ivan Corwin, Leonid Petrov, Tomohiro Sasamoto,
Spectral theory for interacting particle systems solvable by coordinate Bethe ansatz,
Communications in Mathematical Physics 339(3), 1167-1245 (2015).

[Summary] In recent studies of KPZ systems, stochastic particle systems called the q-TASEP and the q-boson zero range process have been playing important roles. In this paper we have introduced a generalized process related to the orthogonal weight of the q-Hahn polynomials. We have given a formula for the moments of the currents.

#### 2016

*Meydi Ferrier, Tomonori Arakawa, Tokuro Hata, Ryo Fujiwara, Raphaëlle Delagrange, Raphael Weil, Richard Deblock, Rui Sakano, Akira Oguri, and *Kensuke Kobayashi,
Universality of non-equilibrium fluctuations in strongly correlated quantum liquids,
Nature Physics 12, 230-235 (2015).

[Summary] Interacting quantum many-body systems constitute a fascinating research field because they form quantum liquids with remarkable properties and universal behavior. In fermionic systems, such quantum liquids are realized in helium-3 liquid, heavy fermion systems, neutron stars and cold gases. Their properties in the linear-response regime have been successfully described by the theory of Fermi liquids. The idea is that they behave as an ensemble of non-interacting‘quasi-particles’. However, non-equilibrium properties have still to be established and remain a key issue of many-body physics. Here, we show a precise experimental demonstration of Landau Fermi liquid theory extended to the non-equilibrium regime in a zero-dimensional system. Combining transport and ultra-sensitive current noise measurements, we have unambiguously identified the SU(2) and SU(4) symmetries of a quantum liquid in a carbon nanotube tuned in the universal Kondo regime. Whereas the free quasi-particle picture is found valid around equilibrium, an enhancement of the current fluctuations is detected out of equilibrium and perfectly explained by an effective charge induced by the residual interaction between quasi-particles. Moreover, an as-yet-unknown scaling law for the effective charge is discovered, suggesting a new non-equilibrium universality.

#### 2015

*Daiki Nishiguchi and Masaki Sano,
Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field,
Physical Review E 92, 052309/1-11 (2015).

[Summary] To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of nonliving self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an ac electric field. Velocity fields of the Janus particles in the crowded situation can be regarded as a sort of turbulence because it contains many vortices and their velocities change abruptly. Correlation functions of their velocity field reveal the coexistence of polar alignment and antiparallel alignment interactions, which is considered to trigger mesoscopic turbulence. Probability distributions of local order parameters for polar and nematic orders indicate the formation of local clusters with particles moving in the same direction. A broad peak in the energy spectrum of the velocity field appears at the spatial scales where the polar alignment and the cluster formation are observed. Energy is injected at the particle scale and conserved quantities such as energy could be cascading toward the larger clusters.

Masato Itami and Shin-ichi Sasa,
Derivation of Stokes’ Law from Kirkwood’s Formula and the Green-Kubo Formula via Large Deviation Theory,
Journal of Statistical Physics 161, 532-552 (2015).

[Summary] We study the friction coefficient of a macroscopic sphere in a viscous fluid at low Reynolds number. First, Kirkwood’s formula for the friction coefficient is reviewed on the basis of the Hamiltonian description of particle systems. According to this formula, the friction coefficient is expressed in terms of the stress correlation on the surface of the macroscopic sphere. Then, with the aid of large deviation theory, we relate the surface stress correlation to the stress correlation in the bulk of the fluid, where the latter is characterized by the viscosity in the Green–Kubo formula. By combining Kirkwood’s formula and the Green–Kubo formula in large deviation theory, we derive Stokes’ law without explicitly employing the hydrodynamic equations.

Harukuni Ikeda, *Kunimasa Miyazaki,
Facilitated spin model on Bethe lattice with random pinning,
EPL 112, 16001 (2015).

[Summary] We study the effects of random pinning on the Fredrickson-Andersen model on the Bethe lattice. We find that the nonergodic transition temperature rises as the fraction of the pinned spins increases and the transition line terminates at a critical point. The freezing behavior of the spins is analogous to that of a randomly pinned p-spin mean-field spin glass model which has been recently reported. The diverging behavior of correlation lengths in the vicinity of the terminal critical point is found to be identical to the prediction of the inhomogeneous mode-coupling theory at the A 3 singularity point for the glass transition.

*Shoichi Toyabe, Masaki Sano,
Nonequilibrium Fluctuations in Biological Strands, Machines, and Cells,
Journal of the Physical Society of Japan 84, 102001/1-17 (2015).

[Summary] Can physics provide a quantitative methodology and unified view to elucidate rich and diverse biological phenomena? Nonequilibrium fluctuations are key quantities. These fluctuations have universal symmetries, convey essential information about systems’ behaviors, and are experimentally accessible in most systems. We review experimental developments to extract information from the nonequilibrium fluctuations of biological systems. In particular, we focus on the three major hierarchies in small scales: strands, molecular machines, and cells.

*Sadashige Matsuo, Shunpei Takeshita, Takahiro Tanaka, Shu Nakaharai, Kazuhito Tsukagoshi, Takahiro Moriyama, Teruo Ono, Kensuke Kobayashi,
Edge mixing dynamics in graphene p–n junctions in the quantum Hall regime,
Nature Communications 6, 8066/1-6 (2015).

[Summary] Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the pn junction are realized. Additionally, these edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. Although many experimental works have addressed this issue, the microscopic dynamics of electron partition in this peculiar structure remains unclear. Here we performed shot-noise measurements on the junction in the quantum Hall regime as well as at zero magnetic field. We found that, in sharp contrast with the zero-field case, the shot noise in the quantum Hall regime is finite in the bipolar regime, but is strongly suppressed in the unipolar regime. Our observation is consistent with the theoretical prediction and gives microscopic evidence that the edge states are uniquely mixed along the pn junction.

Tomohiro Sasamoto, Herbert Spohn,
Point-interacting Brownian motions in the KPZ universality class,
Electronic Journal of Probability 20, 1-28 (2015).

[Summary] We constructed an interacting Brownian motion model in the KPZ class. In particular the model has self-duality by which we could show that the current distribution tends to the Tracy-Widom distribution. This could be used as model for colloidal particle system which shows KPZ behaviors.

Masahiko Ueda and Shin-ichi Sasa,
Replica symmetry breaking in trajectories of a driven Brownian particle,
Physical Review Letters 115, 080605/1-5 (2015).

[Summary] We study a Brownian particle passively driven by a field obeying the noisy Burgers’ equation. We demonstrate that the system exhibits replica symmetry breaking in the path ensemble with the initial position of the particle being fixed. The key step of the proof is that the path ensemble with a modified boundary condition can be exactly mapped onto the canonical ensemble of directed polymers.

Kay Brandner, Keiji Saito, and Udo Seifert ,
Thermodynamics of Micro- and Nano-Systems Driven by Periodic Temperature Variations,
Physical Review X 5, 031019 (2015).

[Summary] We introduce a general framework for analyzing the thermodynamics of small systems that are driven by both a periodic temperature variation and some external parameter modulating their energy. We show how to express total entropy production by properly identified time-independent affinities and currents without making a linear response assumption. In linear response, kinetic coefficients akin to Onsager coefficients can be identified. Specializing to a Fokker-Planck-type dynamics, we show that these coefficients can be expressed as a sum of an adiabatic contribution and one reminiscent of a Green-Kubo expression that contains deviations from adiabaticity. Furthermore, we show that the generalized kinetic coefficients fulfill an Onsager-Casimir-type symmetry tracing back to microscopic reversibility. This symmetry allows for nonidentical off-diagonal coefficients if the driving protocols are not symmetric under time reversal. We then derive a novel constraint on the kinetic coefficients that is sharper than the second law and provides an efficiency-dependent bound on power.

Misaki Ozawa, *Walter Kob, Atsushi Ikeda, Kunimasa Miyazaki,
Reply to Chakrabarty et al.: Particles move even in ideal glasses,
Proceedings of the National Academy of Sciences of the United States of America 112, E4821-E4822 (2015).

[Summary] In their letter, Chakrabarty et al. (1) point out that their data on the relaxation dynamics are inconsistent with the thermodynamic data presented in our paper (2). They argue that from their results and the predictions of the random first-order transition theory (3) one must conclude that our configurational entropy $S_c$ is “quantitatively not accurate.” In the following we will show that this conclusion is not necessarily valid.

Teruhisa S. Komatsu, Naoko Nakagawa, Shin-ichi Sasa, and Hal Tasaki,
Exact equalities and thermodynamic relations for nonequilibrium steady states,
Journal of Statistical Physics 159, 1237-1285 (2015).

[Summary] We study thermodynamic operations which bring a nonequilibrium steady state (NESS) to another NESS in physical systems under nonequilibrium conditions. We model the system by a suitable Markov jump process, and treat thermodynamic operations as protocols according to which the external agent varies parameters of the Markov process. Then we prove, among other relations, a NESS version of the Jarzynski equality and the extended Clausius relation. The latter can be a starting point of thermodynamics for NESS. We also find that the corresponding nonequilibrium entropy has a microscopic representation in terms of symmetrized Shannon entropy in systems where the microscopic description of states involves "momenta". All the results in the present paper are mathematically rigorous.

*Sadashige Matsuo, Shu Nakaharai, Katsuyoshi Komatsu, Kazuhito Tsukagoshi, Takahiro Moriyama, Teruo Ono, and Kensuke Kobayashi,
Parity effect of bipolar quantum Hall edge transport around graphene antidots,
Scientific Reports 5, 11723/1-7 (2015).

[Summary] Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene.

*Sosuke Ito, Takahiro Sagawa,
Maxwell’s demon in biochemical signal transduction with feedback loop,
Nature Communications 6, 7498 (2015).

[Summary] Signal transduction in living cells is vital to maintain life itself, where information transfer in noisy environment plays a significant role. In a rather different context, the recent intensive researches of "Maxwell's demon" - a feedback controller that utilizes information of individual molecules - has led to a unified theory of information and thermodynamics. Here we combine these two streams of researches, and show that the second law of thermodynamics with information reveals the fundamental limit of the robustness of signal transduction against environmental fluctuations. Especially, we found that the degree of robustness is quantitatively characterized by an informational quantity called transfer entropy. Our information-thermodynamic approach is applicable to biological communication inside cells, in which there is no explicit channel coding in contrast to artificial communication. Our result would open up a novel biophysical approach to understand information processing in living systems on the basis of the fundamental information-thermodynamics link.

*Timothy Halpin-Healy, Kazumasa A. Takeuchi,
A KPZ Cocktail: Shaken, not stirred… -Toasting 30 years of kinetically roughened surfaces,
Journal of Statistical Physics 160, 794-814 (2015).

[Summary] The stochastic partial differential equation proposed nearly three decades ago by Kardar, Parisi and Zhang (KPZ) continues to inspire, intrigue and confound its many admirers. Here, we i) pay debts to heroic predecessors, ii) highlight additional, experimentally relevant aspects of the recently solved 1+1 KPZ problem, iii) use an expanding substrates formalism to gain access to the 3d radial KPZ equation and, lastly, iv) examining extremal paths on disordered hierarchical lattices, set our gaze upon the fate of $d = \infty$ KPZ. Clearly, there remains ample unexplored territory within the realm of KPZ and, for the hearty, much work to be done, especially in higher dimensions, where numerical and renormalization group methods are providing a deeper understanding of this iconic equation.

Misaki Ozawa, *Walter Kob, Atsushi Ikeda, and Kunimasa Miyazaki,
Equilibrium phase diagram of a randomly pinned glass-former,
Proceedings of the National Academy of Sciences of the United States of America 112, 6914-6919 (2015).

[Summary] Confirming by experiments or simulations whether or not an ideal glass transition really exists is a daunting task, because at this point the equilibration time becomes astronomically large. Recently it has been proposed that this difficulty can be bypassed by pinning a fraction of the particles in the glass-forming system. Here we study numerically a liquid with such random pinned particles and identify the ideal glass transition point TK at which the configurational entropy vanishes, thus realizing for the first time, to our knowledge, a glass with zero entropy. We find that as the fraction of pinned particles increases, the TK line crosses the dynamical transition line, implying the existence of an end point at which theory predicts a new type of criticality.

*Taiki Haga,
Nonequilibrium Langevin equation and effective temperature for particle interacting with spatially extended environment,
Journal of Statistical Physics 159, 713-729 (2015).

[Summary] We investigate a novel type of Langevin model that describes the nonequilibrium dynamics of a classical particle interacting with a spatially extended environment. In this model, a particle, which interacts with the environment through the nonlinear interaction Hamiltonian, is driven by a constant external force, and subsequently, it reaches a nontrivial nonequilibrium steady state. We derive an effective Langevin equation for the particle in the nonequilibrium steady states. Using this equation, we calculate the effective temperature defined as the ratio of the correlation function of the velocity fluctuation to the linear response function with respect to a small perturbation. As a result, it is shown that the effective temperature associated with the time scale of the particle is identical to the kinetic temperature if the time scale of the environment and that of the particle are well separated. Furthermore, a noteworthy expression, which relates the kinetic temperature with the curvature of the driving force-mean velocity curve, is derived.

*Shin-ichi Sasa,
Collective dynamics from stochastic thermodynamics,
New Journal of Physics 17, 045024/1-14 (2015).

[Summary] From a viewpoint of stochastic thermodynamics, we derive equations that describe the collective dynamics near the order-disorder transition in the globally coupled XY model and near the synchronization-desynchronization transition in the Kuramoto model. A new way of thinking is to interpret the deterministic time evolution of a macroscopic variable as an external operation to a thermodynamic system. We then find that the irreversible work determines the equation for the collective dynamics. When analyzing the Kuramoto model, we employ a generalized concept of irreversible work which originates from a non-equilibrium identity associated with steady state thermodynamics. (IOP SELECT)

*Naoto Shiraishi, Sosuke Ito, Kyogo Kawaguchi, and Takahiro Sagawa,
Role of measurement-feedback separation in autonomous Maxwell’s demons,
New Journal of Physics 17, 045012/1-11 (2015).

[Summary] We introduce an information heat engine that is autonomous (i.e., without any time-dependent parameter) but has separated measurement and feedback processes. This model serves as a bridge between different types of information heat engines inspired by Maxwell's demon; from the original Szilard-engine type systems to the autonomous demonic setups. By analyzing our model on the basis of a general framework introduced in our previous paper (Shiraishi and Sagawa 2015 Phys. Rev. E 91 012130), we clarify the role of the separation of measurement and feedback in the integral fluctuation theorems.

*Kiyoshi Kanazawa, Tomohiko G. Sano, Takahiro Sagawa, and Hisao Hayakawa,
Minimal Model of Stochastic Athermal Systems: Origin of Non-Gaussian Noise,
Physical Review Letters 114, 090601/1-10 (2015).

[Summary] For a wide class of stochastic athermal systems, we derive Langevin-like equations driven by non-Gaussian noise, starting from master equations and developing a new asymptotic expansion. We found an explicit condition whereby the non-Gaussian properties of the athermal noise become dominant for tracer particles associated with both thermal and athermal environments. Furthermore, we derive an inverse formula to infer microscopic properties of the athermal bath from the statistics of the tracer particle. We apply our formulation to a granular motor under viscous friction and analytically obtain the angular velocity distribution function. Our theory demonstrates that the non-Gaussian Langevin equation is the minimal model of athermal systems.

*Hiroyuki Ebata and Masaki Sano,
Swimming droplets driven by a surface wave,
Scientific Reports 5, 8546/1-7 (2015).

[Summary] Self-propelling motion is ubiquitous for soft active objects such as crawling cells, ac-tive filaments, and liquid droplets moving on surfaces. Deformation and energy dissi-pation are required for self-propulsion of both living and non-living matter. From the perspective of physics, searching for universal laws of self-propelled motions in a dis-sipative environment is worthwhile, regardless of the objects’ details. In this article, we propose a simple experimental system that demonstrates spontaneous migration of a droplet under uniform mechanical agitation. As we vary control parameters, sponta-neous symmetry breaking occurs sequentially, and cascades of bifurcations of the mo-tion arise. Equations describing deformable particles and hydrodynamic simulations successfully describe all of the observed motions. This system should enable us to im-prove our understanding of spontaneous motions of self-propelled objects.

*Takaki Yamamoto, Masafumi Kuroda, and Masaki Sano,
Three-dimensional analysis of thermo-mechanically rotating cholesteric liquid crystal droplets under a temperature gradient,
EPL 109, 46001/1-6 (2015).

[Summary] We studied the rotational motion of cholesteric liquid crystal droplets under a temperaturegradient (the Lehmann effect). We found that different surface treatments, planar andhomeotropic anchoring, provided three types of droplets with different textures and geometries.The rotational velocity of these droplets depends differently on their size. Determining the threedimensionalstructures of these droplets by the fluorescence confocal polarizing microscopy, wepropose a phenomenological equation to explain the rotational behavior of these droplets. Thisresult shows that the description by the Ericksen-Leslie theory should be valid in the bulk of thedroplet, but we need to take into account the surface torque induced by temperature gradient tofully understand the Lehmann effect.

*Juan M. R. Parrondo, Jordan M. Horowitz, and Takahiro Sagawa,
Thermodynamics of information,
Nature Physics 11, 131-139 (2015).

[Summary] By its very nature, the second law of thermodynamics is probabilistic, in that its formulation requires a probabilistic description of the state of a system. This raises questions about the objectivity of the second law: does it depend, for example, on what we know about the system? For over a century, much effort has been devoted to incorporating information into thermodynamics and assessing the entropic and energetic costs of manipulating information. More recently, this historically theoretical pursuit has become relevant in practical situations where information is manipulated at small scales, such as in molecular and cell biology, artificial nano-devices or quantum computation. Here we give an introduction to a novel theoretical framework for the thermodynamics of information based on stochastic thermodynamics and fluctuation theorems, review some recent experimental results, and present an overview of the state of the art in the field.

Alexei Borodin, Ivan Corwin, Leonid Petrov, and Tomohiro Sasamoto,
Spectral theory for the q-boson particle system,
Compositio Mathematica 151, 1-67 (2015).

[Summary] We develop spectral theory for the generator of the q-Boson particle system. Our cen- tral result is a Plancherel type isomorphism theorem for this system. This theorem has various implications. It proves the completeness of the Bethe ansatz for the q-Boson generator and con- sequently enables us to solve the Kolmogorov forward and backward equations for general initial data. Owing to a Markov duality with q-TASEP, this leads to moment formulas which characterize the fixed time distribution of q-TASEP started from general initial conditions. The theorem also implies the biorthogonality of the left and right eigenfunctions.We consider limits of our q-Boson results to a discrete delta Bose gas considered previously by van Diejen, as well as to another discrete delta Bose gas that describes the evolution of moments of the semi-discrete stochastic heat equation (or equivalently, the O’Connell-Yor semi-discrete directed polymer partition function). A further limit takes us to the delta Bose gas which arises in studying moments of the stochastic heat equation / Kardar-Parisi-Zhang equation.

*Naoto Shiraishi and Takahiro Sagawa,
Fluctuation theorem for partially masked nonequilibrium dynamics,
Physical Review E 91, 012130/1-7 (2015).

[Summary] We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations.

*Tomonori Arakawa, Junichi Shiogai, Mariusz Ciorga, Martin Utz, Dieter Schuh, Makoto Kohda, Junsaku Nitta, Dominique Bougeard, Dieter Weiss, Teruo Ono, and Kensuke Kobayashi,
Shot noise induced by nonequilibrium spin accumulation,
Physical Review Letters 114, 016601/1-5 (2015).

[Summary] When an electric current passes across a potential barrier, the partition process of electrons at the barrier gives rise to the shot noise, reflecting the discrete nature of the electric charge. Here we report the observation of excess shot noise connected with a spin current which is induced by a nonequilibrium spin accumulation in an all-semiconductor lateral spin-valve device. We find that this excess shot noise is proportional to the spin current. Additionally, we determine quantitatively the spin-injection-induced electron temperature by measuring the current noise. Our experiments show that spin accumulation driven shot noise provides a novel means of investigating nonequilibrium spin transport.

Corrado Rainone, Pierfrancesco Urbani, Hajime Yoshino, *Francesco Zamponi,
Following the evolution of glassy states under external perturbations: compression and shear-strain,
Physical Review Letters 114, 015701/1-5 (2015).

[Summary] We consider the adiabatic evolution of glassy states under external perturbations. The formalism we use is very general. Here we use it for infinite-dimensional hard spheres where an exact analysis is possible. We consider perturbations of the boundary, i.e., compression or (volume preserving) shear strain, and we compute the response of glassy states to such perturbations: pressure and shear stress. We find that both quantities overshoot before the glass state becomes unstable at a spinodal point where it melts into a liquid (or yields). We also estimate the yield stress of the glass. Finally, we study the stability of the glass basins towards breaking into sub-basins, corresponding to a Gardner transition. We find that close to the dynamical transition, glasses undergo a Gardner transition after an infinitesimal perturbation.

Masato Itami and Shin-ichi Sasa,
Nonequilibrium Statistical Mechanics for Adiabatic Piston Problem,
Journal of Statistical Physics 158, 37-56 (2015).

[Summary] We consider the dynamics of a freely movable wall of mass M with one degree of freedom that separates a long tube into two regions, each of which is filled with rarefied gas particles of mass m. The gases are initially prepared at equal pressure but different temperatures, and we assume that the pressure and temperature of gas particles before colliding with the wall are kept constant over time in each region. We elucidate the energetics of the setup on the basis of the local detailed balance condition, and then derive the expression for the heat transferred from each gas to the wall. Furthermore, by using the condition, we obtain the linear response formula for the steady velocity of the wall and steady energy flux through the wall. Using perturbation expansion in a small parameter ϵ≡m/M−−−−−√, we calculate the steady velocity up to order ϵ.

#### 2014

Tomohiro Sasamoto, and Lauren Williams,
Combinatorics of the asymmetric exclusion process on a semi-infinite lattice,
Journal of Combinatorics 5(4), 419-434 (2014).

[Summary] We develop spectral theory for the generator of the q-Boson particle system. Our cen- tral result is a Plancherel type isomorphism theorem for this system. This theorem has various implications. It proves the completeness of the Bethe ansatz for the q-Boson generator and con- sequently enables us to solve the Kolmogorov forward and backward equations for general initial data. Owing to a Markov duality with q-TASEP, this leads to moment formulas which characterize the fixed time distribution of q-TASEP started from general initial conditions. The theorem also implies the biorthogonality of the left and right eigenfunctions.We consider limits of our q-Boson results to a discrete delta Bose gas considered previously by van Diejen, as well as to another discrete delta Bose gas that describes the evolution of moments of the semi-discrete stochastic heat equation (or equivalently, the O’Connell-Yor semi-discrete directed polymer partition function). A further limit takes us to the delta Bose gas which arises in studying moments of the stochastic heat equation / Kardar-Parisi-Zhang equation.

Ismael S. S. Carrasco, Kazumasa A. Takeuchi, Silvio da Costa Ferreira Junior, and *Tiago José Oliveira,
Interface fluctuations for deposition on enlarging flat substrates,
New Journal of Physics 16, 123057/1-20 (2014).

[Summary] We investigate solid-on-solid models that belong to the Kardar-Parisi-Zhang (KPZ) universality class on substrates that expand laterally at a constant rate. Despite the null global curvature, we show that all investigated models have asymptotic height distributions and spatial covariances in agreement with those expected for the KPZ subclass for curved surfaces. In 1+1 dimensions, the height distribution and covariance are given by the GUE Tracy-Widom distribution and the Airy2 process instead of the GOE and Airy1 foreseen for flat interfaces. These results imply that when the KPZ class splits into curved and flat subclasses, as conventionally considered, the expanding substrate may play a role equivalent to, or perhaps more important than, the global curvature. Moreover, the translational invariance of the interfaces evolving on growing domains allowed us to accurately determine, in 2+1 dimensions, the analog of the GUE Tracy-Widom distribution for height distribution and that of the Airy2 process for spatial covariance. Temporal covariance is also calculated and shown to be universal in each dimension and in each of the two subclasses. A logarithmic correction associated with the duplication of columns is observed and theoretically elucidated. Finally, crossover between regimes with fixed-size and enlarging substrates is also investigated.

Saroj Kumar Nandi, *Giulio Biroli, Jean-Philippe Bouchaud, Kunimasa Miyazaki, and David R. Reichman,
Critical dynamical heterogeneities close to continuous second-order glass transitions,
Physical Review Letters 113, 245701/1-5 (2014).

[Summary] We analyze, using inhomogeneous mode-coupling theory, the critical scaling behavior of the dynamical susceptibility at a distance ε from continuous second-order glass transitions. We find that the dynamical correlation length ξ behaves generically as ε−1/3 and that the upper critical dimension is equal to six. More surprisingly, we find that ξ grows with time as ln2t exactly at criticality. All of these results suggest a deep analogy between the glassy behavior of attractive colloids or randomly pinned supercooled liquids and that of the random field Ising model.

Alexei Borodin, *Ivan Corwin, Tomohiro Sasamoto,
From duality to determinants for q-TASEP and ASEP,
Annals of Probability 42, 2314-2382 (2014).

[Summary] We prove duality relations for two interacting particle systems: the q-deformed totally asymmetric simple exclusion process (q-TASEP) and the asymmetric simple exclusion process (ASEP). Expectations of the duality functionals correspond to certain joint moments of particle locations or integrated currents, respectively. Duality implies that they solve systems of ODEs. These systems are integrable and for particular step and half- stationary initial data we use a nested contour integral ansatz to provide ex- plicit formulas for the systems’ solutions, and hence also the moments.

Takahiro Nemoto, Vivien Lecomte, Shin-ichi Sasa, and *Friédéric van Wijland,
Finite size effects in a mean-field kinetically constrained model: dynamical glassiness and quantum criticality,
Journal of Statistical Mechanics -, P10001/1-38 (2014).

[Summary] On the example of a mean-field Fredrickson-Andersen kinetically constrained model, we focus on the known property that equilibrium dynamics take place at a first-order dynamical phase transition point in the space of time-realizations. We investigate the finite-size properties of this first order transition. By discussing and exploiting a mapping of the classical dynamical transition -an argued glassiness signature- to a first-order quantum transition, we show that the quantum analogy can be exploited to extract finite-size properties, which in many respects are similar to those in genuine mean-field quantum systems with a first-order transition. We fully characterize the finite-size properties of the order parameter across the first order transition.

Hajime Yoshino and Francesco Zamponi,
The shear modulus of glasses: results from the full replica symmetry breaking solution,
Physical Review E 90, 022302/1-14 (2014).

[Summary] We compute the shear modulus of amorphous hard and soft spheres, using the exact solution in infinite spatial dimensions that has been developed recently. We characterize the behavior of this observable in the whole phase diagram, and in particular around the glass and jamming transitions. Our results are consistent with other theoretical approaches, which are unified within this general picture, and they are also consistent with numerical and experimental results. Furthermore, we discuss some properties of the out-of-equilibrium dynamics after a deep quench close to the jamming transition, and we show that a combined measure of the shear modulus and of the mean square displacement allows one to probe experimentally the complex structure of phase space predicted by the full replica-symmetry-breaking solution.

*Naoko Nakagawa,
Physical Review E 90, 022108/1-6 (2014).

[Summary] We develop a unified treatment of pumping and nonequilibrium thermodynamics. We show that the pumping current generated through an adiabatic mechanical operation in equilibrium can be expressed in terms of the stationary distribution of the corresponding driven nonequilibrium system. We also show that the total transfer in pumping can be evaluated from the work imported to the driven counterpart. These findings lead us to a unified viewpoint for pumping and nonequilibrium thermodynamics.

*Takahiro Tanaka, Tomonori Arakawa, Masahiro Maeda, Kensuke Kobayashi, Yoshitaka Nishihara, Teruo Ono, Takayuki Nozaki, Akio Fukushima, and Shinji Yuasa,
Leak current estimated from the shot noise in magnetic tunneling junctions,
Applied Physics Letters 105, 042405/1-4 (2014).

[Summary] We performed the shot noise measurement in epitaxial Fe/MgO/Fe-based magnetic tunneling junctions (MTJs) with various MgO thicknesses between 1.1 nm and 1.625nm. While the Fano factor to characterize the shot noise is very close to 1 in MTJs with MgO barrier thicker than 1.2nm, the magnetic configuration-dependent reduction of the Fano factor for MTJs with thin MgO barrier was observed, which is mainly due to the existence of leakage current. By using a simple parallel circuit model, we demonstrated that the contribution of the leak current can be sensitively derived from the shot noise.

Suman G. Das, Abhishek Dhar, Keiji Saito, Christian B. Mendl, Herbert Spohn,
Numerical test of hydrodynamic fluctuation theory in the Fermi-Pasta-Ulam chain,
Physical Review E 90, 12124/1-11 (2014).

[Summary] Recent work has developed a nonlinear hydrodynamic fluctuation theory for a chain of coupled anharmonic oscillators governing the conserved fields, namely stretch, momentum, and energy. The linear theory yields two propagating sound modes and one diffusing heat mode. In contrast, the nonlinear theory predicts that, at long times, the sound mode correlations satisfy Kardar-Parisi-Zhang (KPZ) scaling, while the heat mode correlations satisfies Levy-walk scaling. In the present contribution we report on molecular dynamics simulations of Fermi-Pasta-Ulam chains to compute various spatiotemporal correlation functions and compare them with the predictions of the theory. We find very good agreement in many cases, but also some deviations.

*Kiyoshi Kanazawa, Takahiro Sagawa, and Hisao Hayakawa,
Energy pumping in electrical circuits under avalanche noise,
Physical Review E 90, 012115/1-8 (2014).

[Summary] We theoretically study energy pumping processes in an electrical circuit with avalanche diodes, where non-Gaussian athermal noise plays a crucial role. We show that a positive amount of energy (work) can be extracted by an external manipulation of the circuit in a cyclic way, even when the system is spatially symmetric. We discuss the properties of the energy pumping process for both quasistatic and finite-time cases, and analytically obtain formulas for the amounts of the work and the power. Our results demonstrate the significance of the non-Gaussianity in energetics of electrical circuits.

*Jordan M. Horowitz and Takahiro Sagawa,
Equivalent Definitions of the Quantum Nonadiabatic Entropy Production,
Journal of Statistical Physics 156, 55-65 (2014).

[Summary] The nonadiabatic entropy production is a useful tool for the thermodynamic analysis of continuously dissipating, nonequilibrium steady states. For open quantum systems, two seemingly distinct definitions for the nonadiabatic entropy production have appeared in the literature, one based on the quantum relative entropy and the other based on quantum trajectories. We show that these two formulations are equivalent. Furthermore, this equivalence leads us to a proof of the monotonicity of the quantum relative entropy under a special class of completely-positive, trace-preserving quantum maps, which circumvents difficulties associated with the noncommuntative structure of operators.

*Kensaku Chida, Tokuro Hata, Tomonori Arakawa, Sadashige Matsuo, Yoshitaka Nishihara, Takahiro Tanaka, Teruo Ono, and Kensuke Kobayashi,
Avalanche electron bunching in a Corbino disk in the quantum Hall effect breakdown regime,
Physical Review B 89, 235318/1-4 (2014).

[Summary] We have measured the current noise in a device with Corbino geometry to investigate the dynamics of electrons in the breakdown regime of the integer quantum Hall effect (QHE). In the breakdown regime, the Fano factor of the current noise exceeds 103, which indicates the presence of electron bunching. As super-Poissonian current noise is observed only in the breakdown regime, the bunching effect is related to the QHE breakdown. These observations support a QHE breakdown mechanism that involves an electron avalanche.

*Jonne V. Koski, Ville F. Maisi, Takahiro Sagawa, and Jukka P. Pekola,
Experimental Observation of the Role of Mutual Information in the Nonequilibrium Dynamics of a Maxwell Demon,
Physical Review Letters 113, 030601/1-5 (2014).

[Summary] We validate experimentally a fluctuation relation known as generalized Jarzynski equality governing the work distribution in a feedback-controlled system. The feedback control is performed on a single electron box analogously to the original Szilard engine. In the generalized Jarzynski equality, mutual information is treated on an equal footing with the thermodynamic work. Our measurements provide the first evidence of the role of mutual information in the fluctuation theorem and thermodynamics of irreversible processes.

*Kyogo Kawaguchi, Shin-ichi Sasa, and Takahiro Sagawa,
Nonequilibrium dissipation-free transport in F1-ATPase and the thermodynamic role of asymmetric allosterism,
Biophysical Journal 106, 2450-2457 (2014).

[Summary] F1-ATPase (or F1), the highly-efficient and reversible biochemical engine, has motivated physicists as well as biologists to imagine the design principles governing machines in the fluctuating world. Recent experiments have clarified yet another interesting property of F1; the dissipative heat inside the motor is very small, irrespective of the velocity of rotation and energy transport. Conceptual interest is devoted to the fact that the amount of internal dissipation is not simply determined by the sequence of equilibrium pictures, but also relies on the rotational-angular dependence of nucleotide affinity, which is a truly nonequilibrium aspect. We propose that the totally asymmetric allosteric model (TASAM), where adenosine triphosphate (ATP) binding to F1 is assumed to have low dependence on the angle of the rotating shaft, produces results that are most consistent with the experiment. Theoretical analysis proves the crucial role of two time scales in the model, which explains the universal mechanism to produce the internal dissipation-free feature. The model reproduces the characteristic torque dependence of the rotational velocity of F1, and predicts that the internal dissipation upon the ATP synthesis direction rotation becomes large at the low nucleotide condition.

*Kyogo Kawaguchi, Shin-ichi Sasa, and Takahiro Sagawa,
Nonequilibrium Dissipation-free Transport in F1-ATPase and the Thermodynamic Role of Asymmetric Allosterism,
Biophysical Journal 106, 2450–2457 (2014).

[Summary] F1-ATPase (or F1), the highly efficient and reversible biochemical engine, has motivated physicists as well as biologists to imagine the design principles governing machines in the fluctuating world. Recent experiments have clarified yet another interesting property of F1; the dissipative heat inside the motor is very small, irrespective of the velocity of rotation and energy transport. Conceptual interest is devoted to the fact that the amount of internal dissipation is not simply determined by the sequence of equilibrium pictures, but also relies on the rotational-angular dependence of nucleotide affinity, which is a truly nonequilibrium aspect. We propose that the totally asymmetric allosteric model (TASAM), where adenosine triphosphate (ATP) binding to F1 is assumed to have low dependence on the angle of the rotating shaft, produces results that are most consistent with the experiments. Theoretical analysis proves the crucial role of two time scales in the model, which explains the universal mechanism to produce the internal dissipation-free feature. The model reproduces the characteristic torque dependence of the rotational velocity of F1 and predicts that the internal dissipation upon the ATP synthesis direction rotation becomes large at the low nucleotide condition.

*Hiroki Ohta and Shin-ichi Sasa,
Jamming transition in kinetically constrained models with the parity symmetry,
Journal of Statistical Physics 155, 827-842 (2014).

[Summary] A class of kinetically constrained models with reflection symmetry is proposed as an extension ofthe Fredrickson-Andersen model. It is proved that the proposed model on the square lattice exhibits a freezingtransition at a non-trivial density. It is conjectured by numerical experiments that the known mechanism of thesingular behaviors near the freezing transition in a previously studied model (spiral model) is not responsiblefor that in the proposed model.

Masato Itami and Shin-ichi Sasa,
Macroscopically measurable force induced by temperature discontinuities at solid-gas interfaces,
Physical Review E 89, 052106/1-6 (2014).

[Summary] We consider a freely movable solid that separates a long tube into two regions, each of which isfilled with a dilute gas. The gases in each region are initially prepared at the same pressure butdifferent temperatures. Under the assumption that the pressure and temperatures of gas particlesbefore colliding with the solid are kept constant over time, we show that temperature gaps appearingon the solid surface generate a force. We provide a quantitative estimation of the force, which turnsout to be large enough to be observed by a macroscopic measurement.

*Kenji Tanabe, Ryo Matsumoto, Jun-ichiro Ohe, Shuichi Murakami, Takahiro Moriyama, Daichi Chiba, Kensuke Kobayashi, and Teruo Ono,
Real-time observation of Snell’s law for spin waves in a thin ferromagnetic film,
Applied Physics Express 7, 053001/1-4 (2014).

[Summary] We report the real-time observation of spin-wave propagation across a step inserted between two ferromagnetic films with different thicknesses. Because the dispersion relation of the spin wave depends on the thickness of the film, the step works as a junction to affect the spin wave propagation. When the spin wave transmits through the junction, the wavenumber undergoes modulation as per Snell’s law, which states that the refraction index is proportional to the wavenumber. From the viewpoint of magnonics, the present achievement opens up new possibilities of controlling the wavenumber of spin waves.

Julian Stark, Kay Brandner, Keiji Saito, and Udo Seifert,
A Classical Nernst Engine,
Physical Review Letters 112, 140601/1-5 (2014).

[Summary] We introduce a simple model for an engine based on the Nernst effect. In the presence of a magnetic field, a vertical heat current can drive a horizontal particle current against a chemical potential. For a microscopic model invoking classical particle trajectories subject to the Lorentz force, we prove a universal bound 0.172 for the ratio between the maximum efficiency and the Carnot efficiency. This bound, as the slightly lower one 1/6 for efficiency at maximum power, can indeed be saturated for a large magnetic field and small fugacity.

*Takahiro Sagawa,
Thermodynamic and Logical Reversibilities Revisited,
Journal of Statistical Mechanics, 1-33 (2014).

[Summary] We review and investigate the general theory of the thermodynamics of computation, and derive the fundamental inequalities that set the lower bounds of the work requirement and the heat emission during a computation. These inequalities constitute the generalized Landauer principle, where the information contents are involved in the second law of thermodynamics. We discuss in detail the relationship between the thermodynamic and logical reversibilities; the former is related to the entropy production in the total system including a heat bath, while the latter is related to the entropy change only in the logical states of the memory. In particular, we clarify that any logically irreversible computation can be performed in a thermodynamically reversible manner in the quasi-static limit, which does not contradict the conventional Landauer principle. Our arguments would serve as the theoretical foundation of the thermodynamics of computation in terms of modern statistical physics.

*Shin-ichi Sasa,
Derivation of hydrodynamics from the Hamiltonian description of particle systems,
Physical Review Letters 112, 100602 (2014).

[Summary] Hamiltonian particle systems may exhibit non-linear hydrodynamic phenomena as the time evolution of the density fields of energy, momentum, and mass.　In this Letter, an exact equation describing the time evolution is derived assuming the local Gibbs distribution at initial time. The key concept in the derivation is an identity similar to the fluctuation theorems. The Navier-Stokes equation is obtained as a result of simple perturbation expansions in a small parameter that represents the scale separation.

*Takahiro Nemoto, and Shin-ichi Sasa,
Computation of large deviation statistics via iterative measurement-and-feedback procedure,
Physical Review Letters 112, 090602/1-5 (2014).

[Summary] We propose a computational method for large deviation statistics　of time-averaged quantities in general Markov processes. In our proposed method, we repeat a response measurement　against external forces, where the forces are determined by the previous measurement as a feedback.　Consequently, we obtain a set of stationary states corresponding to an exponential family　of distributions, each of which shows rare events in the original system as the typical behavior. As a demonstration of our method,　we study large deviation statistics of one-dimensional lattice gas models.

*Masahito Ueda and Shin-ichi Sasa,
Calculation of 1RSB transition temperature of spin glass models on regular random graphs under the replica symmetric ansatz,
Journal of Statistical Mechanics: Theory and Experiment P02005/1-21 (2014).

[Summary] We study p-spin glass models on regular random graphs.By analyzing the Franz-Parisi potential with a two-body cavity field approximation under the replica symmetric ansatz, we obtain a good approximation of the 1RSB transition temperature for $p=3$.　Our calculation method is much easier than the 1RSB cavity method because the result is obtained by solving self-consistent equations with Newton's method.

*Shin-ichi Sasa,
Possible extended forms of thermodynamic entropy,
Journal of Statistical Mechanics: Theory and Experiment , P01004/1-16 (2014).

[Summary] Thermodynamic entropy is determined by a heat measurement through the Clausius equality. The entropy then formalizesa fundamental limitation of operations by the second lawof thermodynamics. The entropy is also expressed as the Shannon entropy of the microscopic degrees of freedom. Whenever an extension of thermodynamic entropy is attempted,we must pay special attention to how its three different aspects just mentioned are altered. In this paper, we discuss possible extensions of the thermodynamic entropy.

*Kazumasa A. Takeuchi,
Experimental approaches to universal out-of-equilibrium scaling laws: turbulent liquid crystal and other developments,
Journal of Statistical Mechanics: Theory and Experiment P01006/1-28 (2014).

[Summary] This is a brief survey of recent experimental studies on out-of-equilibrium scaling laws, focusing on two prominent situations where nontrivial universality classes have been identified theoretically: absorbing-state phase transitions and growing interfaces. First the paper summarizes the main results obtained for electrically driven turbulent liquid crystals, which exhibited the scaling laws for the directed percolation class at the transition between two turbulent regimes, and those for the Kardar-Parisi-Zhang class in the supercritical phase where one turbulent regime invades the other. Other experimental investigations on these universality classes and related situations are then overviewed and discussed. Some remarks on analyses of these scaling laws are also given from the practical viewpoint.

Takeshi Kuroiwa and *Kunimasa Miyazaki,
Brownian motion with multiplicative noises revisited,
Journal of Physics A: Mathematical and Theoretical 47, 012001/1-8 (2014).

[Summary] The Langevin equation with multiplicative noise and a state-dependent transport coefficient should always complemented with the proper interpretation rule of the noise, such as the Itˆo and Stratonovich conventions. Although the mathematical relationship between the different rules and how to translate from one rule to another are well established, the subject of which is amore physically natural rule still remains controversial. In this communication, we derive the overdamped Langevin equation with multiplicative noise for Brownian particles, by systematically eliminating the fast degrees of freedomof the underdamped Langevin equation. The Langevin equations obtained here vary depending on the choice of the noise conventions but they are different representations for an identical phenomenon. The results apply to multivariable, nonequilibrium, non-stationary systems, and other general settings.

Johannes-Geert Hagmann, Naoko Nakagawa, and *Michel Peyrard,
Characterization of the low-temperature properties of a simplified protein model,
Physical Review E 89, 012705/1-13 (2014).

[Summary] Prompted by results that showed that a simple protein model, the frustrated Go ̄ model, appears to exhibit a transition reminiscent of the protein dynamical transition, we examine the validity of this model to describe the low-temperature properties of proteins. First, we examine equilibrium fluctuations. We calculate its incoherent neutron-scattering structure factor and show that it can be well described by a theory using the one-phonon approximation. By performing an inherent structure analysis, we assess the transitions among energy states at low temperatures. Then, we examine nonequilibrium fluctuations after a sudden cooling of the protein. We investigate the violation of the fluctuation-dissipation theorem in order to analyze the protein glass transition. We find that the effective temperature of the quenched protein deviates from the temperature of the thermostat, however it relaxes towards the actual temperature with an Arrhenius behavior as the waiting time increases. These results of the equilibrium and nonequilibrium studies converge to the conclusion that the apparent dynamical transition of this coarse-grained model cannot be attributed to a glassy behavior.

*Hirokazu Tanimoto and Masaki Sano,
A simple force-motion relation for migrating cells revealed by multipole analysis of traction stress,
Biophysical Journal 106, 16-25 (2014).

[Summary] For biophysical understanding of cell motility, the relationship between mechanical force and cell migration must be uncovered, but it remains elusive. Since cells migrate at small scale in dissipative circumstances, the inertia force is negligible and all forces should cancel out. This implies that one must quantify the spatial pattern of the force instead of just the summation to elucidate the force-motion relation. Here, we introduced multipole analysis to quantify the traction stress dynamics of migrating cells. We measured the traction stress of Dictyostelium discoideum cells and investigated the lowest two moments, the force dipole and quadrupole moments, which reflect rotational and front-rear asymmetries of the stress field. We derived a simple force-motion relation in which cells migrate along the force dipole axis with a direction determined by the force quadrupole. Furthermore, as a complementary approach, we also investigated fine structures in the stress field that show front-rear asymmetric kinetics consistent with the multipole analysis. The tight force-motion relation enables us to predict cell migration only from the traction stress patterns.

#### 2013

*Takahiro Sagawa and Masahito Ueda,
Role of mutual information in entropy production under information exchanges,
New Journal of Physics 15, 125012/1-23 (2013).

[Summary] We relate the information exchange between two stochastic systems to the nonequilibrium entropy production in the whole system. By deriving a general formula that decomposes the total entropy production into the thermodynamic and informational parts, we obtain nonequilibrium equalities such as the fluctuation theorem in the presence of information processing. Our results apply not only to situations under measurement and feedback control but also to those under multiple information exchanges between two systems, giving the fundamental energy cost for information processing and elucidating the thermodynamic and informational roles of a memory in information processing. We point out a dual relationship between measurement and feedback.

*Jung Jun Park, Kang-Hwan Kim, Takahiro Sagawa, and Sang Wook Kim,
Heat Engine Driven by Purely Quantum Information,
Physical Review Letters 111, 230402/1-5 (2013).

[Summary] The key question of this Letter is whether work can be extracted from a heat engine by using purely quantum mechanical information. If the answer is yes, what is its mathematical formula? First, by using a bipartite memory we show that the work extractable from a heat engine is bounded not only by the free energy change and the sum of the entropy change of an individual memory but also by the change of quantum mutual information contained inside the memory. We then find that the engine can be driven by purely quantum information, expressed as the so-called quantum discord, forming a part of the quantum mutual information. To confirm it, as a physical example we present the Szilard engine containing a diatomic molecule with a semipermeable wall.

*Keiji Saito and Takeo Kato,
Kondo signature in heat transfer via a local two-state system,
Physical Review Letters 111, 214301/1-4 (2013).

[Summary] We study the Kondo effect in heat transport via a local two-state system. This system is described by the spin-boson Hamiltonian with Ohmic dissipation, which can be mapped onto the Kondo model with anisotropic exchange coupling. We calculate thermal conductance by the Monte Carlo method based on the exact formula. Thermal conductance has a scaling form κ=(k2BTK/)f(α,T/TK), where TK and α indicate the Kondo temperature and dimensionless coupling strength, respectively. Temperature dependence of conductance is classified by the Kondo temperature as κ(T/TK)3 for TTK and κ(kBT/ωc)2α1 for TTK. Similarities to the Kondo signature in electric transport are discussed.

*Hiroyuki Ebata and Masaki Sano,
Bifurcation from stable holes to replicating holes in vibrated dense suspensions,
Physical Review E 88, 053007/1-8 (2013).

[Summary] In vertically vibrated starch suspensions, we observe bifurcations from stable holes to replicating holes. Abovea certain acceleration, ﬁnite-amplitude deformations of the vibrated surface continue to grow until void penetratesﬂuid layers, and a hole forms. We studied experimentally and theoretically the parameter dependence of the holesand their stabilities. In suspensions of small dispersed particles, the circular shapes of the holes are stable. However,we ﬁnd that larger particles or lower surface tension of water destabilize the circular shapes; this indicates theimportance of capillary forces acting on the dispersed particles. Around the critical acceleration for bifurcation,holes show intermittent large deformations as a precursor to hole replication. We applied a phenomenologicalmodel for deformable domains, which is used in reaction-diffusion systems. The model can explain the basicdynamics of the holes, such as intermittent behavior, probability distribution functions of deformation, and timeintervals of replication. Results from the phenomenological model match the linear growth rate below criticalitythat was estimated from experimental data.

*Patrik L. Ferrari, Tomohiro Sasamoto, Herbert Spohn,
Coupled Kardar-Parisi-Zhang Equations in One Dimension,
Journal of Statistical Physics 153, 377-399 (2013).

[Summary] Over the past years our understanding of the scaling properties of the solutions to the one-dimensional KPZ equation has advanced considerably, both theoretically and experimentally. In our contribution we export these insights to the case of coupled KPZ equations in one dimension. We establish equivalence with nonlinear fluctuating hydrodynamics for multi-component driven stochastic lattice gases. To check the predictions of the theory, we perform Monte Carlo simulations of the two-component AHR model. Its steady state is computed using the matrix product ansatz. Thereby all coefficients appearing in the coupled KPZ equations are deduced from the microscopic model. Time correlations in the steady state are simulated and we confirm not only the scaling exponent, but also the scaling function and the non-universal coefficients.

*Tatsuro Yuge, Takahiro Sagawa, Ayumu Sugita, and Hisao Hayakawa,
Geometrical Excess Entropy Production in Nonequilibrium Quantum Systems,
Journal of Statistical Physics 153, 412-441 (2013).

[Summary] For open systems described by the quantum Markovian master equation, we study a possible extension of the Clausius equality to quasistatic operations between nonequilibrium steady states (NESSs). We investigate the excess heat divided by temperature (i.e., excess entropy production) which is transferred into the system during the operations. We derive a geometrical expression for the excess entropy production, which is analogous to the Berry phase in unitary evolution. Our result implies that in general one cannot define a scalar potential whose difference coincides with the excess entropy production in a thermodynamic process, and that a vector potential plays a crucial role in the thermodynamics for NESSs. In the weakly nonequilibrium regime, we show that the geometrical expression reduces to the extended Clausius equality derived by Saito and Tasaki (J. Stat. Phys. 145:1275, 2011). As an example, we investigate a spinless electron system in quantum dots. We find that one can define a scalar potential when the parameters of only one of the reservoirs are modified in a non-interacting system, but this is no longer the case for an interacting system.

Sosuke Ito and Takahiro Sagawa,
Information Thermodynamics on Causal Networks,
Physical Review Letters 111, 180603/1-6 (2013).

[Summary] We study nonequilibrium thermodynamics of complex information flows induced by interactions between multiple fluctuating systems. Characterizing nonequilibrium dynamics by causal networks (i.e., Bayesian networks), we obtain novel generalizations of the second law of thermodynamics and the fluctuation theorem, which include an informational quantity characterized by the topology of the causal network. Our result implies that the entropy production in a single system in the presence of multiple other systems is bounded by the information flow between these systems. We demonstrate our general result by a simple model of biochemical adaptation.

*Sang Wook Kim, Kang-Hwan Kim, Takahiro Sagawa, Simone De Liberato, and Masahito Ueda,
Physical Review Letters 111, 188902/1 (2013).

[Summary] A Reply to the Comment by M. Plesch et al.

*Sadashige Matsuo, Kensaku Chida, Daichi Chiba, Teruo Ono, Keith Slevin, Kensuke Kobayashi, Tomi Ohtsuki, Cui-Zu Chang, Ke He, Xu-Cun Ma, and Qi-Kun Xue,
Experimental Proof of Universal Conductance Fluctuation in Quasi-1D Epitaxial Bi2Se3 Wires,
Physical Review B 88, 155438/1-8 (2013).

[Summary] We report on conductance fluctuation in quasi-one-dimensional wires made of epitaxial Bi2Se3 thin film. We found that this type of fluctuation decreases as the wire length becomes longer and that the amplitude of the fluctuation is well scaled to the coherence, thermal diffusion, and wire lengths, as predicted by conventional universal conductance fluctuation (UCF) theory. Additionally, the amplitude of the fluctuation can be understood to be equivalent to the UCF amplitude of a system with strong spin-orbit interaction and no time-reversal symmetry. These results indicate that the conductance fluctuation in Bi2Se3 wires is explainable through UCF theory. This work verifies the scaling relationship of UCF in a system with strong spin-orbit interaction.

*Tomonori Arakawa, Yoshitaka Nishihara, Masahiro Maeda, Shota Norimoto, and Kensuke Kobayashi,
Cryogenic amplifier for shot noise measurement at 20 mK,
Applied Physics Letters 103, 172104/1-4 (2013).

[Summary] We developed a shot noise measurement system for mesoscopic conductors (typical resistance h/2e^2) at very low temperature (20 mK). To realize required high-resolution measurement, we made a high-electron-mobility-transistor (HEMT)-based cryogenic amplifier working at a target frequency range (@2.5 MHz), whose gain flatness and input voltage noise were carefully tuned. We can suppress the 1/f noise of the amplifier by using two HEMTs in parallel. The performance of the noise measurement system at 20mK was demonstrated for a quantum point contact with high experimental accuracy below 10^-29 A^2/Hz.

Takashi Imamura, *Tomohiro Sasamoto, Herbert Spohn,
On the equal time two-point distribution of the one-dimensional KPZ equation by replica,
Journal of Physics A: Mathematical and Theoretical 46, 355002/1-9 (2013).

[Summary] In a recent contribution, Dotsenko establishes a Fredholm determinant formula for the two-point distribution of the Kardar–Parisi–Zhang equation in the long time limit and starting from narrow wedge initial conditions. We establish that his expression is identical to the Fredholm determinant resulting from the Airy2 process.

*Jonne V. Koski, Takahiro Sagawa, O-P. Saira, Y. Yoon, A. Kutvonen, P. Solinas, M. Möttönen, T. Ala-Nissila, and Jukka P. Pekola,
Distribution of entropy production in a single-electron box,
Nature Physics 9, 644-648 (2013).

[Summary] Recently, the fundamental laws of thermodynamics have been reconsidered for small systems. The discovery of the fluctuation relations has spurred theoretical and experimental studies. The concept of entropy production has been extended to the microscopic level by considering stochastic trajectories of a system coupled to a heat bath. However, this has not been studied experimentally if there are multiple thermal baths present. Here, we measure, with high precision, the distributions of microscopic entropy production in a single-electron box consisting of two islands with a tunnel junction. The islands are coupled to separate heat baths at different temperatures, maintaining a steady thermal non-equilibrium. We demonstrate that stochastic entropy production from trajectories of electronic transitions is related to thermodynamic entropy production from dissipated heat in the respective thermal baths. We verify experimentally that the fluctuation relations for both definitions are satisfied. Our results reveal the subtlety of irreversible entropy production in non-equilibrium.

*Kang Kim, Shinji Saito, Kunimasa Miyazaki, Giulio Biroli, and *David R. Reichman,
Dynamic Length Scales in Glass-Forming Liquids: An Inhomogeneous Molecular Dynamics Simulation Approach,
The Journal of Physical Chemistry B 117, 13259–13267 (2013).

[Summary] In this work, we numerically investigate a new method for the characterization of growing length scales associated with spatially heterogeneous dynamics of glass-forming liquids. This approach, motivated by the formulation of the inhomogeneous mode-coupling theory (IMCT) [Biroli, G.; et al. Phys. Rev. Lett. 2006 97, 195701], utilizes inhomogeneous molecular dynamics simulations in which the system is perturbed by a spatially modulated external potential. We show that the response of the two-point correlation function to the external field allows one to probe dynamic correlations. We examine the critical properties shown by this function, in particular, the associated dynamic correlation length, that is found to be comparable to the one extracted from standardly employed four-point correlation functions. Our numerical results are in qualitative agreement with IMCT predictions but suggest that one has to take into account fluctuations not included in this mean-field approach to reach quantitative agreement. Advantages of our approach over the more conventional one based on four-point correlation functions are discussed.

*Jordan M. Horowitz, Takahiro Sagawa, and Juan M. R. Parrondo,
Imitating Chemical Motors with Optimal Information Motors,
Physical Review Letters 111, 010602/1-5 (2013).

[Summary] To induce transport, detailed balance must be broken. A common mechanism is to bias the dynamics with a thermodynamic fuel, such as chemical energy. An intriguing, alternative strategy is for a Maxwell demon to effect the bias using feedback. We demonstrate that these two different mechanisms lead to distinct thermodynamics by contrasting a chemical motor and information motor with identical dynamics. To clarify this difference, we study both models within one unified framework, highlighting the role of the interaction between the demon and the motor. This analysis elucidates the manner in which information is incorporated into a physical system.

*Kiyoshi Kanazawa, Takahiro Sagawa, and Hisao Hayakawa,
Heat conduction induced by non-Gaussian athermal fluctuations,
Physical Review E 87, 052124/1-10 (2013).

[Summary] We study the properties of heat conduction induced by non-Gaussian noises from athermal environments. We find that new terms should be added to the conventional Fourier law and the fluctuation theorem for the heat current, where its average and fluctuation are determined not only by the noise intensities but also by the non-Gaussian nature of the noises. Our results explicitly show the absence of the zeroth law of thermodynamics in athermal systems.