A02 TAKASU, Yosuke |Proposed Research Projects (2016-2017)

Paper | Original Paper


Takafumi Tomita, Shuta Nakajima, Ippei Danshita, Yosuke Takasu and Yoshiro Takahashi,
Observation of the Mott insulator to superfluid crossover of a driven-dissipative Bose-Hubbard system,
Science Advances 3, e1701513 (2017).

[Summary] Dissipation is ubiquitous in nature and plays a crucial role in quantum systems such as causing decoherence of quantum states. Recently, much attention has been paid to an intriguing possibility of dissipation as an efficient tool for the preparation and manipulation of quantum states. We report the realization of successful demonstration of a novel role of dissipation in a quantum phase transition using cold atoms. We realize an engineered dissipative Bose-Hubbard system by introducing a controllable strength of two-body inelastic collision via photoassociation for ultracold bosons in a three-dimensional optical lattice. In the dynamics subjected to a slow ramp-down of the optical lattice, we find that strong on-site dissipation favors the Mott insulating state: The melting of the Mott insulator is delayed, and the growth of the phase coherence is suppressed. The controllability of the dissipation is highlighted by quenching the dissipation, providing a novel method for investigating a quantum many-body state and its nonequilibrium dynamics.

Mateusz Borkowski, Alexei A. Buchachenko, Roman Ciuryło, Paul S. Julienne, Hirotaka Yamada, Yuu Kikuchi, Kakeru Takahashi, Yosuke Takasu, and Yoshiro Takahashi,
Beyond-Born-Oppenheimer effects in sub-kHz-precision photoassociation spectroscopy of ytterbium atoms,
Physical Review A 96, 063405 (2017).

[Summary] We present high-resolution two-color photoassociation spectroscopy of Bose-Einstein condensates of ytterbium atoms. The use of narrow Raman resonances and careful examination of systematic shifts enabled us to measure 13 bound-state energies for three isotopologues of the ground-state ytterbium molecule with standard uncertainties of the order of 500 Hz. The atomic interactions are modeled using an ab initio based mass-scaled Born-Oppenheimer potential whose long-range van der Waals parameters and total WKB phase are fitted to experimental data. We find that the quality of the fit of this model, of about 112.9 kHz (rms) can be significantly improved by adding the recently calculated beyond-Born-Oppenheimer (BBO) adiabatic corrections [J. J. Lutz and J. M. Hutson, J. Mol. Spectrosc. 330, 43 (2016)] and by partially treating the nonadiabatic effects using distance-dependent reduced masses. Our BBO interaction model represents the experimental data to within about 30.2 kHz on average, which is 3.7 times better than the “reference” Born-Oppenheimer model. We calculate the s-wave scattering lengths for bosonic isotopic pairs of ytterbium atoms with error bars over two orders of magnitude smaller than previous determinations. For example, the s-wave scattering length for Yb174 is +5.55812(50) nm.

Yosuke Takasu, Yoshiaki Fukushima, Yusuke Nakamura, and Yoshiro Takahashi,
Magnetoassociation of a Feshbach molecule and spin-orbit interaction between the ground and electronically,
Physical Review A 96, 023602 (2017).

[Summary] By preparing a cold-atom ensemble of mixtures of the ground 1S0 and metastable 3P2 states of ytterbiumatoms 171Yb, we successfully associate a Feshbach molecule 171Yb2 with one 171Yb atom in its electronically excited state and another one in the ground state, by sweeping a magnetic field across a Feshbach resonance. The atom-molecule conversion efficiency reaches about 50%, confirmed by a separate image of atoms and molecules with a Stern-Gerlach effect and an atom loss measurement. In addition, we successfully implement a spin-orbit coupling with a one-photon process between the 3P2 (pseudo-spin-up) and ground 1S0 (pseudo-spin-down) states of a Yb atom. As a benchmark, we observe a spin-momentum locking behavior at a large Rabi frequency. The achieved successful production of Feshbach molecules, along with the implementation of spin-orbital coupling between the 1S0 and 3P2 states, provides an important step towards the study of a topological superfluid.