Observation of the Mott Insulator to Superfluid Crossover of a Driven-Dissipative Bose-Hubbard System

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 preparation and manipulation of quantum states. Here 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 photo-association 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 non-equilibrium dynamics.Comment: 26 pages, 17 figure

Glycocalyx Degradation in Retinal and Choroidal Capillary Endothelium in Rats with Diabetes and Hypertension

Endothelial glycocalyx (GCX) has been reported as a protective factor for vascular endothelial cells (VEC) in diabetes and hypertension. However, the involvement of GCX impairment in ocular vasculopathy remains unclear. We evaluated the changes in the GCX thicknesses of the retinal and choroidal capillaries in rats with diabetes and hypertension by cationic colloidal iron staining using a transmission electron microscope. In the control group, the mean (standard error of the mean) thicknesses of retinal and choroidal GCX were 60.2 (1.5) nm and 84.3 (3.1) nm, respectively. The diabetic rats showed a significant decrease of GCX thickness in the retina, but not in the choroid, compared to controls (28.3 (0.3) nm, p＜0.01 and 77.8 (1.4) nm, respectively). In the hypertensive rats, both retinal and choroidal GCX were significantly decreased compared to the control values (10.9 (0.4) nm and 13.2 (1.0) nm, respectively, both p＜0.01). Moreover, we could visualize the adhesion of leukocytes and platelets on the luminal surface of VEC, at the site where the GCX was markedly degraded. These findings suggest that the GCX prevents adhesion of leukocytes and platelets to the VEC surface, and this impairment may lead to ocular vasculopathy in diabetes and hypertension

SU(3) truncated Wigner approximation for strongly interacting Bose gases

We develop and utilize the SU(3) truncated Wigner approximation (TWA) in order to analyze far-from-equilibrium quantum dynamics of strongly interacting Bose gases in an optical lattice. Specifically, we explicitly represent the corresponding Bose--Hubbard model at an arbitrary filling factor with restricted local Hilbert spaces in terms of SU(3) matrices. Moreover, we introduce a discrete Wigner sampling technique for the SU(3) TWA and examine its performance as well as that of the SU(3) TWA with the Gaussian approximation for the continuous Wigner function. We directly compare outputs of these two approaches with exact computations regarding dynamics of the Bose--Hubbard model at unit filling with a small size and that of a fully-connected spin-1 model with a large size. We show that both approaches can quantitatively capture quantum dynamics on a timescale of $\hbar/(Jz)$, where $J$ and $z$ denote the hopping energy and the coordination number. We apply the two kinds of SU(3) TWA to dynamical spreading of a two-point correlation function of the Bose--Hubbard model on a square lattice with a large system size, which has been measured in recent experiments. Noticeable deviations between the theories and experiments indicate that proper inclusion of effects of the spatial inhomogeneity, which is not straightforward in our formulation of the SU(3) TWA, may be necessary.Comment: 21 pages, 8 figure

Energy redistribution and spatio-temporal evolution of correlations after a sudden quench of the Bose-Hubbard model

An optical-lattice quantum simulator is an ideal experimental platform to investigate non-equilibrium dynamics of a quantum many-body system, which is in general hard to simulate with classical computers. Here, we use our quantum simulator of the Bose-Hubbard model to study dynamics far from equilibrium after a quantum quench. We successfully confirm the energy conservation law in the one- and three-dimensional systems and extract the propagation velocity of the single-particle correlation in the one- and two-dimensional systems. We corroborate the validity of our quantum simulator through quantitative comparisons between the experiments and the exact numerical calculations in one dimension. In the computationally hard cases of two or three dimensions, by using the quantum-simulation results as references, we examine the performance of a numerical method, namely the truncated Wigner approximation, revealing its usefulness and limitation. This work constitutes an exemplary case for the usage of analog quantum simulators.Comment: 16 pages, 11 figures (the Supplementary Materials included

Energy redistribution and spatiotemporal evolution of correlations after a sudden quench of the Bose-Hubbard model

非局所相関の伝搬の観測とエネルギー保存則の検証に成功 --冷却原子を用いた量子多体ダイナミクスの量子シミュレーション--. 京都大学プレスリリース. 2020-10-09.An optical lattice quantum simulator is an ideal experimental platform to investigate nonequilibrium dynamics of a quantum many-body system, which is, in general, hard to simulate with classical computers. Here, we use our quantum simulator of the Bose-Hubbard model to study dynamics far from equilibrium after a quantum quench. We successfully confirm the energy conservation law in the one- and three-dimensional systems and extract the propagation velocity of the single-particle correlation in the one- and two-dimensional systems. We corroborate the validity of our quantum simulator through quantitative comparisons between the experiments and the exact numerical calculations in one dimension. In the computationally hard cases of two or three dimensions, by using the quantum-simulation results as references, we examine the performance of a numerical method, namely, the truncated Wigner approximation, revealing its usefulness and limitation. This work constitutes an exemplary case for the usage of analog quantum simulators

Objective and quantitative estimation of the optimal timing for epiretinal membrane surgery on the basis of metamorphopsia

Purpose: To establish an objective and quantitative biomarker of metamorphopsia in epiretinal membranes (ERMs) and determine the optimal timing for ERM surgery. Methods: Retrospectively, 172 eyes with ERM were reviewed. Retinal folds due to tangential traction by ERM were visualized by en face optical coherence tomography (OCT). The maximum depth of retinal folds (MDRF) within the parafovea was quantified. Metamorphopsia was quantified by M-CHARTS. The change in the distance between the retinal vessels after ERM surgery and the preoperative total depth of retinal folds between the vessels were quantified using en face OCT and OCT angiography. Results: Significant correlations were observed between preoperative MDRF and M-CHARTS scores before and at 6 months after surgery (r=0.617 and 0.460, respectively; P Conclusion: MDRF is an objective and quantitative biomarker of metamorphopsia in ERM. To maintain patients’ quality of vision, ERM surgery may be performed when the preoperative MDRF ranges between 69 and 118 μm