20 research outputs found
Response of the Higgs amplitude mode of superfluid Bose gases in a three dimensional optical lattice
We study the Higgs mode of superfluid Bose gases in a three dimensional
optical lattice, which emerges near the quantum phase transition to the Mott
insulator at commensurate fillings. Specifically, we consider responses of the
Higgs mode to temporal modulations of the onsite interaction and the hopping
energy. In order to calculate the response functions including the effects of
quantum and thermal fluctuations, we map the Bose-Hubbard model onto an
effective pseudospin-one model and use a perturbative expansion based on the
imaginary-time Green's function theory. We also include the effects of an
inhomogeneous trapping potential by means of a local density approximation. We
find that the response function for the hopping modulation is equal to that for
the interaction modulation within our approximation. At the unit filling rate
and in the absence of a trapping potential, we show that the Higgs mode can
exist as a sharp resonance peak in the dynamical susceptibilities at typical
temperatures. However, the resonance peak is significantly broadened due to the
trapping potential when the modulations are applied globally to the entire
system. We suggest that the Higgs mode can be detected as a sharp resonance
peak by partial modulations around the trap center.Comment: 22 pages, 9 figure
Semiclassical dynamics of a dark soliton in a one-dimensional bosonic superfluid in an optical lattice
We study quantum dynamics of a dark soliton in a one-dimensional Bose gas in
an optical lattice within the truncated Wigner approximation. A previous work
has revealed that in the absence of quantum fluctuations, dynamical stability
of the dark soliton significantly depends on whether its phase kink is located
at a lattice site or a link of two neighboring sites. It has also shown that
the dark soliton is unstable in a regime of strong quantum fluctuations
regardless of the phase-kink position. To bridge the gap between the classical
and strongly quantum regimes, we investigate the dynamical stability of the
dark soliton in a regime of weak quantum fluctuations. We find that the
position dependence of the dynamical stability gradually diminishes and
eventually vanishes as the strength of quantum fluctuations increases. This
classical-to-quantum crossover of the soliton stability remains even in the
presence of a parabolic trapping potential. We suggest that the crossover
behavior can be used for experimentally diagnosing whether the instability of a
dark soliton is due to quantum fluctuations or classical dynamical instability.Comment: 12 pages, 11 figure
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 ,
where and 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
Performance evaluation of the discrete truncated Wigner approximation for quench dynamics of quantum spin systems with long-range interactions
The discrete truncated Wigner approximation (DTWA) is a powerful tool for
analyzing dynamics of quantum spin systems. Since the DTWA includes the
leading-order quantum corrections to a mean-field approximation, it is
naturally expected that the DTWA becomes more accurate when the range of
interactions of the system increases. However, quantitative corroboration of
this expectation is still lacking mainly because it is generally difficult in a
large system to evaluate a timescale on which the DTWA is quantitatively valid.
In order to investigate how the validity timescale depends on the interaction
range, we analyze dynamics of quantum spin models with a step function type
interaction subjected to a sudden quench of a magnetic field by means of both
DTWA and its extension including the second-order correction, which is derived
from the Bogoliubov-Born-Green-Kirkwood-Yvon equation. We also develop a
formulation for calculating the second-order R\'enyi entropy within the
framework of the DTWA. By comparing the time evolution of the R\'enyi entropy
computed by the DTWA with that by the extension including the correction, we
find that both in the one- and two-dimensional systems the validity timescale
increases algebraically with the range of the step function type interaction.Comment: 17 pages, 7 figure
Squamous Cell Carcinoma of the Hilar Bile Duct
We herein report a rare case of squamous cell carcinoma of the hilar bile duct. A 66-year-old Japanese male patient was admitted to our hospital because of appetite loss and jaundice. Abdominal computed tomography revealed an enhanced mass measuring 10 × 30 mm in the hilar bile duct region. After undergoing biliary drainage, the patient underwent extended right hepatic lobectomy with regional lymph nodes dissection. The tumor had invaded the right portal vein. Therefore, we also performed resection and reconstruction of the portal vein. Histopathologically, the carcinoma cells exhibited a solid structure with differentiation to squamous cell carcinoma with keratinization and intercellular bridges. Immunohistochemical staining of the tumor cells revealed positive cytokeratin staining and negative CAM 5.2 staining. Based on these findings, a definitive diagnosis of well-differentiated squamous cell carcinoma of the hilar bile duct was made
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
Modelisation et commande optimale d'un reseau de distribution d'eau potable. Mise en oeuvre, test et etudes des performances sur le reseau du FIUM'ORBO
SIGLEINIST T 70801 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc