41 research outputs found
The role of thermal fluctuations in sound propagation in a two-dimensional Fermi gas
We numerically study the transport properties of a two-dimensional Fermi gas
in a weakly and strongly interacting regimes, in the range of temperatures
close to the transition to a superfluid phase. For that we excite sound waves
in a fermionic mixture by using the phase imprinting technique, follow their
evolution, and finally determine both their speed and attenuation. Our
formalism incorporates thermal fluctuations via the ground canonical ensemble
description and with the help of Metropolis algoritm. From numerical
simulations we extract temperature dependence of the sound velocity and
diffusivity as well as the dependence on the interaction strength. We emphasize
the role of virtual vortex-antivortex pairs creation in the process of sound
dissipation
Single-shot simulations of dynamics of quantum dark solitons
Eigenstates of Bose particles with repulsive contact interactions in
one-dimensional space with periodic boundary conditions can be found with the
help of the Bethe ansatz. The type~II excitation spectrum identified by E. H.
Lieb, reproduces the dispersion relation of dark solitons in the mean-field
approach. The corresponding eigenstates possess translational symmetry which
can be broken in measurements of positions of particles. We analyze emergence
of single and double solitons in the course of the measurements and investigate
dynamics of the system. In the weak interaction limit, the system follows the
mean-field prediction for a short period of time. Long time evolution reveals
many-body effects that are related to an increasing uncertainty of soliton
positions. In the strong interaction regime particles behave like impenetrable
bosons. Then, the probability densities in the configuration space become
identical to the probabilities of non-interacting fermions but the
wave-functions themselves remember the original Bose statistics. Especially,
the phase flips that are key signatures of the solitons in the weak interaction
limit, can be observed in the time evolution of the strongly interacting
bosons.Comment: 11 pages, 9 figure
Exact dynamics and decoherence of two cold bosons in a 1D harmonic trap
We study dynamics of two interacting ultra cold Bose atoms in a harmonic
oscillator potential in one spatial dimension. Making use of the exact solution
of the eigenvalue problem of a particle in the delta-like potential we study
time evolution of initially separable state of two particles. The corresponding
time dependent single particle density matrix is obtained and diagonalized and
single particle orbitals are found. This allows to study decoherence as well as
creation of entanglement during the dynamics. The evolution of the orbital
corresponding to the largest eigenvalue is then compared to the evolution
according to the Gross-Pitaevskii equation. We show that if initially the
center of mass and relative degrees of freedom are entangled then the
Gross-Pitaevskii equation fails to reproduce the exact dynamics and
entanglement is produced dynamically. We stress that predictions of our study
can be verified experimentally in an optical lattice in the low-tunneling
limit.Comment: 9 figures, 5 movies available on-lin