215 research outputs found
Pressure, compressibility, and contact of the two-dimensional attractive Fermi gas
Using ab initio lattice methods, we calculate the finite temperature
thermodynamics of homogeneous two-dimensional spin-1/2 fermions with attractive
short-range interactions. We present results for the density, pressure,
compressibility, and quantum anomaly (i.e. Tan's contact) for a wide range of
temperatures and coupling strengths, focusing on the unpolarized case. Within
our statistical and systematic uncertainties, our prediction for the density
equation of state differs quantitatively from the prediction by Luttinger-Ward
theory in the strongly coupled region of parameter space, but otherwise agrees
well with it. We also compare our calculations with the second- and third-order
virial expansion, with which they are in excellent agreement in the
low-fugacity regime.Comment: 7 pages, 8 figures, including supplemental material
Energy, contact, and density profiles of one-dimensional fermions in a harmonic trap via non-uniform lattice Monte Carlo
We determine the ground-state energy and Tan's contact of attractively
interacting few-fermion systems in a one-dimensional harmonic trap, for a range
of couplings and particle numbers. Complementing those results, we show the
corresponding density profiles. The calculations were performed with a new
lattice Monte Carlo approach based on a non-uniform discretization of space,
defined via Gauss-Hermite quadrature points and weights. This particular
coordinate basis is natural for systems in harmonic traps, and can be
generalized to traps of other shapes. In all cases, it yields a
position-dependent coupling and a corresponding non-uniform
Hubbard-Stratonovich transformation. The resulting path integral is performed
with hybrid Monte Carlo as a proof of principle for calculations at finite
temperature and in higher dimensions. We present results for N=4,...,20
particles (although the method can be extended beyond that) to cover the range
from few- to many-particle systems. This method is also exact up to statistical
and systematic uncertainties, which we account for -- and thus also represents
the first ab initio calculation of this system, providing a benchmark for other
methods and a prediction for ultracold-atom experiments.Comment: 13 pages, 10 figures; including supplemental materia
Dynamics of entanglement entropy of interacting fermions in a 1D driven harmonic trap
Following up on a recent analysis of two cold atoms in a time-dependent
harmonic trap in one dimension, we explore the entanglement entropy of two and
three fermions in the same situation when driven through a parametric
resonance. We find that the presence of such a resonance in the two-particle
system leaves a clear imprint on the entanglement entropy. We show how the
signal is modified by attractive and repulsive contact interactions, and how it
remains present for the three-particle system. Additionaly, we extend the work
of recent experiments to demonstrate how restricting observation to a limited
subsystem gives rise to locally thermal behavior.Comment: Proceedings of Lattice2017, Granada, Spai
Spin 1/2 Fermions in the Unitary Regime at Finite Temperature
We have performed a fully non-perturbative calculation of the thermal
properties of a system of spin 1/2 fermions in 3D in the unitary regime. We
have determined the critical temperature for the superfluid-normal phase
transition. The thermodynamic behavior of this system presents a number of
unexpected features, and we conclude that spin 1/2 fermions in the BCS-BEC
crossover should be classified as a new type of superfluid.Comment: 6 pages, 2 figures, version for the Proceedings of QMBT1
Thermodynamics of a Trapped Unitary Fermi Gas
We present the first model-independent comparison of recent measurements of
the entropy and of the critical temperature of a unitary Fermi gas, performed
by Luo et al., with the most complete results currently available from finite
temperature Monte Carlo calculations. The measurement of the critical
temperature in a cold fermionic atomic cloud is consistent with a value
in the bulk, as predicted by the present authors in
their Monte Carlo calculations.Comment: 5 pages, 4 figures, published versio
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