1,325 research outputs found

### Phase separation in a polarized Fermi gas at zero temperature

We investigate the phase diagram of asymmetric two-component Fermi gases at
zero temperature as a function of polarization and interaction strength. The
equations of state of the uniform superfluid and normal phase are determined
using quantum Monte Carlo simulations. We find three different mixed states,
where the superfluid and the normal phase coexist in equilibrium, corresponding
to phase separation between: (a) the polarized superfluid and the fully
polarized normal gas, (b) the polarized superfluid and the partially polarized
normal gas and (c) the unpolarized superfluid and the partially polarized
normal gas.Comment: 4 pages, 4 figures, revised, accepted for publication in Phys. Rev.
Let

### BCS-BEC crossover in a two-dimensional Fermi gas

We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS)
superfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi
gas at T=0 using the fixed-node diffusion Monte Carlo method. We calculate the
equation of state and the gap parameter as a function of the interaction
strength, observing large deviations compared to mean-field predictions. In the
BEC regime our results show the important role of dimer-dimer and atom-dimer
interaction effects that are completely neglected in the mean-field picture.
Results on Tan's contact parameter associated with short-range physics are also
reported along the BCS-BEC crossover.Comment: 4 pages, 4 figure

### Liquid and crystal phase of dipolar fermions in two dimensions

The liquid and crystal phase of a single-component Fermi gas with dipolar
interactions are investigated using quantum Monte Carlo methods in two spatial
dimensions and at zero temperature. The dipoles are oriented by an external
field perpendicular to the plane of motion, resulting in a purely repulsive
1/r^3 interaction. In the liquid phase we calculate the equation of state as a
function of the interaction strength and other relevant properties
characterizing the Fermi-liquid behavior: effective mass, discontinuity at the
Fermi surface and pair correlation function. In the high density regime we
calculate the equation of state of the Wigner crystal phase and the critical
density of the liquid to solid first order phase transition. Close to the
freezing density we also search for the existence of a stripe phase, but such a
phase is never found to be energetically favorable.Comment: 5 pages, 5 figure

### Molecular signatures in the structure factor of an interacting Fermi gas

The static and dynamic structure factors of an interacting Fermi gas along
the BCS-BEC crossover are calculated at momentum transfer $\hbar{\bf k}$ higher
than the Fermi momentum. The spin structure factor is found to be very
sensitive to the correlations associated with the formation of molecules. On
the BEC side of the crossover, even close to unitarity, clear evidence is found
for a molecular excitation at $\hbar^2 k^2 /4m$, where $m$ is the atomic mass.
Both quantum Monte Carlo and dynamic mean-field results are presented.Comment: 4 pages, 4 figure

### Density profiles of polarized Fermi gases confined in harmonic traps

On the basis of the phase diagram of the uniform system we calculate the
density profiles of a trapped polarized Fermi gas at zero temperature using the
local density approximation. By varying the overall polarization and the
interaction strength we analyze the appearance of a discontinuity in the
profile, signalling a first order phase transition from a superfluid inner core
to a normal outer shell. The local population imbalance between the two
components and the size of the various regions of the cloud corresponding to
different phases are also discussed. The calculated profiles are quantitatively
compared with the ones recently measured by Shin {\it et al.}, Phys. Rev. Lett.
{\bf 101}, 070404 (2008).Comment: 6 pages, 4 figures. We added references and modified the figure

### The Bose polaron problem: effect of mass imbalance on binding energy

By means of Quantum Monte Carlo methods we calculate the binding energy of an
impurity immersed in a Bose-Einstein condensate at T = 0. The focus is on the
attractive branch of the Bose polaron and on the role played by the mass
imbalance between the impurity and the surrounding particles. For an impurity
resonantly coupled to the bath, we investigate the dependence of the binding
energy on the mass ratio and on the interaction strength within the medium. In
particular, we determine the equation of state in the case of a static
(infinite mass) impurity, where three-body correlations are irrelevant and the
result is expected to be a universal function of the gas parameter. For the
mass ratio corresponding to $^{40}$K impurities in a gas of $^{87}$Rb atoms we
provide an explicit comparison with the experimental findings of a recent study
carried out at JILA.Comment: 5 pages, 3 figure

### Quantum Monte Carlo simulation of a two-dimensional Bose gas

The equation of state of a homogeneous two-dimensional Bose gas is calculated
using quantum Monte Carlo methods. The low-density universal behavior is
investigated using different interatomic model potentials, both finite-ranged
and strictly repulsive and zero-ranged supporting a bound state. The condensate
fraction and the pair distribution function are calculated as a function of the
gas parameter, ranging from the dilute to the strongly correlated regime. In
the case of the zero-range pseudopotential we discuss the stability of the
gas-like state for large values of the two-dimensional scattering length, and
we calculate the critical density where the system becomes unstable against
cluster formation.Comment: 6 pages, 5 figures, 1 tabl

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