1,119 research outputs found
Quantum Monte Carlo Study of a Resonant Bose-Fermi Mixture
We study a resonant Bose-Fermi mixture at zero temperature by using the
fixed-node diffusion Monte Carlo method. We explore the system from weak to
strong boson-fermion interaction, for different concentrations of the bosons
relative to the fermion component. We focus on the case where the boson density
is smaller than the fermion density , for which a first-order
quantum phase transition is found from a state with condensed bosons immersed
in a Fermi sea, to a Fermi-Fermi mixture of composite fermions and unpaired
fermions. We obtain the equation of state and the phase diagram, and we find
that the region of phase separation shrinks to zero for vanishing .Comment: 5 pages, 3 figures, published versio
Self-contained breathing apparatus
A self-contained breathing apparatus with automatic redundant fluid pressure controls and a facemask mounted low pressure whistle alarm is described. The first stage of the system includes pair of pressure regulators connected in parallel with different outlet pressures, both of which reduce the pressure of the stored supply gas to pressures compatible with the second stage breathing demand regulator. A primary regulator in the first stage delivers a low output pressure to the demand regulator. In the event of a failure closed condition of the primary regulator an automatic transfer valve switches on the backup regulator. A warning that the supply pressure has been depleted is also provided by a supply pressure actuated transfer valve which transfers the output of the first stage pressure regulators from the primary to the backup regulator. The alarm is activated in either the failure closed condition or if the supply pressure is reduced to a dangerously low level
Single-particle vs. pair superfluidity in a bilayer system of dipolar bosons
We consider the ground state of a bilayer system of dipolar bosons, where
dipoles are oriented by an external field in the direction perpendicular to the
parallel planes. Quantum Monte Carlo methods are used to calculate the
ground-state energy, the one-body and two-body density matrix, and the
superfluid response as a function of the separation between layers. We find
that by decreasing the interlayer distance for fixed value of the strength of
the dipolar interaction, the system undergoes a quantum phase transition from a
single-particle to a pair superfluid. The single-particle superfluid is
characterized by a finite value of both the atomic condensate and the
super-counterfluid density. The pair superfluid phase is found to be stable
against formation of many-body cluster states and features a gap in the
spectrum of elementary excitations.Comment: 4 figure
Beyond Tonks-Girardeau: strongly correlated regime in quasi-one-dimensional Bose gases
We consider a homogeneous 1D Bose gas with contact interactions and large
attractive coupling constant. This system can be realized in tight waveguides
by exploiting a confinement induced resonance of the effective 1D scattering
amplitude. By using a variational {\it ansatz} for the many-body wavefunction,
we show that for small densities the gas-like state is stable and the
corresponding equation of state is well described by a gas of hard rods. By
calculating the compressibility of the system, we provide an estimate of the
critical density at which the gas-like state becomes unstable against cluster
formation. Within the hard-rod model we calculate the one-body density matrix
and the static structure factor of the gas. The results show that in this
regime the system is more strongly correlated than a Tonks-Girardeau gas. The
frequency of the lowest breathing mode for harmonically trapped systems is also
discussed as a function of the interaction strength.Comment: 4 pages, 4 figure
Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures
We calculate the shift in the critical temperature of Bose-Einstein
condensation for a dilute Bose-Fermi mixture confined by a harmonic potential
to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The
relative importance of the effect on the critical temperature of the
boson-boson and boson-fermion interactions is investigated as a function of the
parameters of the mixture. The possible relevance of the shift of the
transition temperature in current experiments on trapped Bose-Fermi mixtures is
discussed.Comment: 15 pages, 2 figures, submitted to J. Phys.
Equation of state of a Fermi gas in the BEC-BCS crossover: a quantum Monte Carlo study
We calculate the equation of state of a two-component Fermi gas with
attractive short-range interspecies interactions using the fixed-node diffusion
Monte Carlo method. The interaction strength is varied over a wide range by
tuning the value of the s-wave scattering length of the two-body potential.
For and smaller than the inverse Fermi wavevector our results show a
molecular regime with repulsive interactions well described by the dimer-dimer
scattering length . The pair correlation functions of parallel and
opposite spins are also discussed as a function of the interaction strength.Comment: 4 pages, 3 figures. Version accepted for publication in Phys. Rev.
Lett.. Figure 3 removed. Expanded discussion of correlation functions. New
figure 4. Calculation of pair correlation functions improved: more statistics
and extrapolation technique to remove residual dependences on the trial wave
function. Added comparison with Bogoliubov theory. References adde
Quasi-one-dimensional Bose gases with large scattering length
Bose gases confined in highly-elongated harmonic traps are investigated over
a wide range of interaction strengths using quantum Monte Carlo techniques. We
find that the properties of a Bose gas under tight transverse confinement are
well reproduced by a 1d model Hamiltonian with contact interactions. We point
out the existence of a unitary regime, where the properties of the quasi-1d
Bose gas become independent of the actual value of the 3d scattering length. In
this unitary regime, the energy of the system is well described by a hard rod
equation of state. We investigate the stability of quasi-1d Bose gases with
positive and negative 3d scattering length.Comment: 5 pages, 3 figure
Correlation functions of a Lieb-Liniger Bose gas
The ground-state correlation functions of a one-dimensional homogeneous Bose
system described by the Lieb-Liniger Hamiltonian are investigated by using
exact quantum Monte Carlo techniques. This article is an extension of a
previous study published in Phys. Rev. A {\bf 68}, 031602 (2003). New results
on the local three-body correlator as a function of the interaction strength
are included and compared with the measured value from three-body loss
experiments. We also carry out a thorough study of the short- and long-range
behavior of the one-body density matrix.Comment: 10 pages, 8 figures, contribution to Cortona BEC JPB special issu
Anomalous fluctuations of the condensate in interacting Bose gases
We find that the fluctuations of the condensate in a weakly interacting Bose
gas confined in a box of volume follow the law . This anomalous behaviour arises from the occurrence of infrared
divergencies due to phonon excitations and holds also for strongly correlated
Bose superfluids. The analysis is extended to an interacting Bose gas confined
in a harmonic trap where the fluctuations are found to exhibit a similar
anomaly.Comment: 4 pages, RevTe
- …