1,193 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
Quantitative test of thermal field theory for Bose-Einstein condensates II
We have recently derived a gapless theory of the linear response of a
Bose-condensed gas to external perturbations at finite temperature and used it
to explain quantitatively the measurements of condensate excitations and decay
rates made at JILA [D. S. Jin et.al., Phys. Rev. Lett. 78, 764 (1997)]. The
theory describes the dynamic coupling between the condensate and non-condensate
via a full quasiparticle description of the time-dependent normal and anomalous
averages and includes all Beliaev and Landau processes. In this paper we
provide a full discussion of the numerical calculations and a detailed analysis
of the theoretical results in the context of the JILA experiment. We provide
unambiguous proof that the dipole modes are obtained accurately within our
calculations and present quantitative results for the relative phase of the
oscillations of the condensed and uncondensed atom clouds. One of the main
difficulties in the implementation of the theory is obtaining results which are
not sensitive to basis cutoff effects and we have therefore developed a novel
asymmetric summation method which solves this problem and dramatically improves
the numerical convergence. This new technique should make the implementation of
the theory and its possible future extensions feasible for a wide range of
condensate populations and trap geometries.Comment: 23 pages, 11 figures, revtex 4. Submitted to PRA. Sequel to: S. A.
Morgan et al, PRL, 91, 250403 (2003
Supporting Tropos concepts in Agent OPEN
The growth of interest in agent-orientation as a new paradigm has introduced the need for developing concepts, tools and techniques for modeling and engineering agent-based software systems. Object technology has been supporting the development of information systems for many years but is now slowly evolving to encompass more recent ideas relating to the concept of "agent". Integrating agent concepts into existing OO methodologies has resulted in several agent-oriented methodologies, one of which is Agent OPEN. In this paper, we evaluate the existing Agent OPEN description against ideas formulated within Tropos, an agent-oriented software development methodology. © Springer-Verlag Berlin Heidelberg 2004
Momentum distribution and condensate fraction of a Fermi gas in the BCS-BEC crossover
By using the diffusion Monte Carlo method we calculate the one- and two-body
density matrix of an interacting Fermi gas at T=0 in the BCS-BEC crossover.
Results for the momentum distribution of the atoms, as obtained from the
Fourier transform of the one-body density matrix, are reported as a function of
the interaction strength. Off-diagonal long-range order in the system is
investigated through the asymptotic behavior of the two-body density matrix.
The condensate fraction of fermionic pairs is calculated in the unitary limit
and on both sides of the BCS-BEC crossover.Comment: 4 pages, 4 figure
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
The critical temperature of a trapped, weakly interacting Bose gas
We report on measurements of the critical temperature of a harmonically
trapped, weakly interacting Bose gas as a function of atom number. Our results
exclude ideal-gas behavior by more than two standard deviations, and agree
quantitatively with mean-field theory. At our level of sensitivity, we find no
additional shift due to critical fluctuations. In the course of this
measurement, the onset of hydrodynamic expansion in the thermal component has
been observed. Our thermometry method takes this feature into account.Comment: version 2, 20 octobre 200
Released momentum distribution of a Fermi gas in the BCS-BEC crossover
We develop a time-dependent mean-field theory to investigate the released
momentum distribution and the released energy of an ultracold Fermi gas in the
BCS-BEC crossover after the scattering length has been set to zero by a fast
magnetic-field ramp. For a homogeneous gas we analyze the non-equilibrium
dynamics of the system as a function of the interaction strength and of the
ramp speed. For a trapped gas the theoretical predictions are compared with
experimental results.Comment: 4 pages, 4 figure
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