22 research outputs found
How to measure the free energy and partition function from atom-atom correlations
We propose an experimental approach for determining thermodynamic properties
of ultracold atomic gases with short-range interactions. As a test case, we
focus on the one-dimensional (1D) Bose gas described by the integrable
Lieb-Liniger model. The proposed approach relies on deducing the Helmholtz or
Landau free energy directly from measurements of local atom-atom correlations
by utilising the inversion of a finite-temperature version of the
Hellmann-Feynman theorem. We demonstrate this approach theoretically by
deriving approximate analytic expressions for the free energies in specific
asymptotic regimes of the 1D Bose gas and find excellent agreement with the
exact results based on the thermodynamic Bethe ansatz available for this
integrable model.Comment: 8 pages, 3 figure
Spectral, noise and correlation properties of intense squeezed light generated by a coupling in two laser fields
Two schemes of four-wave mixing oscillators with nondegenerate pumps are proposed for above-threehold generation of squeezed light with nonzero mean-field amplitudes. Noise and correlation properties and optical spectra of squeezed-light beams generated in these schemes are discussed
Relaxation dynamics of the Lieb-Liniger gas following an interaction quench: A coordinate Bethe-ansatz analysis
We investigate the relaxation dynamics of the integrable Lieb-Liniger model
of contact-interacting bosons in one dimension following a sudden quench of the
collisional interaction strength. The system is initially prepared in its
noninteracting ground state and the interaction strength is then abruptly
switched to a positive value, corresponding to repulsive interactions between
the bosons. We calculate equal-time correlation functions of the nonequilibrium
Bose field for small systems of up to five particles via symbolic evaluation of
coordinate Bethe-ansatz expressions for operator matrix elements between
Lieb-Liniger eigenstates. We characterize the relaxation of the system by
comparing the time-evolving correlation functions following the quench to the
equilibrium correlations predicted by the diagonal ensemble and relate the
behavior of these correlations to that of the quantum fidelity between the
many-body wave function and the initial state of the system. Our results for
the asymptotic scaling of local second-order correlations with increasing
interaction strength agree with the predictions of recent generalized
thermodynamic Bethe-ansatz calculations. By contrast, third-order correlations
obtained within our approach exhibit a markedly different power-law dependence
on the interaction strength as the Tonks-Girardeau limit of infinitely strong
interactions is approached.Comment: 19 pages, 10 figures. v3: Final version. Typos fixed, and other minor
change
Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance
We report the experimental realization of a single-species atomic four-wave
mixing process with BEC collisions for which the angular distribution of
scattered atom pairs is not isotropic, despite the collisions being in the
-wave regime. Theoretical analysis indicates that this anomalous behavior
can be explained by the anisotropic nature of the gain in the medium. There are
two competing anisotropic processes: classical trajectory deflections due to
the mean-field potential, and Bose enhanced scattering which bears similarity
to super-radiance. We analyse the relative importance of these processes in the
dynamical buildup of the anisotropic density distribution of scattered atoms,
and compare to optically pumped super-radiance.Comment: 13 pages, 10 figures, added a fuller discussion of timescales,
otherwise some minor changes in the text and the formatting of Figures 5-
Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics
We experimentally demonstrate a nonlinear detection scheme exploiting
time-reversal dynamics that disentangles continuous variable entangled states
for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is
used as the nonlinear mechanism which not only generates entangled states but
can also be time reversed by controlled phase imprinting. For demonstration of
a quantum-enhanced measurement we construct an active atom SU(1,1)
interferometer, where entangled state preparation and nonlinear readout both
consist of parametric amplification. This scheme is capable of exhausting the
quantum resource by detecting solely mean atom numbers. Controlled nonlinear
transformations widen the spectrum of useful entangled states for applied
quantum technologies.Comment: 9 pages, 3 figures, 3 pages supplementary material, 2 supplementary
figure
Frequency beating and damping of breathing oscillations of a harmonically trapped one-dimensional quasicondensate
We study the breathing (monopole) oscillations and their damping in a
harmonically trapped one-dimensional (1D) Bose gas in the quasicondensate
regime using a finite-temperature classical field approach. By characterizing
the oscillations via the dynamics of the density profile's rms width over long
time, we find that the rms width displays beating of two distinct frequencies.
This means that 1D Bose gas oscillates not at a single breathing mode
frequency, as found in previous studies, but as a superposition of two distinct
breathing modes, one oscillating at frequency close to
and the other at , where is the trap frequency. The
breathing mode at dominates the beating at lower
temperatures, deep in the quasicondensate regime, and can be attributed to the
oscillations of the bulk of the density distribution comprized of particles
populating low-lying, highly-occupied states. The breathing mode at
, on the other hand, dominates the beating at higher
temperatures, close to the nearly ideal Bose gas regime, and is attributed to
the oscillations of the tails of the density distribution comprized of thermal
particles in higher energy states. The two breathing modes have distinct
damping rates, with the damping rate of the bulk component being an order of
magnitude larger than that of the tails component, and at least 2--3 times
smaller than the damping rate predicted by Landau's theory of damping in 1D.Comment: 11 pages, 8 figure
Sub-Poissonian number differences in four-wave mixing of matter waves
We demonstrate sub-Poissonian number differences in four-wave mixing of
Bose-Einstein condensates of metastable helium. The collision between two
Bose-Einstein condensates produces a scattering halo populated by pairs of
atoms of opposing velocities, which we divide into several symmetric zones. We
show that the atom number difference for opposing zones has sub-Poissonian
noise fluctuations whereas that of nonopposing zones is well described by shot
noise. The atom pairs produced in a dual number state are well adapted to sub
shot-noise interferometry and studies of Einstein-Podolsky-Rosen-type
nonlocality tests.Comment: 4 pages, 3 figure