85 research outputs found
Interaction induced phase fluctuations in a guided atom laser
In this paper, we determine the magnitude of phase fluctuations caused by
atom-atom interaction in a one-dimensional beam of bosonic atoms. We imagine
that the beam is created with a large coherence length, and that interactions
only act in a specific section of the beam, where the atomic density is high
enough to validate a Bogoliubov treatment. The magnitude and coherence length
of the ensuing phase fluctuations in the beam after the interaction zone are
determined.Comment: 5 pages, 2 figure
Relative phase fluctuations of two coupled one-dimensional condensates
We study the relative phase fluctuations of two one-dimensional condensates coupled along their whole extension with a local single-atom interaction. The thermal equilibrium is defined by the competition between independent longitudinal thermally excited phase fluctuations and the coupling between the condensates which locally favors identical phase. We compute the relative phase fluctuations and their correlation length as a function of the temperature and the strength of the coupling
Monitoring squeezed collective modes of a one-dimensional Bose gas after an interaction quench using density ripples analysis
We investigate the out-of-equilibrium dynamics following a sudden quench of
the interaction strength, in a one-dimensional quasi-condensate trapped at the
surface of an atom chip. Within a linearized approximation, the system is
described by independent collective modes and the quench squeezes the phase
space distribution of each mode, leading to a subsequent breathing of each
quadrature. We show that the collective modes are resolved by the power
spectrum of density ripples which appear after a short time of flight. This
allows us to experimentally probe the expected breathing phenomenon. Our
results are in good agreement with theoretical predictions which take the
longitudinal harmonic confinement into account
Generalized HydroDynamics on an Atom Chip
The emergence of a special type of fluid-like behavior at large scales in
one-dimensional (1d) quantum integrable systems, theoretically predicted in
2016, is established experimentally, by monitoring the time evolution of the in
situ density profile of a single 1d cloud of atoms trapped on
an atom chip after a quench of the longitudinal trapping potential. The theory
can be viewed as a dynamical extension of the thermodynamics of Yang and Yang,
and applies to the whole range of repulsion strength and temperature of the
gas. The measurements, performed on weakly interacting atomic clouds that lie
at the crossover between the quasicondensate and the ideal Bose gas regimes,
are in very good agreement with the 2016 theory. This contrasts with the
previously existing 'conventional' hydrodynamic approach---that relies on the
assumption of local thermal equilibrium---, which is unable to reproduce the
experimental data.Comment: v1: 6+11 pages, 4+4 figures. v2: published version, 6+11 pages, 4+6
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Long-lived non-thermal states realized by atom losses in one-dimensional quasi-condensates
We investigate the cooling produced by a loss process non selective in energy
on a one-dimensional (1D) Bose gas with repulsive contact interactions in the
quasi-condensate regime. By performing nonlinear classical field calculations
for a homogeneous system, we show that the gas reaches a non-thermal state
where different modes have acquired different temperatures. After losses have
been turned off, this state is robust with respect to the nonlinear dynamics,
described by the Gross-Pitaevskii equation. We argue that the integrability of
the Gross-Pitaevskii equation is linked to the existence of such long-lived
non-thermal states, and illustrate this by showing that such states are not
supported within a non-integrable model of two coupled 1D gases of different
masses. We go beyond a classical field analysis, taking into account the
quantum noise introduced by the discreteness of losses, and show that the
non-thermal state is still produced and its non-thermal character is even
enhanced. Finally, we extend the discussion to gases trapped in a harmonic
potential and present experimental observations of a long-lived non-thermal
state within a trapped 1D quasi-condensate following an atom loss process
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