10 research outputs found
Velocity-dependent quantum phase slips in 1D atomic superfluids
Quantum phase slips are the primary excitations in one-dimensional
superfluids and superconductors at low temperatures but their existence in
ultracold quantum gases has not been demonstrated yet. We now study
experimentally the nucleation rate of phase slips in one-dimensional
superfluids realized with ultracold quantum gases, owing along a periodic
potential. We observe a crossover between a regime of temperature-dependent
dissipation at small velocity and interaction and a second regime of
velocity-dependent dissipation at larger velocity and interaction. This
behavior is consistent with the predicted crossover from thermally-assisted
quantum phase slips to purely quantum phase slips.Comment: 7 pages, 6 figure
Experimental observation of curved light-cones in a quantum field simulator
We investigate signal propagation in a quantum field simulator of the Klein–Gordon model realized by two strongly coupled parallel one-dimensional quasi-condensates. By measuring local phononic fields after a quench, we observe the propagation of correlations along sharp light-cone fronts. If the local atomic density is inhomogeneous, these propagation fronts are curved. For sharp edges, the propagation fronts are reflected at the system’s boundaries. By extracting the space-dependent variation of the front velocity from the data, we find agreement with theoretical predictions based on curved geodesics of an inhomogeneous metric. This work extends the range of quantum simulations of nonequilibrium field dynamics in general space–time metrics
Decay and recurrence of non-Gaussian correlations in a quantum many-body system
Gaussian models provide an excellent effective description of many quantum many-body systems ranging from condensed-matter systems1,2 all the way to neutron stars3. Gaussian states are common at equilibrium when the interactions are weak. Recently it was proposed that they can also emerge dynamically from a non-Gaussian initial state evolving under non-interacting dynamics4,5,6,7,8,9,10,11. Here we present the experimental observation of such a dynamical emergence of Gaussian correlations in a quantum many-body system. This non-equilibrium evolution is triggered by abruptly switching off the effective interaction between the observed collective degrees of freedom, while leaving the interactions between the microscopic constituents unchanged. Starting from highly non-Gaussian correlations, consistent with the sine–Gordon model12, we observe a Gaussian state emerging over time as revealed by the decay of the fourth- and sixth-order connected correlations in the quantum field. A description of this dynamics requires a novel mechanism for the emergence of Gaussian correlations, which is relevant for a wide class of quantum many-body systems. In our closed system with non-interacting effective degrees of freedom, we do not expect full thermalization13,14,15,16,17,18,19. This memory of the initial state is confirmed by observing recurrences20 of non-Gaussian correlations
Mechanisms for the emergence of Gaussian correlations
We comprehensively investigate two distinct mechanisms leading to memory loss
of non-Gaussian correlations after switching off the interactions in an
isolated quantum system undergoing out-of-equilibrium dynamics. The first
mechanism is based on spatial scrambling and results in the emergence of
locally Gaussian steady states in large systems evolving over long times. The
second mechanism, characterized as `canonical transmutation', is based on the
mixing of a pair of canonically conjugate fields, one of which initially
exhibits non-Gaussian fluctuations while the other is Gaussian and dominates
the dynamics, resulting in the emergence of relative Gaussianity even at finite
system sizes and times. We evaluate signatures of the occurrence of the two
candidate mechanisms in a recent experiment that has observed Gaussification in
an atom-chip controlled ultracold gas and elucidate evidence that it is
canonical transmutation rather than spatial scrambling that is responsible for
Gaussification in the experiment. Both mechanisms are shown to share the common
feature that the Gaussian correlations revealed dynamically by the quench are
already present though practically inaccessible at the initial time. On the
way, we present novel observations based on the experimental data,
demonstrating clustering of equilibrium correlations, analyzing the dynamics of
full counting statistics, and utilizing tomographic reconstructions of quantum
field states. Our work aims at providing an accessible presentation of the
potential of atom-chip experiments to explore fundamental aspects of quantum
field theories in quantum simulations
Experimental Observation of Curved Light-Cones in a Quantum Field Simulator
We investigate signal propagation in a quantum field simulator of the
Klein-Gordon model realized by two strongly coupled parallel one-dimensional
quasi-condensates. By measuring local phononic fields after a quench, we
observe the propagation of correlations along sharp light-cone fronts. If the
local atomic density is inhomogeneous, these propagation fronts are curved. For
sharp edges, the propagation fronts are reflected at the system's boundaries.
By extracting the space-dependent variation of the front velocity from the
data, we find agreement with theoretical predictions based on curved geodesics
of an inhomogeneous metric. This work extends the range of quantum simulations
of non-equilibrium field dynamics in general spacetime metrics.Comment: 19 pages, 12 figure
Mechanisms for the emergence of Gaussian correlations
We comprehensively investigate two distinct mechanisms leading to memory loss of non-Gaussian correlations after switching off the interactions in an isolated quantum system undergoing out-of-equilibrium dynamics. The first mechanism is based on spatial scrambling and results in the emergence of locally Gaussian steady states in large systems evolving over long times. The second mechanism, characterized as `canonical transmutation', is based on the mixing of a pair of canonically conjugate fields, one of which initially exhibits non-Gaussian fluctuations while the other is Gaussian and dominates the dynamics, resulting in the emergence of relative Gaussianity even at finite system sizes and times. We evaluate signatures of the occurrence of the two candidate mechanisms in a recent experiment that has observed Gaussification in an atom-chip controlled ultracold gas and elucidate evidence that it is canonical transmutation rather than spatial scrambling that is responsible for Gaussification in the experiment. Both mechanisms are shown to share the common feature that the Gaussian correlations revealed dynamically by the quench are already present though practically inaccessible at the initial time. On the way, we present novel observations based on the experimental data, demonstrating clustering of equilibrium correlations, analyzing the dynamics of full counting statistics, and utilizing tomographic reconstructions of quantum field states. Our work aims at providing an accessible presentation of the potential of atom-chip experiments to explore fundamental aspects of quantum field theories in quantum simulations
Designing arbitrary one-dimensional potentials on an atom chip
International audienceWe use laser light shaped by a digital micro-mirror device to realize arbitrary optical dipole potentials for one-dimensional (1D) degenerate Bose gases of 87 Rb trapped on an atom chip. Superposing optical and magnetic potentials combines the high flexibility of optical dipole traps with the advantages of magnetic trapping, such as effective evaporative cooling and the application of radio-frequency dressed state potentials. As applications, we present a 160 µm long box-like potential with a central tuneable barrier, a box-like potential with a sinusoidally modulated bottom and a linear confining potential. These potentials provide new tools to investigate the dynamics of 1D quantum systems and will allow us to address exciting questions in quantum thermodynamics and quantum simulations