Dávid X. Horváth, Spyros Sotiriadis, Márton Kormos, Gábor Takács
SciPost Phys. 12, 144 (2022) ·
published 3 May 2022
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We study inhomogeneous quantum quenches in the attractive regime of the
sine-Gordon model. In our protocol, the system is prepared in an inhomogeneous
initial state in finite volume by coupling the topological charge density
operator to a Gaussian external field. After switching off the external field,
the subsequent time evolution is governed by the homogeneous sine-Gordon
Hamiltonian. Varying either the interaction strength of the sine-Gordon model
or the amplitude of the external source field, an interesting transition is
observed in the expectation value of the soliton density. This affects both the
initial profile of the density and its time evolution and can be summarised as
a steep transition between behaviours reminiscent of the Klein-Gordon, and the
free massive Dirac fermion theory with initial external fields of high enough
magnitude. The transition in the initial state is also displayed by the
classical sine-Gordon theory and hence can be understood by semi-classical
considerations in terms of the presence of small amplitude field configurations
and the appearance of soliton excitations, which are naturally associated with
bosonic and fermionic excitations on the quantum level, respectively. Features
of the quantum dynamics are also consistent with this correspondence and
comparing them to the classical evolution of the density profile reveals that
quantum effects become markedly pronounced during the time evolution. These
results suggest a crossover between the dominance of bosonic and fermionic
degrees of freedom whose precise identification in terms of the fundamental
particle excitations can be rather non-trivial. Nevertheless, their interplay
is expected to influence the sine-Gordon dynamics in arbitrary inhomogeneous
settings.
Marek Gluza, Thomas Schweigler, Mohammadamin Tajik, João Sabino, Federica Cataldini, Frederik S. Møller, Si-Cong Ji, Bernhard Rauer, Jörg Schmiedmayer, Jens Eisert, Spyros Sotiriadis
SciPost Phys. 12, 113 (2022) ·
published 30 March 2022
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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.
SciPost Phys. 6, 004 (2019) ·
published 10 January 2019
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We study quantum transport after an inhomogeneous quantum quench in a free
fermion lattice system in the presence of a localised defect. Using a new
rigorous analytical approach for the calculation of large time and distance
asymptotics of physical observables, we derive the exact profiles of particle
density and current. Our analysis shows that the predictions of a semiclassical
approach that has been extensively applied in similar problems match exactly
with the correct asymptotics, except for possible finite distance corrections
close to the defect. We generalise our formulas to an arbitrary non-interacting
particle-conserving defect, expressing them in terms of its scattering
properties.
Dr Sotiriadis: "We would like to thank the ref..."
in Submissions | report on Non-equilibrium quantum transport in presence of a defect: the non-interacting case