41 research outputs found
Time-Dependent Mean Field Theory for Quench Dynamics in correlated electron systems
A simple and very flexible variational approach to the out-of-equilibrium
quantum dynamics in strongly correlated electron systems is introduced through
a time-dependent Gutzwiller wavefunction. As an application, we study the
simple case of a sudden change of the interaction in the fermionic Hubbard
model and find at the mean field level an extremely rich behaviour. In
particular, a dynamical transition between small and large quantum quench
regimes is found to occur at half-filling, in accordance with the analysis of
Eckstein {\sl et al.}, Phys. Rev. Lett. {\bf 103}, 056403 (2009), obtained by
dynamical mean field theory, that turns into a crossover at any finite doping.Comment: 4 pages, 2 figures, published versio
Transient Orthogonality Catastrophe in a Time Dependent Nonequilibrium Environment
We study the response of a highly-excited time dependent quantum many-body
state to a sudden local perturbation, a sort of orthogonality catastrophe
problem in a transient non-equilibrium environment. To this extent we consider,
as key quantity, the overlap between time dependent wave-functions, that we
write in terms of a novel two-time correlator generalizing the standard
Loschmidt Echo. We discuss its physical meaning, general properties, and its
connection with experimentally measurable quantities probed through
non-equilibrium Ramsey interferometry schemes. Then we present explicit
calculations for a one dimensional interacting Fermi system brought out of
equilibrium by a sudden change of the interaction, and perturbed by the
switching on of a local static potential. We show that different scattering
processes give rise to remarkably different behaviors at long times, quite
opposite from the equilibrium situation. In particular, while the forward
scattering contribution retains its power law structure even in the presence of
a large non-equilibrium perturbation, with an exponent that is strongly
affected by the transient nature of the bath, the backscattering term is a
source of non-linearity which generates an exponential decay in time of the
Loschmidt Echo, reminiscent of an effective thermal behavior.Comment: v3: minor changes, published versio
Multistability of Driven-Dissipative Quantum Spins
We study the dynamics of lattice models of quantum spins one-half, driven by
a coherent drive and subject to dissipation. Generically the meanfield limit of
these models manifests multistable parameter regions of coexisting steady
states with different magnetizations. We introduce an efficient scheme
accounting for the corrections to meanfield by correlations at leading order,
and benchmark this scheme using high-precision numerics based on
matrix-product-operators in one- and two-dimensional lattices. Correlations are
shown to wash the meanfield bistability in dimension one, leading to a unique
steady state. In dimension two and higher, we find that multistability is again
possible, provided the thermodynamic limit of an infinitely large lattice is
taken first with respect to the long time limit. Variation of the system
parameters results in jumps between the different steady states, each showing a
critical slowing down in the convergence of perturbations towards the steady
state. Experiments with trapped ions can realize the model and possibly answer
open questions in the nonequilibrium many-body dynamics of these quantum
systems, beyond the system sizes accessible to present numerics
Emergent Finite Frequency Criticality of Driven-Dissipative Correlated Lattice Bosons
Critical points and phase transitions are characterized by diverging
susceptibilities, reflecting the tendency of the system toward spontaneous
symmetry breaking. Equilibrium statistical mechanics bounds these instabilities
to occur at zero frequency, giving rise to static order parameters. In this
work we introduce a new class of dynamical transitions in a quantum many body
system far from thermal equilibrium, characterized by a susceptibility
diverging at a finite non-zero frequency, an emerging scale set by interactions
and non-equilibrium effects. In the broken-symmetry phase the corresponding
macroscopic order parameter becomes non-stationary and oscillates in time
without damping, thus breaking continuous time-translational symmetry. Our
results, obtained for a paradigmatic model of bosons interacting on lattice in
prensence of drive and dissipation, are relevant for the upcoming generation of
circuit QED arrays experiments and outline a generic framework to study
time-domain instabilities in non-equilibrium quantum systems, including Floquet
time crystals and quantum synchronization.Comment: 10 pages, 8 figure
Enhancement of Local Pairing Correlations in Periodically Driven Mott Insulators
We investigate a model for a Mott insulator in presence of a time-periodic
modulated interaction and a coupling to a thermal reservoir. The combination of
drive and dissipation leads to non-equilibrium steady states with a large
number of doublon excitations, well above the maximum thermal-equilibrium
value. We interpret this effect as an enhancement of local pairing
correlations, providing analytical arguments based on a Floquet Hamiltonian.
Remarkably, this Hamiltonian shows a tendency to develop long-range staggered
superconducting correlations. This suggests the possibility of realizing the
elusive eta-pairing phase in driven-dissipative Mott Insulators.Comment: 6+5 page
Correlation-induced steady states and limit cycles in driven dissipative quantum systems
We study a driven-dissipative model of spins one-half (qubits) on a lattice
with nearest-neighbor interactions. Focusing on the role of spatially extended
spin-spin correlations in determining the phases of the system, we characterize
the spatial structure of the correlations in the steady state, as well as their
temporal dynamics. In dimension one we use essentially exact
matrix-product-operator simulations on large systems, and pushing these
calculations to dimension two, we obtain accurate results on small cylinders.
We also employ an approximation scheme based on solving the dynamics of the
mean field dressed by the feedback of quantum fluctuations at leading order.
This approach allows us to study the effect of correlations in large lattices
with over one hundred thousand spins, as the spatial dimension is increased up
to five. In dimension two and higher we find two new states that are stabilized
by quantum correlations and do not exist in the mean-field limit of the model.
One of these is a steady state with mean magnetization values that lie between
the two bistable mean-field values, and whose correlation functions have
properties reminiscent of both. The correlation length of the new phase
diverges at a critical point, beyond which we find emerging a new limit cycle
state with the magnetization and correlators oscillating periodically in time.Comment: 21 pages, 25 figures. v2 includes some clarification
Real-Time Diagrammatic Monte Carlo for Nonequilibrium Quantum Transport
We propose a novel approach to nonequilibrium real-time dynamics of quantum
impurities models coupled to biased non-interacting leads, such as those
relevant to quantum transport in nanoscale molecular devices. The method is
based on a Diagrammatic Monte Carlo sampling of the real-time perturbation
theory along the Keldysh contour. We benchmark the method on a non-interacting
resonant level model and, as a first non-trivial application, we study zero
temperature non-equilibrium transport through a vibrating molecule.Comment: 5 pages, 3 figure
Enhanced entanglement negativity in boundary-driven monitored fermionic chains
We investigate entanglement dynamics in continuously monitored open quantum systems featuring current-carrying nonequilibrium states. We focus on a prototypical one-dimensional model of boundary-driven noninteracting fermions with monitoring of the local density, whose average Lindblad dynamics features a well-studied ballistic to diffusive crossover in transport. Here we analyze the dynamics of the fermionic negativity, mutual information, and purity along different quantum trajectories. We show that monitoring this boundary-driven system enhances its entanglement negativity at long times, which otherwise decays to zero in the absence of measurements. This result is in contrast with the case of unitary evolution where monitoring suppresses entanglement production. For small values of gamma, the stationary-state negativity shows a logarithmic scaling with system size, transitioning to an area-law scaling as gamma is increased beyond a critical value. Similar critical behavior is found in the mutual information, while the late-time purity shows no apparent signature of a transition, being O(1) for all values of gamma. Our work unveils the double role of weak monitoring in current-driven open quantum systems, simultaneously damping transport and enhancing entanglement