Spyros Sotiriadis

Quantum quench from a thermal initial state

We consider a quantum quench in a system of free bosons, starting from a thermal initial state. As in the case where the system is initially in the ground state, any finite subsystem eventually reaches a stationary thermal state with a momentum-dependent effective temperature. We find that this can, in some cases, even be lower than the initial temperature. We also study lattice effects and discuss more general types of quenches.

Validity of the GGE for quantum quenches from interacting to noninteracting models

In the majority of the analytical verifications of the conjecture that the Generalised Gibbs Ensemble describes the large time asymptotics of local observables in quantum quench problems, both the postquench and the pre-quench Hamiltonians are essentially noninteracting. We test this conjecture studying the field correlations in the more general case of an arbitrary pre-quench Hamiltonian, while keeping the post-quench one noninteracting. We first show that in the previously studied special case of a noninteracting pre-quench Hamiltonian, the validity of the conjecture is a consequence of Wicks theorem. We then show that it is also valid in the general case of an arbitrary interacting pre-quench Hamiltonian, but this time as a consequence of the cluster decomposition property of the initial state, which is a fundamental principle for generic physical states. For arbitrary initial states that do not satisfy the cluster decomposition property, the above conjecture is not generally true. As a byproduct of our investigation we obtain an analytical derivation of earlier numerical results for the large time evolution of correlations after a quantum quench of the interaction in the Lieb-Liniger model from a nonzero value to zero.

Inhomogeneous quantum quenches

We study the problem of a quantum quench in which the initial state is the ground state of an inhomogeneous Hamiltonian, in two different models, conformal field theory and ordinary free field theory, which are known to exhibit thermalization of finite regions in the homogeneous case. We derive general expressions for the evolution of the energy flow and correlation functions, as well as the entanglement entropy in the conformal case. Comparison of the results from the two approaches in the regime of their common validity shows agreement up to a point further discussed. Unlike for the thermal analogue, the evolution in our problem is non-diffusive and can be physically interpreted using an intuitive picture of quasiparticles emitted from the initial time hypersurface and propagating semiclassically.

Equilibration of a Tonks-Girardeau gas following a trap release.

We study the nonequilibrium dynamics of a Tonks-Girardeau gas released from a parabolic trap to a circle. We present the exact analytic solution of the many body dynamics and prove that, for large times and in a properly defined thermodynamic limit, the reduced density matrix of any finite subsystem converges to a generalized Gibbs ensemble. The equilibration mechanism is expected to be the same for all one-dimensional systems.

Quantum quench in interacting field theory: A self-consistent approximation

We study a composite quantum quench of the energy gap and the interactions in the interacting

Quench dynamics of a Tonks–Girardeau gas released from a harmonic trap

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Memory-preserving equilibration after a quantum quench in a one-dimensional critical model

model using a self-consistent approximation. First we review results for free theories where a quantum quench of the energy gap or mass leads for long times to stationary behavior with thermal characteristics. An exception to this rule is the

Boundary state in an integrable quantum field theory out of equilibrium

2d

Initial states in integrable quantum field theory quenches from an integral equation hierarchy

case with zero mass after the quench. In the composite quench, however, we find that the effect of the interactions in our approximation is simply to effectively change the value of the mass. This means on the one hand that the interacting model also exhibits the same stationary behavior and on the other hand that this is now true even for the massless

Equilibration and GGE in interacting-to-free quantum quenches in dimensions

2d