Quantum quenches, linear response and superfluidity out of equilibrium
by
Davide Rossini(Scuola Normale Superiore, Pisa)
→
Europe/Rome
248 (Building C, First Floor)
248
Building C, First Floor
Description
Triggered by the impressive progress in the experimental study of ultracold atomic gases, where both the initial state and the Hamiltonian dynamics can be engineered with unprecedented accuracy, last years have witnessed a burst in the theoretical understanding of the equilibration of closed systems. While so far the behavior of the expectation value of observables in the stationary state has been mainly addressed, we know that the response to external (static or dynamic) perturbations can be equally important to characterize the properties of a quantum system.
We propose a characterization of stationary states at long times after a sudden quench in terms of time averaged response functions, and use these ideas to describe non-thermal steady states attained by low dimensional superfluids.
In particular, we analyze the sensitivity, quantified by the helicity modulus and the stiffness, of the long-time stationary state of a many-body quantum system to an infinitesimal twist at the boundary conditions. We apply our theory to two paradigmatic examples of hard-core bosons in a one-dimensional ring, quenched to/from superfluid/insulating phases. We show that the out-of-equilibrium stiffness is qualitatively different from the equilibrium case.
