## "Fate of Orthogonality Catastrophe in driven-open quantum systems"

**Speaker:**Federico Tonielli, University of Cologne, Germany

**When:**May 11, 2018 (Fri), 12:00PM to 01:00PM (add to my calendar)

**Location:**SCI 352

**Hosted by:**Anatoli Polkovnikov

*This event is part of the Condensed Matter Theory Seminar Series. *

Orthogonality Catastrophe is a paragon of the dramatic effects provoked by the interaction of a gapless quantum many body system with an impurity. Its instance in real time dynamics is a universal, algebraic decay of the fidelity between the unperturbed ground state and the ground state evolved in the presence of the impurity itself.

We consider the case of a quantum system subject to a local dephasing channel, i.e. locally interacting with an external Markovian bath, that plays the role of a new type of impurity and whose dynamics is well described by a local Lindblad quantum master equation. We find in this new context, a novel, universal, time-resolved scaling behavior of the fidelity, that counteracts the exponential decay due to heating, unlike the case of unitary dynamics.

The first model we consider is the one-dimensional quantum Ising chain in transverse field with spin dephasing, where we establish this novel character for the fidelity by means of a resummation of the perturbative expansion.

We further investigate the phenomenon in a quantum field theory of free bosons subject to a stochastic impurity potential, localized in space but random in time, constructing a functional integral expression for the fidelity. The latter is computed for linear and quadratic impurity potentials, and for impurities with short correlations in time. An intriguing crossover to the familiar OC is found in the limit of infinite correlation time of the impurity, for which a physical picture is proposed. Finally, we ague how to detect the phenomenon through direct measurement of an accessible observable in cold atoms experiments.