Collective far-from-equilibrium behavior in quantum gases: Open and Closed Systems

In this presentation, I will discuss non-equilibrium aspects of
Bosonic atoms in two different scenarios, (i) when it behaves as an
isolated quantum system out-of equilibrium and (ii) when it is an open
quantum system in which the Bose gas is driven and coupled to photons
inside a leaky cavity.

I will first discuss the nonlinear dynamics of an isolated Bose
gas. In particular, I will discuss the physics and universality
arising upon quenching an excited state corresponding to a collective
solitonic excitation. I will show that, in this case, the Bose gas
falls into the universality class described by the Korteweg-de Vries
equation [1]. I will also discuss results on dynamical critical
phenomenon of a 1D Bose gas and show its strong connection to the
Kardar-Parisi-Zhang universality class [2,3].

I will then discuss an open quantum system consisting of a Bose gas
placed in an optical cavity and pumped by a laser [4]. This can be
mapped to a non-local Gross-Pitaeveski equation and also to the
Caldeira-Leggett model of quantum dissipation. I will describe the
non-trivial dissipative properties near the critical point of an open
quantum phase transition [5], which explained recent surprising
experimental findings. I will also describe the rich dynamics of this
driven-dissipative quantum gas and show this to be deeply rooted in
the theory of non-Hermitian physics and the pseudo-spectrum of this
open quantum system [6].

(1) M. Kulkarni, A. G. Abanov, Phys. Rev. A, 86, 033614; F. Franchini,
A. Gromov , M. Kulkarni, A. Trombettoni, (2014) 
(2) M. Kulkarni, D. A. Huse, H. Spohn (2014); M. Kulkarni,
A. Lamacraft, Phys. R ev. A 88, 021603, Rapid Communication 
(3) M. Kulkarni, Journal of Statistical Physics  (invited article,
2014) 
(4) R. Mottl et al, Science 336, 1570 (2012); K. Baumann et al, Nature
464, 1301 (2010)
(5) M. Kulkarni, B. Oztop and H. E. Tureci, Phys. Rev. Lett, 111,
220408 
(6) M. Kulkarni, K. G. Makris, H. E. Tureci (2014)