M. J. Bhaseen

Holographic superfluids and the dynamics of symmetry breaking.

We explore the far-from-equilibrium response of a holographic superfluid using the AdS/CFT correspondence. We establish the dynamical phase diagram corresponding to quantum quenches of the order parameter source field. We find three distinct regimes of behavior that are related to the spectrum of black hole quasinormal modes. These correspond to damped oscillations of the order parameter and to overdamped approaches to the superfluid and normal states. The presence of three regimes, which includes an emergent dynamical temperature scale, is argued to occur more generally in time-reversal-invariant systems that display continuous symmetry breaking.

Collective Dynamics of Bose-Einstein Condensates in Optical Cavities

Experiments on Bose-Einstein condensates in optical cavities have observed a coherent state of the matter-light system-superradiance. The nature of these experiments demands consideration of collective dynamics. Including cavity leakage and the backreaction of the cavity field on the condensate, we find a rich phase diagram including multiphase coexistence regions, and persistent optomechanical oscillations. The proximity of the phase boundaries results in a critical slowing down of the decay of many-body oscillations, which can be enhanced by large cavity loss.

Towards a field theory of the plateau transitions in the integer quantum Hall effect

Abstract We suggest a procedure for calculating correlation functions of the local densities of states (DOS) at the plateau transitions in the integer quantum Hall effect (IQHE). We argue that their correlation functions are appropriately described in terms of the SL( 2, C )/SU(2) WZNW model (at the usual Kac–Moody point and with the level 6≤ k ≤8 ). In this model we have identified the operators corresponding to the local DOS, and derived the partial differential equation determining their correlation functions. The OPEs for powers of the local DOS obtained from this equation are in agreement with available results.

Dynamics of nonequilibrium Dicke models

Motivated by experiments observing self-organization of cold atoms in optical cavities, we investigate the collective dynamics of the associated nonequilibrium Dicke model. The model displays a rich semiclassical phase diagram of long-time attractors including distinct superradiant fixed points, bistable and multistable coexistence phases, and regimes of persistent oscillations. We explore the intrinsic time scales for reaching these asymptotic states and discuss the implications for finite-duration experiments. On the basis of a semiclassical analysis of the effective Dicke model, we find that sweep measurements over 200 ms may be required in order to access the asymptotic regime. We briefly comment on the corrections that may arise due to quantum fluctuations and states outside of the effective two-level Dicke model description.

Disordered Dirac fermions: the marriage of three different approaches

Abstract We compare the critical multipoint correlation functions for two-dimensional (massless) Dirac fermions in the presence of a random su ( N ) (non-Abelian) gauge potential, obtained by three different methods. We critically reexamine previous results obtained using the replica approach and in the limit of infinite disorder strength and compare them to new results (presented here) obtained using the supersymmetric approach to the N =2 case. We demonstrate that this menage a trois of different approaches leads to identical results. Remarkable relations between apparently different conformal field theories (CFTs) are thereby obtained. We further establish a connection between the random Dirac fermion problem and the c =−2 theory of dense polymers. The presence of the c =−2 theory may be seen in all three different treatments of the disorder.

Non-equilibrium steady states in the Klein–Gordon theory

We construct non-equilibrium steady states in the Klein-Gordon theory in arbitrary space dimension

Far from equilibrium energy flow in quantum critical systems

d

Quantum Quenches in Chern Insulators.

following a local quench. We consider the approach where two independently thermalized semi-infinite systems, with temperatures

Fermionic superradiance in a transversely pumped optical cavity

T_{\rm L}

Legendre's relation and the quantum equivalence osp(4|4)(1) = osp(2|2)(-2) + su(2)(0)

and