Exploring Symmetry Breaking at the Dicke Quantum Phase Transition

Abstract

We study symmetry breaking at the Dicke quantum phase transition by coupling a motional degree of freedom of a Bose-Einstein condensate to the field of an optical cavity. Using an optical heterodyne detection scheme, we observe symmetry breaking in real time and distinguish the two superradiant phases. We explore the process of symmetry breaking in the presence of a small symmetry-breaking field and study its dependence on the rate at which the critical point is crossed. Coherent switching between the two ordered phases is demonstrated.

Signatures of quantum fluctuations in the Dicke model by means of Rényi uncertainty

“…To illustrate it we selected the Dicke model that proved to be very useful in studying quantum optical [34][35][36][37][38], chaotic [38,39] or entanglement [40] properties. It has been realized with a superfluid gas in an optical cavity [41] and the spontaneous symmetry breaking has been observed recently [42]. There is a QPT in the N → ∞ limit.…”

Creating a tunable spin squeezing via a time-dependent collective atom-photon coupling

“…Recently, a similar setup has been considered experimentally in a BEC-cavity system, and a remarkable quantum phase transition, from a normal phase to a superradiant phase of the Dicke model, was observed [31,32]. The distinct advantage of this setup is that the realized * chengang971@163.com † tjia@sxu.edu.cn ‡ fnori@riken.jp Dicke model has a tunable collective atom-photon coupling through manipulating the intensities of the classical driving lasers [33].…”

“…In the high-frequency approximation, we demonstrate explicitly that this spin squeezing arises from a strong repulsive spin-spin interaction induced by the time-dependent collective atom-photon coupling (for the undriven Dicke model, only a weak attractive spinspin interaction is generated). Finally, we evaluate analytically, using current experimental parameters [31,32], the MSF, which can reach 40 dB. This giant MSF is far larger than previous ones [12][13][14][15][16][17][18][19][20].…”

Nonlinear atom-photon-interaction-induced population inversion and inverted quantum phase transition of Bose-Einstein condensate in an optical cavity

“…A significant achievement is the experimental study of the quantum behaviors of Bose-Einstein condensates (BECs) in ultrahigh-finesse optical cavities [2,9]. More recently the time-dependent nonequilibrium experiments were performed in an open cavity [10,11], which lead to the theoretical interpretations of nonequilibrium QPT [12][13][14][15][16].…”