Comment on "Superradiant phase transitions and the standard description of circuit QED".

Superradiant phase transitions and the standard description of circuit QED.

We investigate the equilibrium behavior of a superconducting circuit QED system containing a large number of artificial atoms. It is shown that the currently accepted standard description of circuit QED via an effective model fails in an important aspect: it predicts the possibility of a superradiant phase transition, even though a full microscopic treatment reveals that a no-go theorem for suc...

Quantum phases in circuit QED with a superconducting qubit array

Circuit QED on a chip has become a powerful platform for simulating complex many-body physics. In this report, we realize a Dicke-Ising model with an antiferromagnetic nearest-neighbor spin-spin interaction in circuit QED with a superconducting qubit array. We show that this system exhibits a competition between the collective spin-photon interaction and the antiferromagnetic nearest-neighbor s...

A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements

First-order superradiant phase transitions in a multiqubit cavity system.

We predict the existence of novel first-order phase transitions in a general class of multiqubit cavity systems. Apart from atomic systems, the associated superradiant phase transition should be observable in a variety of solid-state experimental systems, including the technologically important case of interacting quantum dots coupled to an optical cavity mode.

Depolarization shift of the superradiant phase transition

Quantum electrodynamics, when applied to a large ensemble of identical atoms, leads to the surprising prediction that a so-called superradiant phase transition takes place above a critical density of the atom gas. In thermal equilibrium and also in the ground state of the system at zero temperature, the atoms in the superradiant phase develop a polarization field with non-vanishing mean value a...