Superradiant quantum phase transition in a circuit QED system: a revisit from a fully microscopic point of view

TL;DR

This paper revisits the superradiant quantum phase transition in circuit QED systems from a microscopic perspective, confirming its existence and identifying parameters that control the transition.

Contribution

It derives the Dicke model with correct charging terms from first principles, demonstrating the superradiant phase transition in superconducting circuit QED systems.

Findings

Superradiant quantum phase transition can occur in circuit QED systems.

The transition is controllable via circuit parameters like capacitance ratios.

The model is derived from a microscopic many-body approach based on BCS theory.

Abstract

In order to examine whether or not the quantum phase transition of Dicke type exists in realistic systems, we revisit the model setup of the superconducting circuit QED from a microscopic many-body perspective based on the BCS theory with pseudo-spin presentation. By deriving the Dicke model with the correct charging terms from the minimum coupling principle, it is shown that the circuit QED system can exhibit superradiant quantum phase transition in the limit N\rightarrow\infty. The critical point could be reached at easiness by adjusting the extra parameters, the ratio of Josephson capacitance C_{J} to gate capacitance C_{g}, as well as the conventional one, the ratio of Josephson energy E_{J} to charging energy E_{C}.