Quantum chaos and critical behavior on a chip

TL;DR

This paper explores the critical and chaotic behavior of an open-system Dicke model with a transport qubit, demonstrating how phase transitions and chaos can be observed and affected in circuit QED setups.

Contribution

It extends the open-system Dicke model to include a transport qubit, analyzing its impact on phase transition scaling and quantum chaos in a realistic circuit QED environment.

Findings

Superradiant phase transition scaling observed via transport measurements

Chaotic behavior persists in open-system conditions

Back-action and losses influence the phase transition dynamics

Abstract

The Dicke model describes N qubits (or two-level atoms) homogenously coupled to a bosonic mode. Here we examine an open-system realization of the Dicke model, which contains critical and chaotic behaviour. In particular, we extend this model to include an additional open transport qubit (TQ) (coupled to the bosonic mode) for passive and active measurements. We illustrate how the scaling (in the number of qubits N) of the superradiant phase transition can be observed in both current and current-noise measurements through the transport qubit. Using a master equation, we also investigate how the phase transition is affected by the back-action from the transport qubit and losses in the cavity. In addition, we show that the non-integrable quantum chaotic character of the Dicke model is retained in an open-system environment. We propose how all of these effects could been seen in a circuit QED system formed from an array of superconducting qubits, or an atom chip, coupled to a quantized resonant cavity (e.g., a microwave transmission line).