Dissipation and Ultrastrong Coupling in Circuit QED

TL;DR

This paper investigates the effects of dissipation and ultrastrong coupling in circuit QED, revealing limitations of standard models and proposing a more accurate master equation that captures complex phenomena like sideband transitions and photon generation.

Contribution

It introduces a new master equation accounting for qubit-resonator coupling and dissipation, especially relevant in the ultrastrong coupling regime, improving upon standard quantum optics models.

Findings

Standard quantum optics master equation fails in ultrastrong coupling.

Asymmetry in vacuum Rabi splitting can probe dephasing noise.

Fluctuations induce sideband transitions, squeezing, and Casimir-like photons.

Abstract

Cavity and circuit QED study light-matter interaction at its most fundamental level. Yet, this interaction is most often neglected when considering the coupling of this system with an environment. In this paper, we show how this simplification, which leads to the standard quantum optics master equation, is at the root of unphysical effects. Including qubit relaxation and dephasing, and cavity relaxation, we derive a master equation that takes into account the qubit-resonator coupling. Special attention is given to the ultrastrong coupling regime, where the failure of the quantum optical master equation is manifest. In this situation, our model predicts an asymmetry in the vacuum Rabi splitting that could be used to probe dephasing noise at unexplored frequencies. We also show how fluctuations in the qubit frequency can cause sideband transitions, squeezing, and Casimir-like photon generation.