Exotic Quantum States of Circuit Quantum Electrodynamics in the Ultra‐Strong Coupling Regime

Abstract

The quantum coherent behaviors of superconducting devices at macroscopic scales and recent technical advances in fine tunability have brought the conventional cavity quantum electrodynamics (QED) to superconducting circuits. With an ultra-strong cavity photon-artificial atom coupling and the inherent nonlinearity of the Josephson junctions, the so-called circuit QED offers new opportunities to explore new realms of physics that have remained a challenge for conventional cavity QED. Circuit QED has even attracted public attention as the leading architecture for quantum computation. In this article, a pedagogical review of recent studies and activities on exotic quantum states that can be attributed to ultra-strong coupling is provided. A progress report on attempts to seek the smallest unit of the topological matter and its fundamental interaction with light is also provided.

Symmetry operators of the asymmetric two-photon quantum Rabi model

“…The quantum Rabi model (QRM) [1] which describes the simplest interaction between a twolevel system (qubit) and a single-mode cavity is a paradigmatic model in the quantum optics [2]. In the past decades, fascinating and inspiring research has proved on the QRM and other related generalized models, which has been highlighted in [3][4][5][6]. Besides, the exact solution of the QRM, which was firstly found by Braak in the Bargmann space representation [7] and later by Chen et al [8] in a more familiar Hilbert space using Bogoliubov operator approach (BOA), further promotes the developments in the models.…”

Double degeneracy associated with hidden symmetries in the asymmetric two-photon Rabi model

“…These studies have stimulated extensive interests in various QRMs [19][20][21][22][23][24][25][26][27]. For more theoretical details in this field, one may refer to recent review articles [28][29][30].…”

The hidden symmetry of the asymmetric two-photon Rabi model

“…It was soon realized that the Gfunction can be constructed in terms of the mathematically well-defined Heun confluent function [1]. For more theoretical details in this field, one may refer to recent review articles [27][28][29].…”