Ultra-Strong Coupling in Cavity Quantum Electrodynamics: From Single to Multiple Emitters

近年来，在实验中已经达到了量子发射极与空腔光子之间的耦合强度与光子能量或发射极跃迁能量相当的新空穴量子电动力学。在这种超强耦合机制中，人们期待着迄今为止尚未探索的光-物质相互作用的新效应。在这个项目中，我们将首先研究如何在这种情况下通过实验获取有关腔内物理的信息。对于这个实验上非常关键的方面，我们将开发出对腔内状态进行完整断层扫描的方法。为了探索超强耦合机制的丰富物理学，我们将研究电路量子电动力学中的合适设置，作为我们感兴趣的最先进的技术平台之一。特别是，我们将探索与单个或多个量子位进行超强耦合的大型谐振器或开放式传输线。对于单个量子比特，我们将研究光脉冲在量子比特上的散射及其作为自旋玻色子物理量子模拟器的能力。量子比特与开放传输线的超强耦合可以形成光子数和频率选择可切换镜，因此我们将详细探索这些应用。对于多个量子位，我们期望系统产生一个广义的超强耦合，多模Dicke模型，显示出新颖的物理特性。我们将彻底研究它的性质和动力学，包括可能的量子相变。

In recent years a new regime of cavity quantum electrodynamics, where the coupling strength between a quantum emitter and a cavity photon becomes comparable to the photon energy or the emitter transition energy, has been reached in experiments. In this regime of ultra-strong coupling novel, to date unexplored effects of light-matter interaction are expected. In this project we will first investigate how information about the intra-cavity physics can be experimentally accessed in that regime. For this experimentally very crucial aspect we will develop approaches to a full tomography of the intra-cavity states. To explore the rich physics of the ultra-strong coupling regime we will then investigate suitable setups in circuit quantum electrodynamics as one of the most advanced technological platforms for our interests. In particular we will explore large resonators or open transmission lines that couple ultra-strongly to a single or to multiple qubits. For a single qubit we will investigate the scattering of light pulses at the qubit and its capability to act as a quantum simulator for spin-boson physics. Qubits that couple ultra-strongly to an open transmission line could form photon number and frequency selective switchable mirrors and we will thus explore these applications in detail. For multiple qubits we expect the system to give rise to a generalized ultra-strong coupling, multimode Dicke model that shows novel physics. We will throughly investigate its properties and dynamics, including possible quantum phase transitions.