Universal theory of multipartite cavity quantum electrodynamics

TL;DR

This paper develops a comprehensive, exact theoretical framework and numerical tools for analyzing multipartite cavity quantum electrodynamics systems, revealing new phenomena in ultrastrong coupling regimes and enabling simulation of spin-entanglement experiments.

Contribution

It introduces a full, approximation-free model and a high-precision numerical code for multipartite cavity QED, advancing understanding of ultrastrong coupling effects and spin entanglement.

Findings

Ultrastrong coupling leads to chaos and phase transitions in quantum systems.

The developed code accurately tracks system evolution with arbitrary initial conditions.

First numerical observation of chaos and phase changes in ultrastrong coupling regimes.

Abstract

Cavity quantum electrodynamics of multipartite systems is studied in depth, which consist of an arbitrary number of emitters in interaction with an arbitrary number of cavity modes. The governing model is obtained by taking the full field-dipole and dipole-dipole interactions into account, and is solved in the Schr\"odinger picture without assumption of any further approximation. An extensive code is developed which is able to accurately solve the system and track its evolution with high precision in time, while maintaining sufficient degrees of arbitrariness in setting up the initial conditions and interacting partitions. Using this code, we have been able to numerically evaluate various parameters such as probabilities, expectation values (of field and atomic operators), as well as the concurrence as the most rigorously defined measure of entanglement of quantum systems. We present and discuss several examples including a seven-partition system consisting of six quantum dots interacting with one cavity mode. We observe for the first time that the behavior of quantum systems under ultrastrong coupling is significantly different than the weakly and strongly coupled systems, marked by onset of a chaos and abrupt phase changes. We also discuss how to implement spin into the theoretical picture and thus successfully simulate a recently reported spin-entanglement experiment.