Quantum nonlinear cavity QED with coherently prepared atoms

TL;DR

This paper demonstrates the first direct observation of quantum nonlinearity in a multiatom cavity QED system by controlling multi-photon excitations through quantum interference, confirmed by experiments with cold Rb atoms.

Contribution

It introduces a method to observe multiphoton transitions in multiatom CQED systems via destructive interference, supported by experimental validation and quantum theoretical analysis.

Findings

Observation of three-photon excitation of CQED ladder states

Agreement with quantum, but not semiclassical, theoretical models

First experimental evidence of quantum nonlinearity in multiatom CQED

Abstract

We propose a method to study the quantum nonlinearity and observe the multiphoton transitions in a multiatom CQED system. We show that by inducing simultaneously destructive quantum interference for the single-photon and two-photon excitations in the CQED system, it is possible to observe the direct three-photon excitation of the higher-order ladder states of the CQED system. We report an experiment with cold Rb atoms confined in an optical cavity and demonstrate such interference control of the multi-photon excitations of the CQED system. The observed nonlinear excitation of the CQED ladder states agrees with a theoretical analysis based on a fully quantized treatment of the CQED system, but disagrees with the semiclassical analysis of the CQED system. Thus it represents the first direct observation of the quantum nature of the multiatom CQED system and opens new ways to explore quantum nonlinearity and its applications in quantum optical systems in which multiple absorbers/emitters are coupled with photons in confined cavity structures.