Microtoroid cavity QED with fiber overcoupling and strong atom-field coupling: a single-atom quantum switch for coherent light fields

TL;DR

This paper presents a scheme for single-atom quantum control of light propagation in a microtoroid resonator system, enabling high-fidelity entangled state preparation with strong atom-field coupling and overcoupling techniques.

Contribution

It introduces a novel scheme for atom-controlled light directionality in microtoroid resonators operating beyond the bad-cavity regime, with potential for high-fidelity quantum state engineering.

Findings

High-fidelity entangled atom-photon states are achievable with realistic parameters.

The scheme operates effectively with stronger incident fields while maintaining coherence.

Overcoupling and strong atom-field coupling are key to the scheme's success.

Abstract

We propose a scheme for single-atom, quantum control of the direction of propagation of a coherent field incident, via a tapered fiber, upon a microtoroidal whispering-gallery-mode (WGM) resonator. The scheme involves overcoupling of the fiber-taper to the resonator and strong coupling of an atom to the evanescent field of the WGM, i.e., an atom-field coupling that exceeds the total WGM linewidth. In contrast to previous, related schemes that operate in the bad-cavity regime, the proposed scheme can operate effectively with much stronger incident fields, while also preserving their coherent nature. It can also serve to prepare an entangled state of the atom and coherent optical pulses propagating in opposite directions along the fiber. We evaluate the fidelity of preparation of such a state taking into account absorption and atomic spontaneous emission and demonstrate that high fidelities should be possible with realistic parameters.