Continuous quantum light from a dark atom

TL;DR

This paper demonstrates a quantum nonlinear wave-mixing experiment where strong atom-cavity coupling creates entangled dark states, leading to continuous quantum light emission with antibunching, by suppressing excited-state populations through quantum interference.

Contribution

It introduces a novel mechanism using entangled dark states and quantum Zeno effects to generate continuous quantum light from a single atom-cavity system.

Findings

Entanglement suppresses excited-state population via quantum interference.

Dark states form a harmonic ladder enabling continuous photon emission.

Photon antibunching results from quantum Zeno blockade.

Abstract

Cycling processes are important in many areas of physics ranging from lasers to topological insulators, often offering surprising insights into dynamical and structural aspects of the respective system. Here we report on a quantum-nonlinear wave-mixing experiment where resonant lasers and an optical cavity define a closed cycle between several ground and excited states of a single atom. We show that, for strong atom-cavity coupling and steady-state driving, the entanglement between the atomic states and intracavity photon number suppresses the excited-state population via quantum interference, effectively reducing the cycle to the atomic ground states. The system dynamics then result from transitions within a harmonic ladder of entangled dark states, one for each cavity photon number, and a quantum Zeno blockade that generates antibunching in the photons emitted from the cavity. The reduced cycle suppresses unwanted optical pumping into atomic states outside the cycle, thereby enhancing the number of emitted photons.