Light from an ion crystal: bunching or antibunching?

TL;DR

This study demonstrates a free-space light source from two trapped ions whose photon statistics can be tuned between bunching and antibunching by changing observation direction, revealing complex quantum light behavior.

Contribution

It shows that photon statistics from a two-ion system can be spatially controlled, exhibiting a crossover between bunching and antibunching, modeled with the Dicke entanglement framework.

Findings

Measured $g^{(2)}(0)$ varies from 0.60 to 1.46 depending on detector position.

Photon statistics depend on observation direction, demonstrating a continuous crossover.

Results align with Dicke model predictions of entangled states.

Abstract

Photon statistics divides light sources into three different categories, characterized by bunched, antibunched or uncorrelated photon arrival times. Single atoms, ions, molecules, or solid state emitters display antibunching of photons, while classical thermal sources exhibit photon bunching. Here we demonstrate a light source in free space, where the photon statistics depends on the direction of observation, undergoing a continuous crossover between photon bunching and antibunching. We employ two trapped ions, observe their fluorescence under continuous laser light excitation, and record the spatially resolved autocorrelation function $g^{(2)}(\tau)$ with a movable Hanbury Brown and Twiss detector. Varying the detector position we find a minimum value for antibunching, $g^{(2)}(0) = 0.60(5)$ and a maximum of $g^{(2)}(0)=1.46(8)$ for bunching, demonstrating that this source radiates fundamentally different types of light alike. The observed variation of the autocorrelation function is understood in the Dicke model of heralded entangled states and the observed maximum and minimum values are modeled, taking independently measured experimental parameters into account.