Temporal intensity interferometry: photon bunching on three bright stars

TL;DR

This study demonstrates the first intensity correlation measurements of star light since Hanbury Brown and Twiss, confirming photon bunching in bright stars and opening pathways for long-baseline optical interferometry.

Contribution

It presents the first real-time photon bunching measurements on three bright stars using a 1m telescope, validating the technique for future long-baseline optical interferometry.

Findings

Photon bunching observed with contrast around 2×10⁻³

Results agree with theoretical expectations for chaotic sources

Method demonstrates feasibility for optical interferometry over large baselines

Abstract

We report the first intensity correlation measured with star light since Hanbury Brown and Twiss' historical experiments. The photon bunching $g^{(2)}(\tau, r=0)$, obtained in the photon counting regime, was measured for 3 bright stars, $\alpha$ Boo, $\alpha$ CMi, and $\beta$ Gem. The light was collected at the focal plane of a 1~m optical telescope, was transported by a multi-mode optical fiber, split into two avalanche photodiodes and digitally correlated in real-time. For total exposure times of a few hours, we obtained contrast values around $2\times10^{-3}$, in agreement with the expectation for chaotic sources, given the optical and electronic bandwidths of our setup. Comparing our results with the measurement of Hanbury Brown et al. on $\alpha$ CMi, we argue for the timely opportunity to extend our experiments to measuring the spatial correlation function over existing and/or foreseen arrays of optical telescopes diluted over several kilometers. This would enable $\mu$as long-baseline interferometry in the optical, especially in the visible wavelengths with a limiting magnitude of 10.