Intensity Interferometry revival on the C\^ote d'Azur

TL;DR

Recent technological advances have revitalized intensity interferometry for astronomy, offering potential advantages over amplitude interferometry, especially for very long baselines and shorter wavelengths, demonstrated by a prototype at Calern Observatory.

Contribution

The paper reports the development of a sensitive intensity interferometry prototype that significantly improves upon historical measurements and discusses future implementation possibilities.

Findings

Achieved a 100-fold sensitivity gain over original Hanbury Brown and Twiss setup.

Successfully measured temporal and spatial correlations in astronomical signals.

Proposed integration of the technique with existing large-scale observatories.

Abstract

Recent advances in photonics have revived the interest in intensity interferometry for astronomical applications. The success of amplitude interferometry in the early 1970s, which is now mature and producing spectacular astrophysical results (e.g. GRAVITY, MATISSE, CHARA, etc.), coupled with the limited sensitivity of intensity interferometry stalled any progress on this technique for the past 50 years. However, the precise control of the optical path difference in amplitude interferometry is constraining for very long baselines and at shorter wavelengths. Polarization measurements are also challenging in amplitude interferometry due to instrumental effects. The fortuitous presence of strong groups in astronomical interferometry and quantum optics at Universite Cote d'Azur led to the development of a prototype experiment at Calern Observatory, allowing the measure of the temporal correlation g(2)(\tau, r=0) in 2016 and of the spatial correlation g^(2)(r) in 2017 with a gain in sensitivity (normalized in observing time and collecting area) of a factor ~100 compared to Hanbury Brown and Twiss's original Narrabri Interferometer. We present possible ways to further develop this technique and point to possible implementations on existing facilities, such as CTA, the VLTI ATs or the summit of Maunakea, which offer a unique scientific niche.