Temporal intensity interferometry: photon bunching on stars

А. А. Малыгин, Alexander N. Penin, Alexander V. Sergienko

Pierre Riaud

P. K. Tan, G. H. Yeo, H. S. Poh +2 more

Light from thermal blackbody radiators such as stars exhibits photon bunching behavior at sufficiently short timescales. However, with available detector bandwidths, this bunching signal is difficult to observe directly. We present an experimental technique to increase the photon bunching signal in blackbody radiation via spectral filtering of the light source. Our measurements reveal strong temporal photon bunching from blackbody radiation, including the Sun. This technique allows for an absolute measurement of the photon bunching signature g (2) (0), and thereby a direct statement on the statistical nature of a light source. Such filtering techniques may help revive the interest in intensity interferometry as a tool in astronomy.

Peng Kian Tan

Working in experimental quantum optics with focus on instrumentation for temporal intensity interferometry. Have successfully measured and resolved the temporal photon bunching effect from Sunlight in Singapore despite the tropical, humid, and urban environment. Our lab measurements have successfully identified the presence of coherent laser light even when embedded in a blackbody radiation background. Measurements also differentiated coherent laser light from thermal light that are both narrowband emission lines which could otherwise be mis-identified.

Filip Sośnicki, Michał Mikołajczyk, Sanjay Kapoor +3 more

Photons emitted by incoherent sources exhibit temporal bunching, a fundamental manifestation of Bose-Einstein statistics first observed by Hanbury Brown and Twiss (HBT). While intensity correlation measurements originated in astronomy and are now central across quantum technologies, biophysics, and spectroscopy, observing temporal bunching in broadband thermal light remains limited by detector temporal resolution. Conventional approaches - such as streak cameras or optical upconversion - introduce severe trade-offs in efficiency, bandwidth, or setup versatility. Here, we propose and demonstrate a third route: pre-detection temporal magnification of the optical field prior to measuring its intensity autocorrelation function in a conventional HBT setup. Using an electro-optic time lens with a temporal magnification of 660, we resolve the temporal intensity autocorrelation of broadband thermal light generated via non-degenerate spontaneous parametric down-conversion with a bandwidth of 250 GHz. This enables direct observation of thermal photon bunching on sub-3.5 picosecond timescales without narrow spectral filtering, establishing pre-detection temporal imaging as a general platform for broadband statistical optics, with applications spanning ultrafast quantum optics, biophysical imaging, and potentially stellar intensity interferometry.