https://indico.in2p3.fr/event/40032/

Speakers: Andrei Nomerotski (Czech Technical University in Prague) Quantum technologies critically rely on the ability to detect and identify indistinguishable photons, as only such photons exhibit high-contrast quantum interference. We present a new approach to real-time photon indistinguishability detection based on ultrafast spectro-temporal imaging using pixelated detectors. The concept maps each detected photon onto a well-defined time–frequency (t,ω) mode corresponding to an individual pixel, which effectively acts as a selector of the quantum state, enabling direct identification of interfering photon pairs as well as higher-order correlations. The implemented system combines an optical spectrometer with a fast pixelated readout based on a SPAD linear array (LinoSPAD2), achieving ~40 ps timing and ~40 pm spectral resolution. We report the first demonstration of massively parallel, wavelength-resolved photon bunching in two-photon Hanbury Brown–Twiss interference measurements for broadband light, simultaneously across ~100 independent spectral channels - an improvement of more than an order of magnitude over previous results [1]. This performance approaches the Heisenberg–Gabor limit for joint time–frequency measurements, a regime not accessible with existing detector technologies. We further present ongoing efforts to enhance spectral resolution using an echelle spectrometer architecture, targeting the regime where each pixel corresponds to a single spectro-temporal mode, as well as discussing prospects for extending the concept to fast two-dimensional detector arrays at Heisenberg–Gabor limit, targeting timing resolutions of ~20 ps and spectral resolutions of ~5 pm. A key feature of this approach is the ability to perform indistinguishability analysis and extend it toward real-time processing, drastically reducing data volumes by selecting only relevant photon events. Importantly, the method naturally generalizes beyond two-photon interference to genuine multiphoton correlation measurements, including photon-number-resolved events within single pixels. This technology opens new opportunities across multiple domains, including wavelength-multiplexed quantum communication, long-baseline astronomical interferometry, and quantum imaging and sensing with enhanced background rejection in photon-starved conditions. [1] Hanbury Brown-Twiss interference with massively parallel spectral multiplexing for broadband light, S Kulkov et al, preprint arXiv:2509.05649 (2025). https://indico.in2p3.fr/event/40519/