Hanbury Brown-Twiss interference with massively parallel spectral multiplexing for broadband light

TL;DR

This work demonstrates massively parallel, wavelength-resolved two-photon interference by measuring Hanbury Brown-Twiss correlations across 100 spectral channels using a fast, data-driven spectrometer built around the LinoSPAD2 SPAD array. The system achieves $40~\mathrm{pm}$ spectral and $40~\mathrm{ps}$ temporal resolution over a $10~\mathrm{nm}$ bandwidth, enabling spectro-temporal photon correlations without narrowband filtering and preserving photon flux. The key contributions are the first broadband, frequency-multiplexed HBT observation across 100 channels with a high-throughput detector, and a data-processing pipeline capable of extracting per-channel interference contrasts from massive datasets. The results offer a scalable route to high-dimensional quantum interference and have practical implications for astro-interferometry, quantum communication, and room-temperature photonic networks, potentially enabling large-scale entanglement swapping and quantum sensing with thousands of spectral channels.

Abstract

Two-photon interference is a fundamental resource for quantum technologies and optical quantum computing, underpinning precision measurements, scalable entanglement distribution, and the operation of photonic circuits and quantum network protocols. Here, we report the first demonstration of massively parallel, wavelength-resolved photon bunching, revealing Hanbury Brown-Twiss correlations across 100 independent spectral channels. These observations are enabled by a fast, data-driven single-photon spectrometer that achieves 40 pm spectral and 40 ps temporal resolution over a 10 nm bandwidth, providing simultaneous access to spectro-temporal photon correlations without the need for narrowband filtering. This approach preserves photon flux while enabling high-dimensional quantum interference measurements across a broad spectrum. Our results establish frequency-multiplexed two-photon interference as a scalable and throughput-efficient platform for quantum-enhanced photonic technologies, offering a practical route toward room-temperature architectures that overcome loss limitations and advance the scalability for a variety of applications.

Figures (6)

• Figure 1: Conceptual illustration of wavelength-resolved two-photon interference. Broadband thermal light is split into two beams and analyzed using a dual-arm spectrometer, producing time- and wavelength-resolved single-photon spectra for each path. A spectro-temporal correlation analysis is performed between spectral channels on both sides. When photons occupy the same spectral bin $(\lambda_i = \lambda_j)$, quantum bunching leads to an HBT peak --- an enhancement in coincidence counts at small time delays between the two photons. In contrast, mismatched spectral bins $(\lambda_i \neq \lambda_j)$ yield flat, uncorrelated distributions, as expected for distinguishable photons. This setup enables massively parallel observation of two-photon interference across a wide spectral range.
• Figure 2: Layout of dual spectrometer with two light sources: neon lamp and light-emitting diode (LED). For both sources, the light is polarized with a linear polarizer (LP) and filtered through a spectral bandpass filter (SBF) before entering a fiber port (FP), where it is coupled into a single-mode fiber. The source switch (SS) is essentially a fiber-to-fiber connecting sleeve, which allows for the selection of one of the two sources at a time. A 1-to-2 50:50 fiber-coupled beamsplitter (FBS) splits and sends the light into two arms of the spectrometer. One of the arms is delayed via an additional single-mode fiber (SMF). Both arms are connected to adjustable collimators (AC) that are used for focusing the beams of light. With the help of a mirror (M), the output beams are guided onto a ruled reflective diffraction grating (RRDG). The resulting spectrum is focused via an achromatic doublet (AD) onto the LinoSPAD2 sensor (LS2). Everything besides the two light sources and fiber-coupling components is located inside a light-tight enclosure. All fibers used in this setup are single-mode ones, including the beamsplitter.
• Figure 3: Two 10 nm wide spectra in the dual spectrometer. The light source is an LED light passing through a $(640\pm5)$ nm bandpass filter. Two neon lines, 638.3 and 640.2 nm, measured in the same conditions as the broadband light, are overlaid with the broadband spectra, providing precise calibration of the spectrometers. Several weaker lines are also visible.
• Figure 4: a--d) Time difference distributions in two spectral bins in the dual spectrometer, four combinations in total (pixels 51 and 218, 90 and 179, 50 and 219, 46 and 223), with examples of different contrast values for HBT peaks determined by the fit. e) Sum of all diagonal combinations where the two frequencies are expected to be equal. The peak contrast as determined by a fitting procedure is equal to $(2.0 \pm 0.1)$% and sigma 70 ps; f) HBT peak after filtering with $(656.40\pm0.05)$ nm narrow band filter.
• Figure 5: Summary 2D histogram of contrasts extracted by the fitter from histograms of coincidences for each pair of spectral bins. The 1D plots above and on the right show the two spectra in the dual spectrometer. The diagonal corresponding to the spectral bins matched in frequency clearly shows the non-zero contrasts of the observed HBT peaks. As the edges of the two spectra have very low photon rates, this translates to large statistical fluctuations near the 2D histogram edges. The color scale for contrast values was limited from $-1$% to 5% to remove a small number of outliers on the edges. Empty vertical and horizontal lines correspond to several noisy, and therefore masked pixels, and also to dead pixels.