Photon-Counting Intensity Interferometry with Superconducting Nanowire Single-Photon Detectors

This thesis presents photon-counting intensity interferometry measurements of spectrally filtered thermal light (λ = 653 nm, Δλ ≈ 1 nm) using a zero-baseline Hanbury Brown–Twiss setup. Two single-photon detector technologies are compared: silicon avalanche photodiodes (APDs) and superconducting nanowire single-photon detectors (SNSPDs) fabricated at TU Delft. Five configurations are investigated, progressing from an APD pair through single-pixel SNSPDs to four-pixel SNSPD arrays with TTCombiner channel combining. Photon bunching is observed in all configurations. The APD pair yields a bunching contrast of C = 2.28 × 10⁻³ with a FWHM of 510 ps. Single-pixel SNSPD operation reduces the FWHM to 293 ps but reveals jitter degradation at high count rates. The four-pixel configuration recovers the intrinsic timing resolution, achieving a FWHM of 89 ps — 5.7× narrower than the APD peak — and a bunching contrast of 8.96 × 10⁻³, a 3.9× improvement driven by the relation C ∝ 1/FWHM. The results validate multi-pixel SNSPD arrays as a transformative technology for stellar intensity interferometry.