Massively parallel Hong-Ou-Mandel interference based on independent soliton microcombs

Hong-Ou-Mandel (HOM) interference is the foundation of quantum optics to test the degree of indistinguishability of two incoming photons, playing a key role in quantum communication, sensing, and photonic quantum computing. Realizing high-visibility HOM interference with massively parallel optical channels is challenging due to the lack of available natural optical references for aligning independent arrayed laser pairs. Here, we demonstrate 50 parallel comb-teeth pairs of continuous-wave weak coherent photons HOM interference using two independently frequency post-aligned soliton microcombs (SMCs), achieving an average fringe visibility over 46%. The frequencies of all comb-teeth pairs are long-term aligned by developing two sets of fully frequency-stabilized SMCs with independent reference and adjusting free spectral range beyond 100 kilohertz through perturbations in soliton state. The verification experiment proves the feasibility of constructing massively quantum information channels by co-opting classical wavelength division multiplexing optical communications, which paves the way for practical large-scale quantum communication systems.