Spectrally indistinguishable biphotons via dual spontaneous four-wave mixing processes

We model the generation of multiple photon pairs (biphotons) through engineering of two coexisting nearly resonant spontaneous four-wave-mixing (SFWM) processes in five-level atoms driven to a quasi-dark state trapping regime. This is achieved through a suitable choice of two pump beams and one coupling beam whose spectral profiles are taken into account both to provide realistic estimates for the effects of their linewidths on atomic populations, coherences, and photon correlations and to engineer the joint spectral amplitude (JSA) distributions of generated biphotons directly by tuning the beams' parameters. We specifically leverage this tunability to control the degree of spectral indistinguishability of two biphotons with ultranarrow linewidths. The large degree of indistinguishability achievable in our model can be harnessed for advanced applications in quantum communication and information processing and potentially adapted to compatible solid-state interfaces.