Single-photon sources based on optical parametric processes have been usedextensively for quantum information applications due to their flexibility,room-temperature operation and potential for photonic integration. However, theintrinsically probabilistic nature of these sources is a major limitation forrealizing large-scale quantum networks. Active feedforward switching of photonsfrom multiple probabilistic sources is a promising approach that can be used tobuild a deterministic source. However, previous implementations of thisapproach that utilize spatial and/or temporal multiplexing suffer from rapidlyincreasing switching losses when scaled to a large number of modes. Here, webreak this limitation via frequency multiplexing in which the switching lossesremain fixed irrespective of the number of modes. We use the third-ordernonlinear process of Bragg scattering four-wave mixing as an efficientultra-low noise frequency switch and demonstrate multiplexing of threefrequency modes. We achieve a record generation rate of $4.6\times10^4$multiplexed photons per second with an ultra-low $g^{2}(0)$ = 0.07, indicatinghigh single-photon purity. Our scalable, all-fiber multiplexing system has atotal loss of just 1.3 dB independent of the number of multiplexed modes, suchthat the 4.8 dB enhancement from multiplexing three frequency modes markedlyovercomes switching loss. Our approach offers a highly promising path tocreating a deterministic photon source that can be integrated on a chip-basedplatform.
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