Quantum storage of frequency-multiplexed photons exhibiting nonclassical correlations with telecom C-band photons

Abstract

Multiplexing is essential for improving entanglement distribution rates in quantum communication. Frequency multiplexing provides a promising and scalable path toward large-capacity quantum networks. Further progress requires increasing the number of frequency modes and developing broadband photon-pair sources and quantum memories that are spectrally compatible. Here, we report the integration of a cavity-enhanced spontaneous parametric downconversion source in the telecom C-band with a frequency-multiplexed atomic frequency-comb memory. The bow-tie cavity source was simultaneously resonant at 606 and 1550 nm, generating non-degenerate photon pairs exhibiting a clustered frequency-comb spectrum. The atomic frequency-comb memory, implemented in a Praseodymium-doped Yttrium Orthosilicate crystal, provided up to 83 frequency modes with 123 MHz spacing and enabled broadband storage of 606 nm signal photons. By filtering the main cluster, we obtained 32.7±4.8 effective modes, as confirmed from coincidence measurements. Importantly, we observed strong nonclassical correlations after storage, with cross correlation values of gs,i(2)=8.1±0.7. Our experimental results demonstrate the feasibility of integrating cavity-enhanced photon-pair sources with rare-earth-ion-doped solid-state memories. The integration reveals a high frequency multiplicity that is essential for scalable quantum networks.