Cavity-enhanced two-photon source emitting narrow linewidth telecommunication wavelength photons for improved quantum memory-coupling efficiency enabling long-distance quantum communications

Abstract

In long-distance quantum communication using quantum repeaters with quantum memories, entangled photons at telecommunication wavelengths that can be coupled to quantum memory with high efficiency are required. Typically, entangled photons are generated via spontaneous parametric down conversion (SPDC). However, the phase-matching bandwidth of SPDC is more than 100 GHz, which is much broader than the bandwidth of a Pr3+:Y2SiO5 quantum memory (with overall bandwidth of ∼10 GHz while the bandwidth of each frequency channel is ∼10 MHz) suitable for frequency-multiplexed quantum repeaters. In this study, nondegenerate SPDC (1550 nm and 995 nm) inside an optical cavity is used to obtain a narrow linewidth and cluster width of SPDC to match the Pr3+:Y2SiO5 bandwidth. We also developed a cavity control mechanism that can fulfill the doubly resonant condition. The developed two-photon source can maximize the coupling efficiency with Pr3+:Y2SiO5 by introducing wavelength conversion and is promising for use in a quantum repeater.