Degenerate photons from a cryogenic spontaneous parametric down-conversion source

We demonstrate the generation of degenerate photon pairs from spontaneous parametric down-conversion in titanium-indiffused waveguides in lithium niobate at cryogenic temperatures. Since the phase matching cannot be temperature tuned inside a cryostat, we rely on a precise empirical model of the refractive indices when fabricating a fixed poling period. We design the phase-matching properties of our periodic poling to enable signal and idler photons at 1559.3(6) nm and characterize the indistinguishability of our photons by performing a Hong-Ou-Mandel interference measurement. Despite the effects of photorefraction and pyroelectricity, which can locally alter the phase matching, we achieve cryogenic indistinguishable photons within 1.5 nm of our design wavelength. Our results verify sufficient understanding and control of the cryogenic nonlinear process, which has wider implications when combining quasi-phase-matched nonlinear optical processes with other cryogenic photonic quantum technologies, such as superconducting detectors.

Automated summary

We have demonstrated the generation of degenerate photon pairs through spontaneous parametric down-conversion in titanium-indiffused waveguides in cryogenic temperatures. A precise empirical model of refractive indices was used to fabricate a fixed poling period due to the inability to temperature tune the phase matching inside a cryostat. By designing the phase-matching properties of the periodic poling, we achieved cryogenic indistinguishable photons at 1559.3(6) nm, despite the potential effects of photorefraction and pyroelectricity. This research confirms our understanding and control of the cryogenic nonlinear process, which has broader implications for combining nonlinear optical processes with other cryogenic photonic quantum technologies.