Polarization insensitive frequency conversion for an atom-photon entanglement distribution via a telecom network

TLDR

Quantum networks rely on telecom photonic infrastructure but lack quantum memories capable of storing arbitrary states long enough for long‑distance communication; atomic memories can store for sub‑second times (~1000 km transmission), yet they cannot directly interact with telecom photons, so solid‑state quantum frequency converters bridge this wavelength gap and enable frequency multiplexing. The study demonstrates a polarization‑insensitive solid‑state quantum frequency conversion that maps a short‑wavelength photon entangled with an atomic ensemble to the telecom band. The conversion uses a nonlinear‑crystal‑based frequency converter inside a Sagnac interferometer to translate the entangled photon while preserving its entanglement. The experiment shows that atom‑photon entanglement is retained after conversion, confirming the feasibility of integrating atomic ensembles with telecom networks.

Abstract

Quantum network with a current telecom photonic infrastructure is deficient in quantum storages that keep arbitrary quantum state in sufficient time duration for a long-distance quantum communication with quantum repeater algorithms. Atomic quantum storages have achieved subsecond storage time corresponding to 1000 km transmission time for a telecom photon through a quantum repeater algorithm. However, the telecom photon is not directly accessible to typical atomic storages. Solid state quantum frequency conversions fill this wavelength gap and add more abilities, for example, a frequency multiplex. Here we report on the experimental demonstration of a polarization-insensitive solid-state quantum frequency conversion to a telecom photon from a short-wavelength photon entangled with an atomic ensemble. Atom-photon entanglement has been generated with a Rb atomic ensemble and the photon has been translated to telecom range while retaining the entanglement by our nonlinear-crystal-based frequency converter in a Sagnac interferometer.