Storage of up-converted telecom photons in a doped crystal

TL;DR

This paper demonstrates the first successful storage of up-converted telecom photons at the single-photon level in a doped crystal, combining frequency conversion and quantum memory techniques.

Contribution

It introduces a novel integration of telecom photon up-conversion with atomic frequency comb storage in a doped crystal, achieving high efficiency and signal-to-noise ratio.

Findings

Maximum device efficiency of 22% including optical losses.

Storage and retrieval efficiencies exceeding 20%.

Signal-to-noise ratio over 100 for single-photon inputs.

Abstract

We report on an experiment that demonstrates the frequency up-conversion of telecommunication wavelength single-photon-level pulses to be resonant with a $\mathrm{Pr}^{3+}$:$\mathrm{Y}_2\mathrm{Si}\mathrm{O}_5$ crystal. We convert the telecom photons at $1570\,\mathrm{nm}$ to $606\,\mathrm{nm}$ using a periodically-poled potassium titanyl phosphate nonlinear waveguide. The maximum device efficiency (which includes all optical loss) is inferred to be $\eta_{\mathrm{dev}}^{\mathrm{max}} = 22 \pm 1\,%$ (internal efficiency $\eta_{\mathrm{int}} = 75\pm8\,%$) with a signal to noise ratio exceeding 1 for single-photon-level pulses with durations of up to 560$\,$ns. The converted light is then stored in the crystal using the atomic frequency comb scheme with storage and retrieval efficiencies exceeding $\eta_{\mathrm{AFC}} = 20\,%$ for predetermined storage times of up to $5\,\mu\mathrm{s}$. The retrieved light is time delayed from the noisy conversion process allowing us to measure a signal to noise ratio exceeding 100 with telecom single-photon-level inputs. These results represent the first demonstration of single-photon-level optical storage interfaced with frequency up-conversion.