Quantum frequency conversion of quantum memory compatible photons to telecommunication wavelengths

TL;DR

This paper demonstrates quantum frequency conversion of photons compatible with atomic quantum memories to telecom wavelengths using a PPLN waveguide, achieving high efficiency and fidelity suitable for quantum communication.

Contribution

It presents the first experimental realization of converting quantum memory-compatible photons to telecom wavelengths with high efficiency and fidelity, suitable for quantum networks.

Findings

Conversion efficiency up to 41% internally

Good signal-to-noise ratio at single-photon level

Successful quantum regime operation with high qubit fidelity

Abstract

We report an experiment demonstrating quantum frequency conversion of weak light pulses compatible with atomic quantum memories to telecommunication wavelengths. We use a PPLN nonlinear waveguide to convert weak coherent states at the single photon level with a duration of 30ns from a wavelength of 780nm to 1552nm. We measure a maximal waveguide internal (external) conversion efficiency eta_int = 0.41 (eta_ext = 0.25), and we show that the signal to noise ratio (SNR) is good enough to reduce the input photon number below 1. In addition, we show that the noise generated by the pump beam in the crystal is proportional to the spectral bandwidth of the device, suggesting that narrower filtering could significantly increase the SNR. Finally, we demonstrate that the quantum frequency converter can operate in the quantum regime by converting a time-bin qubit and measuring the qubit fidelity after conversion.