Quantum frequency conversion of memory-compatible single photons from 606 nm to the telecom C-band

TL;DR

This paper demonstrates high-quality quantum frequency conversion of narrow-bandwidth, memory-compatible photons from 606 nm to 1552 nm, maintaining non-classical correlations and low noise, facilitating integration of quantum memories with telecom networks.

Contribution

It introduces a single-step difference frequency generation process for converting 606 nm photons to telecom wavelengths while preserving quantum properties and achieving high signal-to-noise ratio.

Findings

High SNR (>100) in single-photon conversion after spectral filtering.

Preservation of non-classical correlations post-conversion.

Heralded autocorrelation function measured at 0.19±0.07.

Abstract

We report on quantum frequency conversion of memory-compatible narrow-bandwidth photons at 606 nm to the telecom C-band at 1552$\,$nm. The 200$\,$ns long photons, compatible with Praseodymium-based solid-state quantum memories are frequency converted using a single-step difference frequency generation process in a periodically poled Lithium Niobate waveguide. We characterize the noise processes involved in the conversion and by applying strong spectral filtering of the noise, we demonstrate high signal-to-noise ratio conversion at the single photon level (SNR$\,>\,$100 for a mean input photon number per pulse of 1). We finally observe that a memory compatible heralded single photon with a bandwidth of 1.8$\,$MHz, obtained from a spontaneous parametric down conversion pair source, still shows a strong non-classical behavior after conversion. We first demonstrate that correlations between heralding and converted heralded photons stay in the non-classical regime. Moreover, we measured the heralded autocorrelation function of the heralded photon using the converter device as a frequency-domain beam splitter, yielding a value of $0.19\pm0.07$. The presented work represents a step towards the connection of several quantum memory systems emitting narrow-band visible photons to the telecommunication wavelengths.