# Quantum optical frequency up-conversion for polarisation entangled qubits: towards interconnected quantum information devices

## TL;DR

This paper demonstrates a noise-free, polarization-preserving quantum frequency converter that links telecom photons to near-infrared quantum memories, advancing interconnected quantum networks.

## Contribution

The authors develop a robust, guided-wave quantum frequency conversion device that preserves polarization and entanglement, enabling integration of diverse quantum systems.

## Key findings

- Near-perfect single photon state transfer after conversion
- High-fidelity entanglement preserved through frequency conversion
- Device is compact, robust, and adaptable to various wavelengths

## Abstract

Realising a global quantum network requires combining individual strengths of different quantum systems to perform universal tasks, notably using flying and stationary qubits. However, transferring coherently quantum information between different systems is challenging as they usually feature different properties, notably in terms of operation wavelength and wavepacket. To circumvent this problem for quantum photonics systems, we demonstrate a polarisation-preserving quantum frequency conversion device in which telecom wavelength photons are converted to the near infrared, at which a variety of quantum memories operate. Our device is essentially free of noise which we demonstrate through near perfect single photon state transfer tomography and observation of high-fidelity entanglement after conversion. In addition, our guided-wave setup is robust, compact, and easily adaptable to other wavelengths. This approach therefore represents a major building block towards advantageously connecting quantum information systems based on light and matter.