# Quantum correlations between single telecom photons and a multimode on-demand solid state quantum memory

## TL;DR

This paper demonstrates the first multimode on-demand solid state quantum memory that can store and retrieve telecom photons, establishing a key step towards scalable quantum networks with solid-state nodes.

## Contribution

It introduces a novel multimode on-demand quantum memory in a solid state system capable of storing telecom photons, advancing quantum network technology.

## Key findings

- Successful storage and retrieval of telecom photons in a solid state quantum memory.
- First demonstration of a multimode on-demand quantum memory for external quantum states.
- Potential application in quantum repeaters and large-scale quantum networks.

## Abstract

Quantum correlations between long lived quantum memories and telecom photons that can propagate with low loss in optical fibers are an essential resource for the realization of large scale quantum information networks. Significant progress has been realized in this direction with atomic and solid state systems. Here, we demonstrate quantum correlations between a telecom photon and a multimode on-demand solid state quantum memory. This is achieved by mapping a correlated single photon onto a spin collective excitation in a Pr$^{3+}$:Y$_2$SiO$_5$ crystal for a controllable time. The stored single photons are generated by cavity enhanced spontaneous parametric down conversion (SPDC) and heralded by their partner photons at telecom wavelength. These results represent the first demonstration of a multimode on-demand solid state quantum memory for external quantum states of light. They provide an important resource for quantum repeaters and pave the way for the implementation of quantum information networks with distant solid-state quantum nodes.