Heralded quantum entanglement between two crystals

TL;DR

This paper demonstrates heralded quantum entanglement between two separate crystals doped with rare-earth ions, advancing solid-state quantum network nodes and quantum repeater technology.

Contribution

It reports the first observation of heralded entanglement between two separate rare-earth-ion doped crystals using a single photon and quantum state mapping.

Findings

Successful creation of heralded entanglement between two crystals

Entanglement verified by mapping back to optical modes

Potential for solid-state quantum network nodes

Abstract

Quantum networks require the crucial ability to entangle quantum nodes. A prominent example is the quantum repeater which allows overcoming the distance barrier of direct transmission of single photons, provided remote quantum memories can be entangled in a heralded fashion. Here we report the observation of heralded entanglement between two ensembles of rare-earth-ions doped into separate crystals. A heralded single photon is sent through a 50/50 beamsplitter, creating a single-photon entangled state delocalized between two spatial modes. The quantum state of each mode is subsequently mapped onto a crystal, leading to an entangled state consisting of a single collective excitation delocalized between two crystals. This entanglement is revealed by mapping it back to optical modes and by estimating the concurrence of the retrieved light state. Our results highlight the potential of rare-earth-ions doped crystals for entangled quantum nodes and bring quantum networks based on solid-state resources one step closer.