Storage of hyperentanglement in a solid-state quantum memory

TL;DR

This paper demonstrates the successful storage and retrieval of hyperentangled photons in a solid-state quantum memory, enabling long-distance quantum communication and advanced quantum information processing.

Contribution

It is the first to experimentally show quantum storage of hyperentanglement in a solid-state memory, combining polarization and energy-time degrees of freedom.

Findings

Violations of Bell inequality for each degree of freedom after storage.

Compatible with long-distance quantum communication in optical fibre.

Suitable for entanglement purification in quantum repeaters.

Abstract

Two photons can simultaneously share entanglement between several degrees of freedom such as polarization, energy-time, spatial mode and orbital angular momentum. This resource is known as hyperentanglement, and it has been shown to be an important tool for optical quantum information processing. Here we demonstrate the quantum storage and retrieval of photonic hyperentanglement in a solid-state quantum memory. A pair of photons entangled in polarization and energy-time is generated such that one photon is stored in the quantum memory, while the other photon has a telecommunication wavelength suitable for transmission in optical fibre. We measured violations of a Clauser-Horne-Shimony-Holt (CHSH) Bell inequality for each degree of freedom, independently of the other one, which proves the successful storage and retrieval of the two bits of entanglement shared by the photons. Our scheme is compatible with long-distance quantum communication in optical fibre, and is in particular suitable for linear-optical entanglement purification for quantum repeaters.