23 December 2015 Quantum Memories in Physics Today

Solid crystal doped with rare-earth ions Photo Credit: Kutlu Kutluer

APS\' specialized magazine dedicates a piece on Quantum Memories and their importance in the world of quantum information networks. Physics Today magazine has recently published an article by Dr. Mikael Afzelius, Prof. Nicolas Gisin and ICREA Professor at ICFO Dr. Hugues de Riedmatten on the physics behind quantum memories and their use for quantum networks.

Quantum memories represent an essential building block for the realization of quantum information networks. The ideal carriers of information in these quantum networks are photons since they are easy to entangle in polarization, amplitude and phase, or other degrees of freedom; they are easy to detect; and they can propagate quickly over large distances with little attenuation.

To date, the optical fiber has been the key revolutionizing ingredient for communications. It has granted access to knowledge, and information and provided basic connectivity to the world by creating a communications network of linked computer nodes known as the internet. Today physicists are developing the technologies needed for a quantum version of the information network, which might be used for, among other applications, long distance cryptography, distributed quantum computing, and remote sensing.

In this thorough article, the authors review the physics of quantum memories and their potential use for quantum networks. Quantum memories would act as the nodes where the photons—or rather, their quantum states—are temporarily stored while the system completes some other processing in the network. The quantum state of a photon can be transferred to a single trapped atom or to a bunch of atoms in a gas or solid and be stored for later release on demand. They also discuss the need to implement many distant quantum memories in order to accomplish large quantum-information networks, representing a great challenge for the achievement of entanglement and exchange of information between nodes. They have shown that, although still in a very early stage, quantum memories have made amazing progress over this past decade, positioning themselves to be crucial components of future quantum information networks.

Prof. de Riedmatten, leader of the Quantum Photonics with Solids and Atoms research group at ICFO, conducts research on quantum information science, linking it to quantum optics and nanoscale science. In particular, his group works on quantum control of light-matter interactions between single photons and atomic ensembles.