A Scalable Quantum Network based on Individual Erbium Ions

ended

A future quantum network will consist of quantum processors that are connected by quantum channels, just like conventional computers are wired up to form the Internet. In contrast to classical devices, however, the entanglement and non-local correlations available in a quantum-controlled system facilitate novel fundamental tests of quantum theory and numerous applications in distributed quantum information processing, quantum communication, and precision measurement. While pioneering experiments have demonstrated the entanglement of two quantum nodes separated by up to 1.3 km, accessing the full potential of quantum networks requires scaling of these prototypes to more nodes and larger distances. To this end, a new technology that overcomes the bottlenecks of existing physical systems has to be developed. Here, I propose to harness the exceptional properties of individual Erbium ions embedded in Yttrium crystals to increase the size of quantum networks via implementation of the seminal quantum repeater proposal, which is one of the most intensively pursued research topics in current quantum science. The key proposed steps to this goal are (I) implementation of a quantum spin-photon interface at a telecommunication wavelength, (II) multiplexing of many quantum bits in one device via frequency-selective addressing, and (III) implementation of remote entanglement swapping and purification to increase the range of quantum-secure communication beyond its current fundamental limit. These goals have been out of reach for any experimental platform until now. They become feasible by combining the powerful concepts developed in cavity quantum electrodynamics using cold atoms with the exceptional coherence of spins in specific host crystals. Successful implementation will demonstrate the feasibility of quantum networks over global distances, a milestone advancement for quantum communication and quantum science in general.