Single rare-earth ions in solid state hosts: a testbed for quantum networks and nuclear spin physics

Optically addressed spin defects in solid-state hosts are a versatile platform for studying fundamental physics and building quantum networks. Their microscopic environment is resource-rich containing nuclear and electronic spins, they contain an intrinsic interface to optical photons (ideal carriers of quantum information) and are compatible with scalable device engineering. Rare-earth ions in solid-state hosts have been a mainstay of classical optical communication infrastructure. Their application to quantum information science started with dilute ensemble-based optical quantum memories. However, more recently, coupling to nanophotonic cavities has enabled spectroscopy and quantum control of individual emitters. My talk will focus on the application of one such platform (single ¹⁷¹Yb³⁺ ions in YVO₄) in two contexts:



Firstly, excellent optical and spin coherence properties are leveraged to explore small-scale quantum networking protocols. We demonstrate entanglement between optically distinguishable ions using a single photon heralding protocol. The narrow optical ensemble inhomogeneity provides a unique advantage amongst solid-state systems, enabling quantum connectivity between any pair of ions in a scalable fashion.



Secondly, high-fidelity spin control is leveraged to access local nuclear spins surrounding individual qubits. These spins comprise a dense ensemble which serves as a deterministic quantum resource. We utilise Hamiltonian engineering to generate tailored interactions enabling polarisation, coherent control and preparation of many-body nuclear spin states. We utilise these states as quantum registers and explore decoherence protected subspaces that eliminate the deleterious effect of common-mode noise.



These results showcase single rare-earth ions as a promising platform for the future quantum internet and as an interface to study dense nuclear spin ensembles.