SMERC · Strong Microwave Erbium Coupling

Electronic and nuclear spins in solids have remarkable coherence properties which makes them ideal qubit candidates for future quantum computers. However, microwave detection and coupling of individual spins remains an outstanding challenge, and this is the main obstacle to their use for quantum computing. The rare earth element erbium (Er) is a very promising candidate for single-spin detection due to its exceedingly large electronic ground-state moment (J=15/2). Furthermore, Er has recently demonstrated 1.3 second hyperfine spin coherence (https://arxiv.org/abs/1611.0431), thus joining a very short list of solid state defects with coherence times of over a second. The Strong Microwave Erbium Coupling (SMERC) proposal aims to use superconducting circuits consisting of resonators and Josephson qubits to detect and couple individual Er spins in crystalline matrices.The superconducting circuits will be designed so as to enhance their magnetic coupling to the individual Er spins. In particular, nanoscale constrictions will be used to concentrate the microwave magnetic field at the Er ion location. This will result in Er-microwave photon coupling constants sufficient to detect a single Er spin within less than a millisecond integration time with microwave signals.