Expérimental
Utilizing superconducting circuits as a resource for quantum information processing, circuit Quantum ElectroDynamics (cQED) has made incredible advances in recent years, but still faces enormous challenges in scaling and most devices are limited to sub-millisecond coherence times. Using the spin of a defect in a crystalline substrate as a qubit promises access to thousands of qubits with coherence times of seconds or more, but such systems lack the fast addressability and level of control available with cQED. A hybrid architecture, using superconducting circuits to control and read out an impurity spin in a crystal lattice, leverages the advantage of both. With recent advances in superconducting single microwave photon detectors (SMPDs), the detection of spins via their fluorescence into a superconducting resonator has enabled single-spin detection and coherent manipulation. We aim to use a single electron spin of an Er ion to control and read out a register of neighbouring nuclear spins naturally present in the CaWO4 host lattice with coherence times exceeding seconds. This will involve demonstrating high fidelity two-qubit gates between nuclear spins and quantum non-demolition readout via the electron spin. Such a system offers the possibility to implement quantum algorithms such as error correction, or to explore waveguide QED via coherent emission of highly entangled photonic quantum states into the resonator.