Progress toward a quantum processor testbed based on nitrogen-vacancy centers in diamond

The negatively-charged nitrogen-vacancy (NV) center in diamond, consisting of a substitutional nitrogen atom and an adjacent vacancy defect, can provide a platform for quantum registers of at least 10 qubits [1]. The NV center has many useful properties such as optical addressability and long spin-coherence times even at room temperature. We describe a new NV-based quantum computing testbed at the University of Washington. A solid immersion lens is fabricated in the diamond above a single NV center for enhanced light collection with a cryogenic confocal microscope, allowing for single-shot readout of the electronic spin state. We use a combination of two permanent magnets, one fixed magnet inside the cryostat and another adjustable magnet outside the cryostat for precise alignment of the magnetic field to the NV-axis. Finally, we describe the design and fabrication of a radio-frequency antenna on the diamond substrate to optimize couplings to the NV-center electronic spin and nearby nuclear spins. The testbed will be used to implement quantum protocols and small-scale quantum algorithms for both pedagogical and research purposes.

[1] Bradley, C. E. et al. A 10-qubit solid-state spin register with quantum memory up to one minute. Phys. Rev. X 9, 031045 (2019).