Closed-loop gate-set optimization via quantum optimal control for an ensemble of nitrogen vacancy centers in diamond

Precise control of a quantum system is a prerequisite for quantum information, quantum computing, and quantum metrology. Quantum gates on ensembles of nitrogen vacancy (NV) centers usually suffer from decoherence and other influences from the surrounding spin environment, imperfect state preparation and therefore limited total operation fidelity. Large state preparation and measurement (SPAM) errors cause the typically used quantum process tomography to fail. We explore the applicability of gate set tomography in combination with maximum likelihood estimation and randomized benchmarking for the closed-loop optimization and evaluation of whole gate sets for the usage in e.g. sensing pulse sequences with ensembles of NV centers.