We posted three preprints describing recent work on quantum control of high anharmonicity flux quantum circuits. This work is based on a new design of a capacitively shunted flux circuit (https://arxiv.org/abs/2008.00593 ) that combines large level anarhmonicity and long energy relaxation times. We characterized the coherence in the qubit subspace; we find energy relaxation times of about 40 us and dephasing times with dynamical decoupling in the tens of microsecond range. We also characterized decoherence in the subspace of the lowest three states of the system.
We implemented a qutrit fundamental gate – the Walsh Hadamard gate using a new approach based on a single pulse decomposition enabled by simultanous driving of all transitions in the qutrit (https://arxiv.org/abs/2003.04879 ), with a high fidelity of 99.2 %.
More recently, we demonstrated randomized benchmarking characterization of control of the qutrit (https://arxiv.org/abs/2009.00599). Randomized benchmarking is routinely used in qubit gate characterization. This work is a demonstration of benchmarking for a qutrit. It is enabled by the application of a universal gate decomposition method for qudits. The work sheds new light on control issues that are unique to multileve systems and opens new avenues for control of qutrits.