Leakage reduction in fast superconducting qubit gates via optimal control

Max Werninghaus from the IBM team lead by Stefan Filipp and Federico Roy from the USAAR team lead by F. W.-M. have reported an outstanding sevenfold reduction of the leakage rate  in fast superconducting qubits gates via optimal control. This result is the cusp of 15 years of research.

We report the abstract here below:

“Reaching high speed, high fidelity qubit operations requires precise control over the shape of the underlying pulses. For weakly anharmonic systems, such as superconducting transmon qubits, short gates lead to leakage to states outside of the computational subspace. Control pulses designed with open-loop optimal control may reduce such leakage. However, model inaccuracies can severely limit the usability of such pulses. We implemented a closed-loop optimization that simultaneously adapts all control parameters based on measurements of a cost function built from Clifford gates. By parameterizing pulses with a piecewise-constant representation that matches the capabilities of the control hardware we create a 4.16 ns single-qubit pulse with 99.76% fidelity and 0.044% leakage. This is a seven-fold reduction of the leakage rate of the best DRAG pulse we have calibrated at such short durations on the same system.”

you can find the arxiv at this link: https://arxiv.org/abs/2003.05952