Electrical engineering

Physics

Topology (electrical circuits)

Qubit

Subspace topology

Mathematics

Reduction (mathematics)

Macroeconomics

Engineering

Artificial intelligence

Economics

Control (management)

Transmon

Leakage (economics)

Electronic engineering

Geometry

Computer science

Quantum computer

Quantum mechanics

Control theory (sociology)

Quantum

npj Quantum Information

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. We directly optimize the amplitude and phase of each sample point of the digitized control pulse. We thereby fully exploit the capabilities of the pulse generation electronics and create a 4.16 ns single-qubit pulse with 99.76 % fidelity and 0.044 % leakage. This is a sevenfold reduction of the leakage rate and a threefold reduction in standard errors of the best DRAG pulse we have calibrated at such short durations on the same system.

Leakage reduction in fast superconducting qubit gates via optimal control