A continuous two-qubit gate set for transmon qubits: robust implementation and leakage calibration

Organiser:
Lehrstuhl für Experimentalphysik (Eichler)

Title:
A continuous two-qubit gate set for transmon qubits: robust implementation and leakage calibration

Speaker:
Dr. Christoph Hellings, ETH Zürich

Time, place:
16:00 Thursday, 30 October 2025
Lecture Hall H, Staudtstr. 5

Abstract:

Versatile hardware-native gate sets, including continuous sets of two- qubit gates, can improve the performance of near-term quantum algorithms by reducing the circuit depth. This talk presents a continuous set of controlled-phase gates, which extends prior implementations of two-qubit gates based on resonant interaction between flux-tunable transmon qubits. We present a calibration procedure that makes it possible to parameterize the continuous gate set with a single control parameter, the idle time between the two rectangular halves of the net-zero control pulse. The vanishing time integral of these control pulses provides robustness against memory effects stemming from long-time distortions in flux control lines. As a crucial ingredient to the calibration, we introduce a measurement of the leakage out of the computational subspace based on coherent population amplification. We characterize the continuous gate set with cross-entropy benchmarking for fixed values of the conditional phase and for phases randomly drawn from a uniform distribution. The results confirm a consistently high gate fidelity and low leakage over the full range of conditional phases.