Overcoming the Speed-Fidelity Trade-off in Fast CZ Gates via Cyclic Control

• URL: http://arxiv.org/abs/2607.00660v1
• Date: Wed, 01 Jul 2026 09:09:00 GMT
• Title: Overcoming the Speed-Fidelity Trade-off in Fast CZ Gates via Cyclic Control
• Abstract summary: Short-timescale waveform distortions break the time-reflection symmetry of control pulses, preventing the precise closure of cyclic evolution.<n>We introduce a cyclic control strategy based on parameter-space expansion, which restores controllability by incorporating an additional degree of freedom.<n>We experimentally demonstrate this approach in a superconducting controlled-Z gate, achieving robust suppression of coherent errors without increasing gate duration.
• Score: 16.45224279739977
• License: http://creativecommons.org/licenses/by-sa/4.0/
• Abstract: High-fidelity quantum gates are essential for scalable quantum computation. However, at short durations, short-timescale waveform distortions break the time-reflection symmetry of control pulses, preventing the precise closure of cyclic evolution. This mechanism renders conventional symmetric protocols intrinsically over-constrained. Conventional strategies typically rely on smoothing the pulse envelopes or embedding the interaction pulse within a longer qubit pulse to bypass short-timescale distortions, which inevitably leads to a persistent speed-fidelity trade-off. To overcome this limitation, we introduce a cyclic control strategy based on parameter-space expansion, which restores controllability by incorporating an additional degree of freedom. We experimentally demonstrate this approach in a superconducting controlled-Z gate, achieving robust suppression of coherent errors without increasing gate duration, reducing the average coherent error from 0.27% to 0.12% across multiple two-qubit gates, as validated by cross-entropy benchmarking. Our results establish a general route to fast, high-fidelity cyclic quantum gates beyond the conventional speed-fidelity trade-off.

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