Controlled-Z Gates via Floquet Coupling to Two Auxiliary States in Transmon Circuits
Abstract
High-fidelity entangling gates are essential for quantum information processing. In transmon circuits, higher excited states provide additional pathways for engineering interactions within the computational subspace. Here we demonstrate controlled-Z (CZ) gates that exploit two noncomputational states, ket02 and ket20, through selective Floquet coupling. The nontrivial parametric modulation can activate both auxiliary transitions from ket11 while suppressing the leading exchange between ket01 and ket10. Based on this approach, we develop two gate protocols: a nonadiabatic round trip through a bright auxiliary superposition and adiabatic evolution along a zero-energy dark state, both achieving average gate fidelities above 99.99% in numerical simulations. Control of the modulation phase further extends the bright-state protocol to conventional and unconventional geometric CZ gates. Effective-model simulations show that unconventional control improves tolerance to residual ZZ coupling and static qubit-frequency offsets relative to conventional control over the parameter ranges examined. Simulations including neighboring spectator qubits show that the original nonadiabatic bright-state and adiabatic dark-state CZ protocols retain high gate fidelities. This framework offers new routes toward the experimental realization of CZ gates and their geometric implementations.
Related
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- Shaping of the finite-size chaos crossover in Floquet circuits by coherent-mismatch architecture
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BibTeX
@misc{chen2026controlledz,
title = {{Controlled-Z Gates via Floquet Coupling to Two Auxiliary States in Transmon Circuits}},
author = {Yutao Chen and Jia-Chi Zhang and Tian-Ming Li and Yu Liu and Kai Xu and Heng Fan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27834},
eprint = {2610.27834},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27834},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Controlled-Z Gates via Floquet Coupling to Two Auxiliary States in Transmon Circuits
AU - Yutao Chen
AU - Jia-Chi Zhang
AU - Tian-Ming Li
AU - Yu Liu
AU - Kai Xu
AU - Heng Fan
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.27834
UR - https://arxiv.org/abs/2610.27834
AB - High-fidelity entangling gates are essential for quantum information processing. In transmon circuits, higher excited states provide additional pathways for engineering interactions within the computational subspace. Here we demonstrate controlled-Z (CZ) gates that exploit two noncomputational states, ket02 and ket20, through selective Floquet coupling. The nontrivial parametric modulation can activate both auxiliary transitions from ket11 while suppressing the leading exchange between ket01 and ket10. Based on this approach, we develop two gate protocols: a nonadiabatic round trip through a bright auxiliary superposition and adiabatic evolution along a zero-energy dark state, both achieving average gate fidelities above 99.99% in numerical simulations. Control of the modulation phase further extends the bright-state protocol to conventional and unconventional geometric CZ gates. Effective-model simulations show that unconventional control improves tolerance to residual ZZ coupling and static qubit-frequency offsets relative to conventional control over the parameter ranges examined. Simulations including neighboring spectator qubits show that the original nonadiabatic bright-state and adiabatic dark-state CZ protocols retain high gate fidelities. This framework offers new routes toward the experimental realization of CZ gates and their geometric implementations.
ER -