Demonstration of an Always-On Exchange-Only Spin Qubit

In conventional exchange-only (EO) spin qubit demonstrations, quantum gates have been implemented using sequences of individually pulsed pairwise exchange interactions --- with only one exchange coupling active at a time. Alternatively, multiple non-commuting exchange interactions can be pulsed simultaneously, reducing logical gate depths and providing a natural protection against leakage. Here, we demonstrate high-fidelity quantum control of an always-on, exchange-only (AEON) qubit, operated using simultaneous exchange pulses in a triangular quantum dot array [1, 2]. We use blind randomized benchmarking to characterize the performance of the full AEON single-qubit Clifford gate set, achieving an average Clifford gate fidelity of 99.86 %. Extensions of this work could enable more efficient two-qubit EO entanglement gates as well as the implementation of native i-Toffoli gates in Loss-DiVincenzo single spin qubits.

[1] Broz, J. D., Hoke, J. C., Acuna, E., & Petta, J. R. Demonstration of an always-on exchange-only spin qubit. arXiv:2508.01033 (2025).

[2] Acuna, Edwin, et al. "Coherent control of a triangular exchange-only spin qubit." Physical Review Applied 22(4), 044057 (2024).