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 circuit depths and providing protection against leakage. We demonstrate high-fidelity quantum control of an always-on exchange-only (AEON) qubit, operated using simultaneous exchange pulses in a triangular quantum dot (QD) array. We use blind randomized benchmarking to characterize the performance of the full AEON single-qubit Clifford gate set, achieving an average Clifford gate fidelity FC1 = 99.86%. Extensions of this work may enable more efficient EO two-qubit entangling gates as well as the implementation of native i-Toffoli gates in Loss-DiVincenzo single-spin qubits. Exchange only qubits encode a logical qubit in three physical spins and are controlled solely by exchange interactions, but their dependence on sequential exchange pulses leads to large gate depths. Here the authors demonstrate high fidelity quantum control of an always on exchange only qubit in a Si/SiGe quantum dot array using simultaneous exchange pulses.

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Nature

Researchers demonstrate high-fidelity quantum control of an always-on exchange-only (AEON) spin qubit operated in a triangular quantum dot array using simultaneous exchange pulses. Unlike conventional exchange-only qubits that use sequential pairwise exchange interactions, the AEON approach activates multiple non-commuting exchange interactions simultaneously, reducing circuit depths and providing leakage protection. Using blind randomized benchmarking, the team achieved an average Clifford gate fidelity of 99.86%. The work opens pathways to more efficient two-qubit entangling gates and native i-Toffoli gate implementations in Loss-DiVincenzo single-spin qubits.

Demonstration of an always-on exchange-only spin qubit