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arXiv · 2103.15681

Two-qubit sweet spots for capacitively coupled exchange-only spin qubits

MengKe Feng·Lin Htoo Zaw·Teck Seng Koh
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Abstract

The implementation of high fidelity two-qubit gates is a bottleneck in the progress towards universal quantum computation in semiconductor quantum dot qubits. We study capacitive coupling between two triple quantum dot spin qubits encoded in the $S = 1/2$, $S_z = -1/2$ decoherence-free subspace -- the exchange-only (EO) spin qubits. We report exact gate sequences for CPHASE and CNOT gates, and demonstrate theoretically, the existence of multiple two-qubit sweet spots (2QSS) in the parameter space of capacitively coupled EO qubits. Gate operations have the advantage of being all-electrical, but charge noise that couple to electrical parameters of the qubits cause decoherence. Assuming noise with a 1/f spectrum, two-qubit gate fidelities and times are calculated, which provide useful information on the noise threshold necessary for fault-tolerance. We study two-qubit gates at single and multiple parameter 2QSS. In particular, for two existing EO implementations -- the resonant exchange (RX) and the always-on exchange-only (AEON) qubits -- we compare two-qubit gate fidelities and times at positions in parameter space where the 2QSS are simultaneously single-qubit sweet spots (1QSS) for the RX and AEON. These results provide a potential route to the realization of high fidelity quantum computation.

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MengKe Feng, Lin Htoo Zaw, Teck Seng Koh. 2021-03-29. Two-qubit sweet spots for capacitively coupled exchange-only spin qubits. https://doi.org/10.1038/s41534-021-00449-4

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