Abstract
The readout of semiconductor spin qubits based on spin blockade is fast but suffers from a small charge signal. Previous work suggested large benefits from additional charge mapping processes, however uncertainties remain about the underlying mechanisms and achievable fidelity. In this work, we study the single-shot fidelity and limiting mechanisms for two variations of an enhanced latching readout. We achieve average single-shot readout fidelities > 99.3% and > 99.86% for the conventional and enhanced readout respectively, the latter being the highest to date for spin blockade. The signal amplitude is enhanced to a full one-electron signal while preserving the readout speed. Furthermore, layout constraints are relaxed because the charge sensor signal is no longer dependent on being aligned with the conventional (2, 0) - (1, 1) charge dipole. Silicon donor-quantum-dot qubits are used for this study, for which the dipole insensitivity substantially relaxes donor placement requirements. One of the readout variations also benefits from a parametric lifetime enhancement by replacing the spin-relaxation process with a charge-metastable one. This provides opportunities to further increase the fidelity. The relaxation mechanisms in the different regimes are investigated. This work demonstrates a readout that is fast, has one-electron signal and results in higher fidelity. It further predicts that going beyond 99.9% fidelity in a few microseconds of measurement time is within reach.
Highlights
There is a rapidly growing commercial interest in quantum computing for applications such as optimization and quantum chemistry
The device is electrically biased to form a single-electron transistor (SET) in the upper wire, which is used as a charge sensor (CS), and a few-electron QD in the lower wire
We demonstrate that the enhanced latching readout (ELR) can achieve higher fidelities than the Pauli spin-blockade (PSB) readout using optimized device parameters and a different donor, called donor 2
Summary
There is a rapidly growing commercial interest in quantum computing for applications such as optimization and quantum chemistry. Quantum-dot (QD) spin qubits are of interest because of their promising coherence properties, the solid-state all-electrical control that can be achieved, and the potential to be built on the semiconductor fabrication platform already used for high-performance computing. Qubit control fidelities have been studied extensively and have reached relatively low error probabilities [3,4,5,6,7,8]. State preparation and readout errors have yet to reach low error levels [8,9,10,11,12]. Even though faulttolerance thresholds lie at the 1% level for one error correction round, individual components need to be much better (approximately 0.1% error probability or better)
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