Single-shot readout of multiple donor electron spins with a gate-based sensor

TL;DR

This paper demonstrates high-fidelity single-shot readout of multiple donor electron spins using a compact, gate-based nanoscale sensor in silicon, enabling scalable quantum computing with reduced sensor density.

Contribution

It introduces a novel, all-epitaxial silicon donor-based sensor capable of reading multiple qubits with high fidelity, reducing the sensor footprint and increasing scalability.

Findings

Achieved 95% fidelity in single-shot readout of three qubits.

Observed a 1/d^{1.4} capacitive coupling scaling, better than traditional devices.

Estimated potential to read approximately 15 qubits with a single sensor.

Abstract

Proposals for large-scale semiconductor spin-based quantum computers require high-fidelity single-shot qubit readout to perform error correction and read out qubit registers at the end of a computation. However, as devices scale to larger qubit numbers integrating readout sensors into densely packed qubit chips is a critical challenge. Two promising approaches are minimising the footprint of the sensors, and extending the range of each sensor to read more qubits. Here we show high-fidelity single-shot electron spin readout using a nanoscale single-lead quantum dot (SLQD) sensor that is both compact and capable of reading multiple qubits. Our gate-based SLQD sensor is deployed in an all-epitaxial silicon donor spin qubit device, and we demonstrate single-shot readout of three $^{31}$P donor quantum dot electron spins with a maximum fidelity of 95%. Importantly in our device the quantum dot confinement potentials are provided inherently by the donors, removing the need for additional metallic confinement gates and resulting in strong capacitive interactions between sensor and donor quantum dots. We observe a $1/d^{1.4}$ scaling of the capacitive coupling between sensor and $^{31}$P dots (where $d$ is the sensor-dot distance), compared to $1/d^{2.5-3.0}$ in gate-defined quantum dot devices. Due to the small qubit size and strong capacitive interactions in all-epitaxial donor devices, we estimate a single sensor can achieve single-shot readout of approximately 15 qubits in a linear array, compared to 3-4 qubits for a similar sensor in a gate-defined quantum dot device. Our results highlight the potential for spin qubit devices with significantly reduced sensor densities.