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

Abstract

Proposals for large-scale semiconductor spin-based quantum computers require high-fidelity singleshot 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.

Noisy intermediate-scale quantum computers

“…Also, to improve the signal-to-noise ratio (SNR), quantum noise-limited JPA [566] and other amplification methods were combined. Multiple spin readout has been shown with a single electron box [567] and done by frequency multiplexing [568]. Several teams have already demonstrated enhanced readout fidelities for S-T qubits and spin qubits in a non-demolition method [569,570], which shall find their importance in fault-tolerant computing and in studying spin state collapse problems for fundamental quantum mechanics.…”