Radiofrequency cascade readout of coupled spin qubits

TL;DR

This paper introduces a radiofrequency electron-cascade readout method for silicon spin qubits, significantly improving signal-to-noise ratio and enabling fast, coherent spin control in scalable quantum dot arrays.

Contribution

The authors develop a novel dispersive readout technique that enhances sensitivity and demonstrates high-fidelity spin measurement and control in silicon quantum dots.

Findings

Signal-to-noise ratio improved by over 35 dB.

Minimum integration time of 7.6 microseconds achieved.

Demonstrated coherent spin control with dephasing times up to 500 ns.

Abstract

Silicon spin qubits based on metal-oxide-semiconductor (MOS) technology are compatible with semiconductor manufacturing and offer a route to scalable quantum processing. However, spin readout typically relies on proximal charge sensors, which add architectural complexity and limit qubit connectivity. In situ dispersive readout techniques are more compact, which can alleviate these constraints, but exhibit limited sensitivity. Here we report a radiofrequency electron-cascade readout method that enhances the dispersive signal through alternating-current electron co-tunnelling. With this approach, we achieve an enhancement in signal-to-noise ratio of more than $35~$dB, leading to a minimum integration time of $7.6 \pm 0.2~\mu$s. We demonstrate singlet-triplet readout of two-electron spins in a natural silicon planar MOS quantum dot array, and coherent spin control using the exchange interaction, which forms the basis for entangling gates. We find dephasing times of up to $500~$ns and a gate quality factor that exceeds 10.