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 constrains, 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 ± 0.2 µs. 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. A dispersive sensing technique, termed the radiofrequency electron cascade, can perform singlet-triplet readout of two exchange-coupled electron spins in a natural silicon planar metal–oxide–semiconductor quantum-dot array.

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Nature

Researchers demonstrate a new dispersive readout technique called the radiofrequency (rf) electron cascade for silicon spin qubits in a planar MOS quantum dot array. By introducing a third quantum dot coupled to a charge reservoir that amplifies the AC polarizability signal through co-tunnelling, the method achieves a signal-to-noise ratio enhancement exceeding 35 dB and a minimum integration time of 7.6 µs — more than two orders of magnitude faster than previous planar MOS dispersive readout results. The technique enables singlet-triplet readout of two-electron spins while retaining the non-demolition nature of in situ dispersive measurements. Exchange control between spin qubits is also demonstrated, with dephasing times up to 500 ns and a gate quality factor exceeding 10, forming the basis for entangling gates. The approach is proposed as scalable to 2D qubit arrays via frequency-multiplexed cascade chains.

Radiofrequency cascade readout of coupled spin qubits