Electron spins in silicon quantum dots provide a promising route towards realizing the large number of coupled qubits required for a useful quantum processor1,2,3,4,5,6,7. For the implementation of quantum algorithms and error detection8,9,10, qubit measurements are ideally performed in a single shot, which is presently achieved using on-chip charge sensors, capacitively coupled to the quantum dots11. However, as the number of qubits is increased, this approach becomes impractical due to the footprint and complexity of the charge sensors, combined with the required proximity to the quantum dots12. Alternatively, the spin state can be measured directly by detecting the complex impedance of spin-dependent electron tunnelling between quantum dots13,14,15. This can be achieved using radiofrequency reflectometry on a single gate electrode defining the quantum dot itself15,16,17,18,19, significantly reducing the gate count and architectural complexity, but thus far it has not been possible to achieve single-shot spin readout using this technique. Here, we detect single electron tunnelling in a double quantum dot and demonstrate that gate-based sensing can be used to read out the electron spin state in a single shot, with an average readout fidelity of 73%. The result demonstrates a key step towards the readout of many spin qubits in parallel, using a compact gate design that will be needed for a large-scale semiconductor quantum processor.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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The authors thank M. House and A. Laucht for discussions and C. Escott for feedback on the manuscript. The authors also acknowledge support from the US Army Research Office (W911NF-17-1-0198), the Australian Research Council (CE170100012) and the NSW Node of the Australian National Fabrication Facility. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the US Government. M.F.G.-Z. is supported by the Horizon 2020 programme through grant agreement no. 688539. B.H. acknowledges support from the Netherlands Organisation for Scientific Research (NWO) through a Rubicon Grant. This work was partly supported by the Winton Fund for the Physics of Sustainability.