Quantum bits (or qubits) made from single atoms in semiconductors are a promising platform for large-scale quantum computers, thanks to their long-lasting stability. To perform logic operations, two atom-size qubits must be placed very close together, which makes it challenging to squeeze in all the electrodes and sensors needed for qubit control and readout. One solution is to use the control electrodes not only for qubit manipulation but also for sensing the state of the qubit spin state by applying a small oscillating radio frequency (rf) electric field to the electrode. However, the sensitivity has not yet been high enough to measure electron spin states in real time. Here, we demonstrate a paradigm shift for scaling up semiconductor qubits that allows one to read an electron spin with one measurement (aka “single shot”) without the need to repeat the experiment and average the outcomes.

In our approach, an rf signal attempts to move pairs of electrons between dots, but this motion is only possible for certain combinations of electron spins. If the attempt is successful, the motion of charge drives a signal in a resonator attached to one of the gates. We show that this approach allows us to sense the spin state in a single shot with readout fidelities of 82%, and it does so without affecting the spin dynamics during the measurement.

This demonstration confirms that single-gate rf sensing of electron spins is reaching the sensitivity required to perform the necessary quantum error correction in a scalable quantum computer.