Single-shot in situ readout of a spin qubit unit cell.

Spin qubits based on semiconductor quantum dots can offer high coherence times and gate fidelities, and are a potential platform for quantum computation. However, scaling up the number of qubits to the level required for fault-tolerant quantum computing is challenging and will require single-shot, low-footprint qubit readout. Here we report single-shot readout of a spin qubit unit cell using in situ dispersive readout. Our compact, foundry-fabricated unit cell is composed of two electron spins with a controllable exchange interaction, and with it we demonstrate initialization, single-shot readout and a two-electron entangling gate. From exchange oscillations, we extract a spin visibility of 80.7(8)% in the coherent control of a qubit, despite a relatively small lever arm to the resonator gate (less than 0.15(5) eV V-1). We show that the unit cell can be operated at up to 1 K with low charge noise levels, extracted using free induction decay.