Single-shot single-electron spin readout with a single-lead quantum dot charge sensor

“Gate-based”, or dispersive, charge sensors for the readout of semiconductor spin qubits have been growing in popularity because these compact sensors integrate readout capability into electrical control structures. However, dispersive readout can only directly measure a spin state in a double quantum dot, either by Pauli blockade or with a large magnetic field gradient. Here we demonstrate a dispersively-probed single-lead quantum dot (SLQD) charge sensor which senses the charges on four quantum dots, each defined with P atoms in Si using scanning tunnelling microscope lithography. With this charge sensor we demonstrate single-shot, single-spin readout via energy-selective tunnelling. We achieve a voltage signal-to-noise ratio of 8 for charge detection with a measurement bandwidth of 15 kHz and demonstrate spin readout with high fidelities of up to 97.4% at 2.5 Tesla. The capacitive coupling between all four quantum dots and the charge sensor is strong enough that there is no loss of sensitivity for detecting the more distant quantum dots, up to about 100 nm away from the sensor. Good sensitivity, compact geometry, and long-range sensing makes the SLQD a promising choice of sensor for scaling up future atomic-precision single-spin qubit devices to larger numbers of qubits.