Fig. 2: Single-shot readout of the QD spin at 2.0 T.

a Example single-shot readout traces. If a photon is detected during the readout pulse, the state of the QD is assigned to the bright state (here, spin up \(\left|\!\! \uparrow \right\rangle\)). Repetitions with no detected photon are assigned to the dark state (here, spin down \(\left|\!\! \downarrow \right\rangle\)). Schematic of the QD energy levels in a magnetic field, indicating the readout transition (here, bright state \(\left|\!\! \uparrow \right\rangle\), blue arrow) and the cavity frequency. b Frequency configuration of the two QD transitions and mode-split cavity with respect to the laser. With a 2.0 T magnetic field, only one trion transition is resonant with the H-polarised cavity mode, resulting in spin-selective Purcell enhancement. c, d Experimental count fraction (top) and corresponding readout fidelity/errors (bottom) as a function of readout time for the bright state being up/down. Here, readout pulses with a duration of 5 ns are used. The pulse sequence is repeated 100,000 times. We achieve a readout fidelity of 95.2% for a readout time of 3 ns.