Fig. 2

Coherent single-spin control with ST readout. a Schematic energy level diagram of the (1,3)–(0,4) anti-crossing. b Partial pulse sequences for the coherent spin control experiments in d–f. The sequences start with initializing the system in the (0,4) S state by pulsing from point A to point B (see Fig. 1c). Then, we prepare a \(\left|\uparrow \downarrow \right\rangle\) by moving from point B to point C. As indicated by the curved colour-graded arrow, we pulse diabatically across the S-\(\left|\downarrow \downarrow \right\rangle\) anti-crossing, but adiabatically with respect to all the other anti-crossings²². We then apply the microwave control pulses at the deep detuning point C to manipulate the individual spins. After spin manipulation, we perform readout by converting \(\left|\uparrow \downarrow \right\rangle\) back into singlet and \(\left|\uparrow \uparrow \right\rangle\) and \(\left|\downarrow \downarrow \right\rangle\) into triplet, by pulsing from point C back to the standard PSB region B. The \(\left|\downarrow \uparrow \right\rangle\) state is not accessed during this measurement. c The two ESR peaks plotted as a function of detuning \(\epsilon\). We use an incoherent ESR pulse of 100 μs for this experiment. We identify the lower (higher) frequency peak corresponding to the QD1 (QD2) through the Stark-shift measurements described in ref. ¹. d–f Coherent spin control of QD2 showing d, Rabi oscillations, e, Rabi chevron, and f, Ramsey fringes. We use frequency mixing to implement the ESR pulse scheme. \(\Delta f\) corresponds to the single-sideband modulation of the microwave source. The main carrier frequency of the microwave source is set to 4.2 GHz for d and 12.6 GHz for e, f. We extract the tunnel coupling in the shallow detuning region (\(\epsilon \approx 3\) meV) to be \(2.0\pm 0.2\) GHz from c. We performed all the single qubit operations in the deep detuning region (\(\epsilon \approx 24\) meV) where the tunnel coupling between the two qubits is negligibly small.