Fig. 4: Real-time-controlled exchange-driven qubit rotations.
a One repetition of the exchange rotation protocol. After estimation of ΩL and ΩH as in Fig. 3, the OPX adjusts exchange duration times \({\tilde{t}}_{l}\), using real-time knowledge of 〈ΩH〉, to rotate the qubit by user-defined target angles \({\theta }_{l}={\tilde{t}}_{l}\,\langle {{{\Omega }}}_{{{{{{{{\rm{H}}}}}}}}}\rangle\). Pulse durations \({\tilde{t}}_{\pi /2}\) for qubit initialization and readout use real-time knowledge of 〈ΩL〉. b Each row plots measurements mj from one protocol repetition, here M = 101 exchange probe outcomes. c Each row plots measurement ml from one protocol repetition, here K = 101 controlled-exchange-rotation outcomes. To illustrate the increased coherence of controlled exchange rotations, we also plot in b and c the fraction of singlet outcomes of each column.
