Fig. 4 | npj Quantum Information

Fig. 4

From: Optical spin locking of a solid-state qubit

Fig. 4

Optical locking of a coherent superposition. a Spin-locking sequence schematic in the rotating frame. The electron, initially in the \({\left|\uparrow \right\rangle }_{z}\) state, is rotated to \(\left|\tilde{\downarrow }\right\rangle ={\left|\downarrow \right\rangle }_{y}\) by the first \(\frac{\pi }{2}\) pulse. The phase of the drive is then jumped by \(\frac{\pi }{2}\): \(\left|\tilde{\downarrow }\right\rangle\) is now an eigenstate of the drive. The system is driven in this configuration for a time \(T\). A final \(\frac{\pi }{2}\) pulse with phase \(\phi\) before the \({\left|\downarrow \right\rangle }_{z}\) readout allows the equatorial spin components to be measured. b Spin locking with \(\Omega =11\ {\rm{MHz}}\) as a function of locking time \(T\), with a readout phase of \(\phi =0(\pi )\) producing the pink (purple) data. The data are presented alongside a Bloch-equation model (black line: spin-locking, grey line: direct Rabi drive) that accounts for the inhomogeneous broadening of \(\sigma =4.8\ {\rm{MHz}}\) and spin decay \({\Gamma }_{1}\). c Spin locking at \(\Omega =16\ {\rm{MHz}}\) as a function of locking time \(T\). Tomography of the state in the \(xy\)-plane is done by varying the phase \(\phi\) of the final \(\frac{\pi }{2}\) pulse over \(4\pi\) after each locking time; the insets depict two such datasets, indicated by colour. We use these data to extract a visibility, fitted with an exponential decay time of \(2.3\pm 0.2\,{\mathrm {\mu {s}}}\) (black line). The corresponding visibility for a direct Rabi drive is plotted alongside (grey line) and exhibits decay on a \(100\)-\({\rm{ns}}\) timescale. Nuclear-field inhomogeneities lead to the oscillations seen in the Rabi visibility, which is partially refocussed at integer multiples of a \(2\pi\) rotation

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