Fig. 1
All optical ESR of a QD electron spin. a Experimental schematic: Intensity modulation of a single-frequency laser produces two sidebands for spin-control. Encoding a phase step \(\Delta {\phi }_{\mathrm {{\mu {w}}}}\) in the microwave signal produces a change of relative phase \(\phi =2\Delta {\phi }_{\mathrm {{\mu {w}}}}\) between the two sidebands. These then drive two-photon Raman transitions between the energy levels of a negatively charged QD, as shown on the right. The optical fields have a single-photon detuning from the excited state of \({\Delta }_{{\mathrm {L}}}\approx 700\;{\rm{GHz}}\), and a two-photon detuning from the ESR of \(\delta\). A resonant laser pulse is used to initialise the spin via optical pumping prior to spin control and to read out the population of the \(\left|\downarrow \right\rangle\) state after spin control. b Time evolution of \(\left|\downarrow \right\rangle\)-state population after drive time \(T\) taken at three different Rabi frequencies. The solid curves are fits from a Bloch-equation model to extract the Rabi frequency \(\Omega\). c Dependence of the Rabi frequency \(\Omega\) on the laser power incident on the cryostat window. The black line is a linear fit, with a slope of \(13.4\ {\rm{MHz}}.{\mathrm {\mu {{W}}}}^{-1}\)
