Fig. 2: Detecting the x- and y-components of a spin qubit.
From: Universal quantum control of an atomic spin qubit on a surface
a Upper: Pulse sequence composed of a Rabi rotation \(\theta =\varOmega \tau\) about the x-axis (“initialization”; red), followed by a \({\rm{\pi }}/2\) pulse (“projection”; purple) with a phase \(\varphi =0\) (+X pulse) or \(\varphi ={\rm{\pi }}\) (−X pulse). Lower: Corresponding two-step rotations of a Bloch vector on the Bloch sphere. b Rabi measurements without (‘none’) and with the projection pulse (‘+X’ or ‘−X’) (VDC = 50 mV, IDC = 4 pA, VRF = 120 mV), with fits to an exponentially decaying sinusoidal function (red solid curves). \(\varDelta \alpha\) and black solid lines indicate the shifts of Rabi signals induced by different projection pulses. c Pulse sequence similar to a but with the projection pulse of a phase \(\varphi ={\rm{\pi }}/2\) (+Y pulse) or \(\varphi =3{\rm{\pi }}/2\) (−Y pulse), resulting in the Bloch vector in the x-y plane (purple arrows). d Rabi measurements without and with the projection pulse in c (VDC = 50 mV, IDC = 4 pA, VRF = 120 mV), with fits to an exponentially decaying sinusoidal function (red solid curve). Blue solid lines indicate the vertical offsets added to each spectrum. Duration of the \({\rm{\pi }}/2\) pulses is ~ 9 ns.
