Fig. 1: Experimental setup and coherent control of a spin qubit.
From: Universal quantum control of an atomic spin qubit on a surface
a Experimental setup. A vector RF generator is gated by an AWG, and the phase-controlled RF signal is fed into the STM. An external magnetic field ~0.6 T is applied along the sample in-plane direction. Single titanium (Ti) atoms (with an attached H atom) at oxygen sites of bilayer MgO (S = 1/2) are studied in this work, as shown in the STM image of a size 3 × 3 nm2 (tunneling conditions: VDC = 100 mV, IDC = 10 pA). b Schematic illustrating a single-qubit rotation \({{\bf{R}}}_{\varphi }(\theta )\) of \(\theta =\varOmega \tau\) about an axis of angle φ from the x-axis. On the Bloch sphere, the north and south poles represent the qubit’s \(\left|0\right\rangle\) (ground) and \(\left|1\right\rangle\) (excited) states, respectively. The angle φ is determined by the phase difference φ of two consecutive RF pulses in the following experiments. Ω and τ are the Rabi rate and duration of the RF pulse, respectively. c ESR spectrum of a Ti atom (VDC = 50 mV, IDC = 4 pA, VRF = 60 mV). Solid curve is a Lorentzian fit which yields a resonance frequency f0 = 15.25 GHz. d Rabi oscillations measured with increasing pulse duration τ at f0 (VDC = 50 mV, IDC = 4 pA, VRF = 90 mV).
