Single-atom qubits on a surface: pulsed electron spin resonance in a scanning tunneling microscope
Recently, the ability to drive electron spin resonance (ESR) of individual atoms using a scanning tunneling microscope (STM) provides a major step forward in sensing and manipulating magnetism at the atomic scale. In the first part, I will describe the implementation of continuous-wave ESR in STM , which has allowed the measurement of the magnetic interaction between individual atoms [2–5] as well as the detection and control of nuclear spins [6, 7]. Next, I will talk about coherent spin rotations of individual atoms on a surface with control at the nanosecond timescale, using all-electric pulsed ESR in STM. By modulating the atomically-confined magnetic interaction between the STM tip and surface atoms [8, 9], the large oscillating electric field in the STM junction induces quantum Rabi oscillations between spin-up and spin-down states in as little as ~20 nanoseconds . Ramsey fringes and spin echo signals allow us to understand and improve quantum coherence. I will also show the coherent operations on the coupled-spin states of engineered atomic dimers. Coherent control of spins arranged with atomic precision provides a solid-state platform for quantum simulation of many-body systems.  Baumann et al., Science 350, 417 (2015).  Choi et al., Nat. Nanotechnol. 12, 420 (2017).  Natterer et al., Nature 543, 226 (2017).  Yang et al., Phys. Rev. Lett. 119, 227206 (2017).  Bae et al., Sci. Adv. 4, eaau4159 (2018).  Willke et al., Science 362, 336 (2018).  Yang et al., Nat. Nanotechnol. 13, 1120 (2018).  Lado et al., Phys. Rev. B 96, 205420 (2017).  Yang et al., Phys. Rev. Lett. 122, 227203 (2019).  Yang et al., Science 366, 509 (2019). *We acknowledge financial support from the Office of Naval Research.