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 [1], 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 [10]. 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.

[1] Baumann et al., Science 350, 417 (2015).
[2] Choi et al., Nat. Nanotechnol. 12, 420 (2017).
[3] Natterer et al., Nature 543, 226 (2017).
[4] Yang et al., Phys. Rev. Lett. 119, 227206 (2017).
[5] Bae et al., Sci. Adv. 4, eaau4159 (2018).
[6] Willke et al., Science 362, 336 (2018).
[7] Yang et al., Nat. Nanotechnol. 13, 1120 (2018).
[8] Lado et al., Phys. Rev. B 96, 205420 (2017).
[9] Yang et al., Phys. Rev. Lett. 122, 227203 (2019).
[10] Yang et al., Science 366, 509 (2019).