Single-shot readout of the nuclear spin in on-surface atoms using ESR-STM

Individual nuclear spins are promising candidates for quantum memory due to enhanced lifetimes and coherence times compared to electronic spins. Most studies have focused on individual nuclear spins embedded in solids and single-molecule magnets, which have limited controllability because of their environments. In contrast, spins in individual atoms on surfaces can be precisely manipulated at the atomic scale using scanning tunneling microscopy (STM). Recently, nuclear spins in individual atoms have been identified by STM equipped with electron spin resonance (ESR) via the hyperfine interaction. However, time-resolved measurements for the relevant timescales have not been reported. In this work, we achieve single-shot readout of the nuclear spin of ⁴⁹Ti atom (S = 1/2 and I = 7/2) adsorbed on MgO/Ag using ESR-STM. We apply radio-frequency (RF) pulses to the ⁴⁹Ti atom at the tunneling junction that drives ESR only if the nuclear spin is in a certain state (e.g., m_I = -7/2). We then determine whether ESR is driven or not by measuring DC tunneling conductance. This new approach enables time-resolved measurements of the nuclear spin state, revealing its lifetime of 5.3 ± 0.5 seconds — seven orders of magnitude longer than the electronic spin in the same atom. Furthermore, by applying DC or RF voltages between the pulses, we demonstrate that the nuclear spin is pumped and relaxed by DC spin-polarized current and ESR driving, respectively, through a flip-flop quantum tunneling channel. The combination of the long timescale of the nuclear spin, its controllability, and STM tip movements between different atoms opens possibilities for simultaneous coherent operations on extended atomic structures comprising multiple spins.