[QUANTUM SEMINAR] 2025년 제 4회 - Single-shot readout and coherent driving of nuclear spins in a single atom on surfaces

고려대학교 주관 양자대학원에서는 

7월 3일 Delft University of Technology, 이진원 박사님을 초청하여 "Single-shot readout and coherent driving of nuclear spins in a single atom on surfaces"의 주제로 세미나를 개최했습니다.

Individual nuclear spins are promising candidates for quantum memory due to enhanced lifetimes and coherence times compared to electronic spins. Their single-shot readout and coherent control have been demonstrated in various platforms such as color centers, molecular break junctions, and semiconductors. As hyperfine coupling is sensitively affected by the atomic environment of spins, nuclear spins in on-surface atoms addressed by scanning tunneling microscopy (STM) offer the potential for tuning the hyperfine coupling via atom manipulation, which enables us to study the fundamental nature of their relaxation and decoherence. While recent works have identified nuclear spins in individual atoms on surface using STM with electron spin resonance (ESR), nuclear magnetic resonance (NMR) in a high-field regime, where nuclear spins are expected to have long lifetimes, have been elusive. In addition, time-resolved measurements for the relevant timescales have not been reported.

In this talk, I will present our recent work on the nuclear spin of 47Ti and 49Ti atom (S = 1/2; I = 5/2 and 7/2) adsorbed on MgO/Ag using ESR-STM. First, we achieved single-shot readout of the nuclear spin of 49Ti. We apply radio-frequency (RF) pulses that drive ESR only if the nuclear spin is in a certain state (e.g., mI = –7/2), and then measure the DC tunneling conductance to probe whether ESR is driven or not. This new approach enables time-resolved measurements of the nuclear spin state, revealing its lifetime in the order of seconds – seven orders of magnitude longer than the electronic spin in the same atom. In addition, 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, through a flip-flop interaction between the nuclear and electron spins. Furthermore, we drove the NMR transitions in 47Ti isotopes with electron nuclear double resonance in a high field up to 1.4 T. As our work opens the door for further exploration of nuclear spins in on-surface atoms, I will also discuss the future directions and outlook의 강연을 진행하여 뜻 깊은 시간이 되었습니다.