Single molecule coherence for sensing point defects with space-time resolution within the STM Cavity

The quantum coherence of a single molecule can have extreme sensitively on its environment and thus provide unmatched precision in measurements. Here, we demonstrate that the coherent oscillations of a hydrogen molecule adsorbed on a surface arise from the superposition of its two-level quantum states that sensitively depend on its environment. Combining a femtosecond terahertz laser with a low temperature scanning tunneling microscope, we present a comprehensive study of the coherence of a hydrogen molecule as it probes point defects in Cu₂N islands grown on Cu(100) with simultaneous spatial and temporal resolutions . Single hydrogen molecules serve as quantum sensors of different types of point defects and surface heterogeneity as determined from variations in the frequency, phase and de-coherence time of the coherent oscillations. Time resolved imaging of the molecular coherence provides a movie of the changes in space and time. The extreme position sensitivity of the phase and frequency reveals a spatially varying local potential surrounding the defects. These results validate the supremacy of quantum sensing based on the coherent properties of single molecules that should be widely applicable to other nanoscale systems.