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 on an insulator-metal surface arise from the superposition of its two-level quantum states that sensitively depend on its environment. Combining a sub-picosecond terahertz laser with a low temperature scanning tunneling microscope (STM), we present a comprehensive study of the coherence of a hydrogen molecule as it probes point defects in Cu<sub>2</sub>N/Cu(100) with simultaneous spatial and temporal resolutions . The interactions of the hydrogen molecule vary for different types of point defects as determined from variations in the frequency 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 and reveals hybridized orbitals surrounding the defects. These results validate supremacy of quantum sensing based on the coherent properties of single molecules that should be widely applicable to other chemical systems.

Single molecule coherence for sensing point defects with sub-picosecond and sub-nanometer resolutions within the STM cavity

ACS Spring 2022

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