Quantum sensing base on the conformational transitions of single molecules

Advances in quantum sensors, including spin , charge , and flux qubits have demonstrated advantages in sensitivity and precision. Here, we realized a quantum sensing microscope based on transitions between different conformational states of a single adsorbed pyrrolidine in the STM junction. The conformational transitions can be induced by tunneling electrons or by light. The transition rate, population, and lifetime of the conformational states of a single pyrrolidine molecule attached to the apex of a STM tip showed subatomic scale variations over different lateral positions of a single layer of copper nitride (Cu₂N) surface. For a bare tip, these conformational transition statistics for an adsorbed pyrrolidine molecule showed a nearly isotropic spatial distribution on the Cu(001) surface, a two-fold symmetric pattern on the Cu₂N surface, and sensitive coupling to an adjacent coadsorbed pyrrolidine molecule on Cu(001). Our results demonstrated the sensitivity of a two-level system based on molecular conformation states for quantum sensing of soft and solid surfaces. The fact that the transitions were differently induced by electrons and light provided a pathway for controlling the states of the molecular qubits.