Quantum Stochastic Rectification in a Single Molecule.

Quantum stochastic rectification arises from the dc response of a system subjected to both quantum noise and a small, periodic sinusoidal voltage modulation. In this Letter, we demonstrate quantum stochastic rectification by using inelastic electron tunneling spectroscopy with a scanning tunneling microscope to monitor the conformational switching of a single pyrrolidine molecule adsorbed on a Cu(001) surface. By applying quasistatic and nonequilibrium approximations, we elucidate the underlying dynamic response mechanisms. Additionally, we establish a quantitative relationship between the critical driving frequency in rectification measurements and the system's relaxation time, facilitating the measurement of rapid relaxation rates in single molecules.