Tracking spin flip-flop dynamics of surface molecules with quantum dissipation theory

The integration of scanning tunneling microscopy (STM) and electron spin resonance spectroscopy with voltage pulses is an emerging technique to probe the local spin dynamics of surface-adsorbed molecules. However, in experiments, the detection of real-time spin dynamics is severely hampered by the limited temporal resolution of STM electronics, and the associated theoretical investigations are still in their early stages due to various challenges in numerical simulations. In this work, we employ the highly accurate hierarchical equations of motion method to characterize the spin states and track the real-time coherent flip-flop spin dynamics in a surface-adsorbed hydrogenated Ti dimer. Our simulations accurately reproduce the experimental observations and reveal the influences of substrate and pulse duration on the spin decoherence process of the dimer. These achievements provide valuable insights into the coherent spin dynamics of surface-adsorbed molecules and set the stage for the application of surface-adsorbed molecular spins to quantum sensing, quantum information processing, and quantum computing.