Date and Time:  20-April-2023  3:30pm

Speaker:  Dr. Likun Wang, ICFO, Spain

Host: Kai Chang (BAQIS） 

Title:  Single Molecule Coherence with Femtosecond THz-STM

Abstract: 

A scanning tunneling microscope (STM) combined with femtosecond terahertz (THz) laser pulses can enable coherence measurements of single molecules. We report THz pump-probe measurements that demonstrate quantum sensing based on a hydrogen (H₂) molecule in the junction created with an STM tip near a surface. Atomic-scale spatial and femtosecond temporal resolutions were obtained from this quantum coherence. The H₂ acts as a two-level system (TLS) in a double-well potential, with its coherent oscillatory superposition exhibiting extreme sensitivity to the applied electric field and the underlying atomic composition and electrostatics of the copper nitride (Cu2N) monolayer islands grown on a Cu(100) surface. We acquired a series of time-lapsed images of THz induced rectification current of H₂ over Cu₂N islands for variable pump-probe delay times to visualize the heterogeneity of the chemical environment at sub-angstrom scale.

About the Speaker:

Likun Wang, a postdoctoral fellow at ICFO Spain, graduated from the Department of Physics at the University of California, Irvine in 2022, and is currently in. The main research direction is to combine low-temperature scanning tunneling microscopy (STM) with femtosecond pulsed laser (near-infrared/terahertz) to detect and regulate the quantum coherence of surface-adsorbed single molecules and single atoms.