Quantum Interference Visibility Spectroscopy in Two-Color Photoemission from Tungsten Needle Tips

When two-color femtosecond laser pulses interact with matter, electrons can be emitted through various multiphoton excitation pathways. Quantum interference between these pathways gives rise to a strong oscillation of the photoemitted electron current, experimentally characterized by its visibility. In this Letter, we demonstrate the two-color visibility spectroscopy of multiphoton photoemissions from a solid-state nanoemitter. We investigate the quantum pathway interference visibility over an almost octave-spanning wavelength range of the fundamental (omega) femtosecond laser pulses and their second harmonic (2 omega). The photoemissions show a high visibility of 90% +/- 5%, with a remarkably constant distribution. Furthermore, by varying the relative intensity ratio of the two colors, we find that we can vary the visibility between 0% and close to 100%. A simple but highly insightful theoretical model allows us to explain all observations, with excellent quantitative agreements. We expect this work to be universal to all kinds of photo-driven quantum interference, including quantum control in physics, chemistry, and quantum engineering.

Automated summary

By studying the two-color visibility spectroscopy of multiphoton photoemissions from a solid-state nanoemitter, it was found that the visibility was around 90%, which could be varied between 0% and close to 100% by adjusting the relative intensity ratio of the two colors. Additionally, a theoretical model was able to explain all observations with great quantitative agreements, indicating the universality of this work in photo-driven quantum interference in various fields.