# Ultrafast Quantum-path Interferometry Revealing the Generation Process of Coherent Phonons

## TL;DR

This paper demonstrates ultrafast quantum-path interferometry in n-GaAs, revealing that coherent phonons are generated via impulsive stimulated Raman scattering influenced by surface-charge fields, using phase-locked dual femtosecond pulses.

## Contribution

It introduces a novel interferometric method to observe quantum pathways of coherent phonon generation in bulk solids.

## Key findings

- Interference fringes observed in transient reflectivity measurements.
- Quantum-path interference confirmed through theoretical calculations.
- Coherent phonons generated via impulsive stimulated Raman scattering influenced by surface-charge fields.

## Abstract

Optical dual-pulse pumping actively creates quantum-mechanical superposition of the electronic and phononic states in a bulk solid. We here made transient reflectivity measurements in an n-GaAs using a pair of relative-phase-locked femtosecond pulses and found characteristic interference fringes. This is a result of quantum-path interference peculiar to the dual-pulse excitation as indicated by theoretical calculation. Our observation reveals that the pathway of coherent phonon generation in the n-GaAs is impulsive stimulated Raman scattering at the displaced potential due to the surface-charge field, even though the photon energy lies in the opaque region.