Onset of decoherence:Six-wave mixing measurements of vibrational decoherence on the excited electronic state of I_2 in solid argon

摘要

Pump-probe,four-wave,and six-wave mixing measurements of I_2 isolated in solid argon are used to provide a clear experimental measure for the onset of vibrational quantum decoherence on the excited electronic state.The electronically resonant,six-wave mixing measurements bypass the rapid electronic dephasing,and measure the quantum cross-correlation between two packets launched on the B-state.The vibrational quantum coherence survives one period of motion,400 fs,during which -2000 cm~-1 of energy is transferred to the lattice.The decoherence occurs during the second cycle of motion,while classically coherent motion measured via pump-probe spectroscopy using the same electronic resonances continues for -15 periods.This is contrasted with vibrational dephasing on the ground electronic surface,which lasts for 10~2 periods,as measured through time-resolved coherent anti-Stokes Raman scattering.The measurements and observables are discussed through time-circuit diagrams,and a mechanistic description of decoherence is derived through semiclassical analysis and simulations that reproduce the experiments.