308 / 2019-02-23 05:12:11

Coherent control of electron-phonon coupled states in GaAs using relative-phase-locked femtosecond optical pulses

coherent control

全体主题 > Fundamental Physics at Extremes

Coherence is a key source for the future quantum information and device technologies. Although the quantum coherence is kept in an isolated system, it is easily lost in a condensed matter due to the strong interaction with its environment and hard to be detected. Here we developed a new technique to measure the coherent time in the electron-phonon coupled states in solid materials by via the time-domain interferometry using relative-phase-locked femtosecond laser pulses.
We performed a double-pump and probe protocol for transient reflectivity measurement in n-type GaAs with (100) surface at 90 K. The pump pulses were relative phase-locked femtosecond pulses [1] with a pulse width of approximately 60 fs and a center wavelength of 800 nm. The energy of the light was above the bandgap. The double-pump pulses were characterized with a fringe-resolved autocorrelation technique. The longitudinal optical (LO) phonon (8.8 THz) and LO phonon-plasmon coupled mode oscillation (LOPC, 7.8 THz) were coherently excited by a pump pulse and their oscillations were detected by the transient reflectivity of the probe pulse [2]. In the double pulse excitation, the phonon states excited by each pulse interferes each other and the LO phonon amplitude is modulated as a function of the pump-pump delay (t12). This is the time-domain interferometry between the electron-phonon coupled states, and the result corresponds to the coherent control. The coherent phonons are generated through transition to the electronic excited state [2]. The pump-pump-delay dependence showed fringes with intervals of approximately 2.7 fs and 116 fs due to the electronic and phonon coherence, respectively. The electronic coherence is preserved until approximately 120 fs after the end of overlapping the pump pulses. The fringe amplitude of the electronic coherence showed an apparent collapse and revival feature, which is explained via a quantum-path interference between the transition paths for generation the coherent phonons with a help of quantum mechanical calculations.