High-Precision Coherent Control of Molecular Wave Packets

The quantum interference of two vibrational wave packets has been precisely controlled in the electronically excited state of a diatomic molecule by using a pair of fs laser pulses whose relative phase $\phi $ is locked within the attosecond time scale, and the real time evolution of that interference has been observed by another fs probe pulse. The real-time evolution shows a clear dependence on $\phi $. We have also measured a population code, which is a population ratio among the vibrational eigenstates within a WP. The population code also shows a clear dependence on $\phi $. The ordinary frequency domain interpretation based on the spectral interference of locked pulses may be useful to elucidate $\phi $ dependence of population codes, but is no longer suitable for the present real-time observation. The combination of a population code and real-time evolution is useful to obtain both phase and amplitude information stored in a WP.