The STIRAP-based unitary decelerating and accelerating processes of a single free atom

A STIRAP-based unitary decelerating (accelerating) process consists of a train of the standard three-state STIRAP pulse sequences which may act as the basic unitary decelerating (accelerating) sequences. The present work is focused on investigating analytically and quantitatively how the momentum distribution of a momentum superposition state such as a momentum Gaussian wave-packet state of a single freely moving atom affects the STIRAP state transfer in these decelerating and accelerating processes. The complete STIRAP state transfer and the unitarity of these processes are stressed highly in the investigation. It has been shown that the momentum distribution has an important influence upon the STIRAP state-transfer efficiency. In the ideal adiabatic condition these unitary decelerating and accelerating processes for a freely moving atom are studied in detail, and it is shown that they can be used to manipulate and control in time and space the center-of-mass position and momentum of a Gaussian wave-packet motional state of a free atom. Two general (strict and accurate) adiabatic conditions for the basic STIRAP decelerating and accelerating processes are derived analytically. With the help of the STIRAP theory and the unitary quantum dynamics it confirms theoretically that the time- and space-compressing processes of the quantum control process (quant-ph/0607144) can be realized almost perfectly by the STIRAP-based unitary decelerating and accelerating processes in the ideal or nearly ideal adiabatic condition.