The evolution and revival structure of angular momentum quantum wave packets (Tutorial)

In this paper a coherent superposition of angular momentum states created by absorption of polarized light by molecules is analyzed. Attention is paid to the time evolution of wave packets representing spatial orientation of internuclear axis of diatomic molecule. Two examples are considered in detail. Molecules absorbing light in a permanent magnetic field experiencing Zeeman effect and molecules absorbing light in a permanent electric field experiencing quadratic Stark effect. In a magnetic field we have a wave packet that evolves in time exactly as classical dipole oscillator in a permanent magnetic field. In the second case we have the wave packet that goes through periodical changes of a shape of the packet and revivals of initial shape. This is a pure quantum behavior. Classical motion of angular momentum in an electric field in case of quadratic Stark effect is known to be aperiodic. Obtained solutions for wave packet evolution are briefly compared with Rydberg state coherent wave packets and harmonic oscillator wave packets.