Quantum Boosts and Quantum Beats

Abstract

Quantum interference can occur in the time domain when a system evolves from an initial to a final energy state by more than one transition pathway. One way to accomplish this is to excite an atom into a linear superposition of close-lying Rydberg states by means of a broadband laser pulse. The author examines both weak and strong optical pumping with both short and long pulse widths. Strong optical pulses give rise to surprising nonlinear effects involving multiple absorptions and emissions during the pulse excitation. One such effect, engendered by a long strong pulse, is the restitution of quantum beats “washed out” by a long weak pulse. The occurrence of quantum beats in weak, moderate, and strong magnetic fields is also examined. A remarkable effect, predicted by the author, is that of “long-distance” quantum beats involving the radiative decay of entangled states of two identical, but widely separated, excited atoms. The example is of particular interest because quantum interference occurs even though each individual atom is not prepared in a linear superposition of excited states.