Indistinguishability and Interference in the Coherent Control of Atomic and Molecular Processes

TL;DR

This paper explores how quantum indistinguishability and entanglement influence coherent control of atomic and molecular processes, emphasizing the role of light states and the limits of coherence transfer.

Contribution

It demonstrates that coherence transfer from classical light states enables phase control, while quantum light states can reduce control due to which-way information leakage.

Findings

Coherence transfer from classical light states facilitates phase control.

Quantum light states can suppress phase-sensitive control.

Incoherent interference control ensures pathway indistinguishability.

Abstract

The subtle and fundamental issue of indistinguishability and interference between independent pathways to the same target state is examined in the context of coherent control of atomic and molecular processes, with emphasis placed on possible "which-way" information due to quantum entanglement established in the quantum dynamics. Because quantum interference between independent pathways to the same target state occurs only when the independent pathways are indistinguishable, it is first shown that creating useful coherence (as defined in the paper) between nondegenerate states of a molecule for subsequent quantum interference manipulation cannot be achieved by collisions between atoms or molecules that are prepared in momentum and energy eigenstates. Coherence can, however, be transferred from light fields to atoms or molecules. Using a particular coherent control scenario, it is shown that this coherence transfer and the subsequent coherent phase control can be readily realized by the most classical states of light, i.e., coherent states of light. It is further demonstrated that quantum states of light may suppress the extent of phase-sensitive coherent control by leaking out some which-way information while "incoherent interference control" scenarios proposed in the literature have automatically ensured the indistinguishability of multiple excitation pathways. The possibility of quantum coherence in photodissociation product states is also understood in terms of the disentanglement between photodissociation fragments. Results offer deeper insights into quantum coherence generation in atomic and molecular processes.