Strong-field subcycle control of dissociation dynamics via exceptional points of molecules in an electric field

Quantum systems depending on parameters may have exceptional points (EPs) in the parameter space where complex energies of their resonance states coalesce. Here we show that electronic Siegert states of molecules in a static electric field have EPs in the internuclear distance-field strength plane. Given a molecule undergoing dissociation launched, e.g., by its photoionization, the EPs enable one to control the final state of the products by applying a strong low-frequency laser pulse. The possibility of such a control has a threshold dependence on the pulse intensity, which is the main signature of the EPs in observables. The control occurs on subcycle time scales and can be accomplished by few-cycle pulses of the type used in strong-field physics. We present a theory predicting and describing this mechanism and illustrate it by calculations for the process H-2+(2p sigma(u)) -> H(nl) + p.