The quantum coherence is considered within phase-sensitive nonadiabatic dressed states. Two types of phase correlations are found: a rapidly changing phase correlation between the real and the virtual components and a stationary phase correlation between different virtual components of these states.
The quantum coherence as a phase property of the most fundamental quantum mechanical entity, the wave function, is explained for the first time. Phase-sensitive nonadiabatic dressed states, arising from the interaction of a quantum system and a coherent external electromagnetic field, are used in these considerations. Two types of phase correlations in the multilevel phase-sensitive nonadiabatic dressed states are found: a rapidly changing phase correlation between the real and the virtual components and a stationary phase correlation between different virtual components of these states.
Abstract We theoretically investigate quantum virtual path interference caused by the dynamic Stark effect in bound–bound electronic transitions. The effect is studied in an intermediate resonant region and in connection with the energetic electron impact excitation of a helium atom embedded in a weak low-frequency laser field. The process under investigation is dealt with via a Born–Floquet approach. Numerical calculations show a resonant feature in laser-assisted cross sections. The latter is found to be sensitive to the intensity of the laser field dressing. We show that this feature is a signature of quantum beats which result from the coherent mixture of different quantum virtual pathways, and that excitation may follow in order to end up with a common final channel. This mixture arises from the dynamic Stark effect, which produces a set of avoided crossings in laser-dressed states. The effect allows one to coherently control quantum virtual path interference by varying the intensity of the laser field dressing. Our findings suggest that the combination of an energetic electron and a weak laser field is a useful tool for the coherent control of nonadiabatic transitions in an intermediate resonant region.
A modified Lang-Firsov transformation is used to study the exciton-phonon interaction in a two-site system embedded in a one-dimensional lattice. It describes an exciton partially dressed by a virtual phonon cloud and depends on a single variational parameter, the so-called dressing fraction, whose optimization is achieved by using both the standard Bogoliubov inequality and its improved version defined by Decoster [J. Phys. A 37, 9051 (2004)]. The optimization procedure is applied to build a phase diagram in the parameter space which defines the different states of the exciton depending on the adiabaticity, the coupling strength, and the temperature. It is shown that the two Bogoliubov inequalities yield different variational principles that give rise to two optimal dressing fractions. Special attention is thus paid to characterize their differences in the nonadiabatic limit, where the exciton evolves continuously from a partially dressed state in the weak-coupling limit to a fully dressed state in the strong-coupling limit, and in the adiabatic limit where a self-trapped transition takes place.
Nonadiabatic dressed states of a quantum system interacting with an external electromagnetic field and the environment are presented. The electromagnetic field is described in terms of carrier‐envelope concept. The amplitude and phase of the field are arbitrary functions of time, subject to a generalized adiabatic condition. The interaction with the environment is described my means of a dumping term in the Hamiltonian. The field time derivatives and the dumping play role of nonadiabatic factors. The main matrix elements within the nonadiabatic dressed states are found. A theory of quantum transitions based on the nonadiabatic dressed states is proposed for the first time.