Coherent phenomena in multilevel systems with closed interaction contour

Abstract

The work presented considers a new coherent phenomenon, i.e. the influence of the phases of electromagnetic fields interacting with a multilevel system on the character of excitation of this system. On the basis of analysing the equation for an N-level quantum system density matrix, it was established that in multilevel systems containing a closed contour of transitions, resonantly interacting with the field, stationary populations always depend on the total interaction contour phase Phi . For the simplest multilevel systems, i.e. three-level, the authors have obtained analytical expressions, connecting populations with the relative field phase in such systems. Thus, for a Lambda system, interacting with three resonant electromagnetic fields, it is discovered that, depending on the total phase value of the transition contour, both destruction and successive restoration of a coherent trapping state can take place. The work provides qualitative explanations of phase effects and suggests some possibilities for their application.

Phase-dependent interaction in a four-level atomic configuration

“…In the absence of spontaneous decay, the ♦ configuration is formally identical to the double-Λ scheme, extensively studied in the literature [4,5,6]. Thus, the symmetries induced on the coherent dynamics by the phase are exactly the same [3].…”

“…This scheme has a closed-loop excitation structure [3,4], i.e. any transition amplitude between two given states is the sum of two contributions, corresponding to two excitation paths, which may interfere.…”

“…For the configuration we consider here there exists in general no reference frame in which this explicit time-dependence can be eliminated. This is a characteristic of "closed-loop" configurations [4], and it is a manifestation of the intrinsic phase sensitivity of the dynamics. However, in an adequate reference frame, the Rabi frequencies can be chosen such that only one is complex, with its phase Φ being a function of all laser phases.…”

“…This is no longer fulfilled in closed-loop configurations [3,4], i.e. when a set of atomic states is (quasi-) resonantly coupled by laser fields, such that each state of the set is connected to any other via two different paths of coherent photon-scattering: In this case, the relative phase Φ between the transitions determines the interference and hence critically influences the dynamics and steady state of the system [3,4,5].…”

Phase-dependent light propagation in atomic vapors

“…Recent studies have been focusing on the dynamics of light interacting with atoms featuring coupled energy levels in a so-called 'closed-loop' configuration [9,10]. In this configuration a set of atomic states is (quasi-) resonantly coupled by laser fields so that each state is connected to any other via two different paths of coherent photon-scattering.…”