Andrzej Raczynski

We present the concept of a realization of three-photon interference based on the procedure of light storage and release. Three probe photons are stored in an atomic medium in the tetrapod configuration. The medium irradiated by three control fields is shown to act as a flexible tritter. By changing the control fields applied at three stages of the photons' release, one can regulate the probabilities of obtaining various numbers of photons at each stage. Some of the signal coincidence probabilities can be made equal to zero, which is a generalization of the Hong-Ou-Mandel effect. The interference is demonstrated to gradually disappear for an increasing degree of the photons' distinguishability.

The propagation, storage, and release of two quantized light fields in an optically dressed atomic medium in the tripod configuration are studied. Using the formalism of spinor dark-state polaritons, the probabilities are obtained of finding outgoing photons of two possible localizations and two possible types, i.e., having different frequencies or polarizations. An additional interaction at the storage stage is applied which modifies the atomic coherences due to the stored photons; this results in a modification of the states of the outgoing photons. The conditions are examined for the photons' spatial and type coalescence typical of the Hong-Ou-Mandel effect, i.e., a zero probability of finding the outgoing photons having not only different localizations but also types. These results can possibly be observed in rubidium vapors.

Pulse propagation is studied in an EIT medium with the control field having a periodically varying phase (chirp). Based both on numerical calculations and on an approximate approach neglecting absorption and nonadiabatic effects, it is shown that transparency occurs for probe pulses having a sufficiently narrow envelope and an appropriately suited chirp. For other chirped pulses the evolution of their spectra along a sample is studied. Using a projection method one can divide a pulse into a part for which the medium is transparent and a rest for which it is opaque.

A probe pulse propagation is examined in a medium irradiated by three control fields which constitute a triangular loop system being, in general, out of resonance. As a consequence, the probe field interacts with the medium dressed in a time-dependent way. Coupled equations for the Floquet components of the probe field are written and solved by diagonalizing the coupling matrix. Examples of numerical solutions are presented and discussed.

Simultaneous propagation of two probe pulses in a medium of four-level atoms irradiated by three control fields is studied. The double Λ configuration has been closed by a fifth field, coupling the lower levels. It is shown that the propagation can be described in terms of four modes characterized by particular effective susceptibilities, which have absorption or gain peaks and transparency windows. For incoming one-peak pulses, multipeak spectra are built during the propagation including a few components of well-defined frequencies. They evolve along the sample with some of their spectral components being transmitted, absorbed, or amplified.

Weak probe-pulse propagation is studied in a three-level atomic system irradiated by a strong control laser field and a strong microwave field in the closed-loop triangular (Δ) configuration. In addition to the direct absorption channel, a second channel is activated in which a probe photon’s absorption is replaced by its emission accompanied by an absorption of two control and two microwave photons. The pulse can be considered a superposition of two components, each of which experiences a separated effective susceptibility, exhibiting its absorption/gain windows. The evolution of the pulse spectrum in space and the pulse evolution in space–time are discussed. In particular it is shown that the number and positions of the spectrum peaks change and the pulse exhibits beats. In addition to the propagating field, a stationary light generated by the sample is also discussed.