Quantum Memory for Photons in Case of Many Close Lying Exciton Resonances in Solids

The possibility of storage of quantum information with photons is studied in the case of resonant transitions via many close lying exciton levels in a solid with impurity Lambda-atoms. The upper levels of the impurity atom form resonant Fano states, similar to the autoionization atomic states, due to the configuration interaction with the continuum of the exciton band. In this case slowing of light pulses is shown to be realistic, in the presence of the control field, down to the group velocity much lower than that in vacuum. The possibility of storage and reconstruction of a quantum pulse is studied in the case of the instantaneous switching on/off of the control field. It is shown that the signal quantum pulse cannot be stored undistorted for differing values of Fano parameters and for non-zero two-photon detuning and decay rate between the lower levels (decoherence). However, for small difference of the Fano parameters and for small values of the two-photon detuning and the decoherence there is no distortion in the case where the length of the pulse is much longer than the linear absorption (amplification) length, so the shape and quantum state of the light pulse can be restored.Comment: 15 pages, 3 figure

Pulse propagation, population transfer and light storage in five-level media

We consider adiabatic interaction of five-level atomic systems and their media with four short laser pulses under the condition of all two-photon detunings being zero. We derive analytical expressions for eigenvalues of the system's Hamiltonian and determine conditions of adiabaticity for both the atom and the medium. We analyse, in detail, the system's behaviour when the eigenvalue with non-vanishing energy is realized. As distinct from the usual dark state of a five-level system (corresponding to zero eigenvalue), which is a superposition of three states, in our case the superposition of four states does work. This seemingly unfavourable case is nevertheless demonstrated to imitate completely a three-level system not only for a single atom but also in the medium, since the propagation equations are also split into those for three- and two-level media separately. We show that, under certain conditions, all the coherent effects observed in three-level media, such as population transfer, light slowing, light storage, and so on, may efficiently be realized in five-level media. This has an important advantage that the light storage can be performed twice in the same medium, i.e., the second pulse can be stored without retrieving the first one, and then the two pulses can be retrieved in any desired sequence

Implementation of a double-scanning technique for studies of the Hanle effect in Rubidium vapor

We have studied the resonance fluorescence of a room-temperature rubidium vapor exited to the atomic 5P3/2 state (D2 line) by powerful single-frequency cw laser radiation (1.25 W/cm^2) in the presence of a magnetic field. In these studies, the slow, linear scanning of the laser frequency across the hyperfine transitions of the D2 line is combined with a fast linear scanning of the applied magnetic field, which allows us to record frequency-dependent Hanle resonances from all the groups of hyperfine transitions including V- and Lambda - type systems. Rate equations were used to simulate fluorescence signals for 85Rb due to circularly polarized exciting laser radiation with different mean frequency values and laser intensity values. The simulation show a dependance of the fluorescence on the magnetic field. The Doppler effect was taken into account by averaging the calculated signals over different velocity groups. Theoretical calculations give a width of the signal peak in good agreement with experiment

Coherent control of interference processes in radiative decays

Possibility of coherent control of spontaneous emission from four- and five-level system in the laser radiation field is studied. The four-level system consists of two levels resonantly driven by laser radiation where either of levels may decay to a separate level. For such a system, we show that the presence of the second decay channel may deteriorate the destructive interference occurring in case of one decay channel because of Autler-Townes effect. The five-level diagram represents two two-level resonantly driven systems with the upper levels decaying to a common level. For this diagram, interference between the two decay channels takes place and it is partially or completely destructive or constructive depending on the initial conditions and on the mutual orientation of the transition dipole moments. It is shown that population transfer takes place by the same quantum vacuum via spontaneous emission. The populations are shown to have damping oscillatory nature