A. Kozhekin

Control of non-Markovian decay and decoherence by measurements and interference

Novel methods are discussed for the state control of atoms coupled to multi-mode reservoirs with non-Markovian spectra: 1) Excitation decay control : we point out that the quantum Zeno effect, i.e., inhibition of spontaneous decay by frequent measurements, is observable in open cavities and waveguides using a sequence of evolution- interrupting pulses or randomly-modulated CW fields. 2) Location-dependent interference of decay channels - nonadiabatic (resonant) control : We show that the control of populations and coherences of two metastable states is feasible via resonant single-photon absorption to an intermediate state, by controlled spontaneous emission in a cavity. 3) Decoherence control by conditionally interfering parallel evolutions: We demonstrate that an arbitrary internal atomic state can be completely protected from decoherence by interference of its interactions with the reservoir over many different time interals in parallel . Such interference is conditional upon the detection of appropriate atomic-momentum observables. Realization in cavities is suggested. The rich arsenal of control methods described above can improve the performance of single-atom devices. It can also advance the state-of-the-art of quantum information encoding and processing.

Superluminal pulse transmission through a phase-conjugating mirror.

Abstract We theoretically analyze wave packet transmission through a phase-conjugating mirror and show that the transmission of a suitably chosen input pulse is superluminal, i.e. the peak of the pulse emerges from the mirror before the time it takes to travel the same distance in vacuum. This pulse reshaping effect can be attributed directly to the dispersion relation in the nonlinear medium constituting the mirror. Thus, for the first time a connection is laid between optical phase conjugation and superluminal behavior. In view of its additional amplifying ability, a phase-conjugating mirror is a most promising candidate for an experimental observation of tachyonic signatures.

Cooperative and Coherent Optical Processes in Field Confining Structures

We survey our recent results on the modifications of optical processes by field confining structures

Tachyonic information transfer in parametric amplifiers

The injection of spectrally narrow probe wavepackets into quantized parametrically amplifying media can give rise to transient tachyonic wavepackets. Remarkably, their quantum information, albeit causal, is confined to times corresponding to superluminal velocities, which is advantageous for communications.