The quantum Zeno effect (QZE) is the striking possibility of  slowing down the decay of an unstable quantum state by sufficiently  frequent measurements. This effect had been believed to be universal. However, we have shown that more commonly frequent measurements can accelerate decay, causing the anti-Zeno effect (AZE). We have developed a unifying theory for the QZE and AZE. We have then generalized it to a universal strategy for the controlled slowdown of decay and decoherence by various frequent interventions, particularly laser pulses.  We are studying various experimental situations in which such decoherence control can protect quantum information: atomic radiative decay in cavities, photon depolarization, cold-atom tunneling, macroscopic tunneling in Josephson junctions, vibrational relaxation in ion traps or molecules. (Classified index, Abraham Kofman)

The use of quantum mechanics in information processing offers striking new possibilities: quantum cryptography and teleportation of quantum states, quantum logic whose coveted goal is quantum computing. The main resource are here the so called entangled states, revealing the most curious property of the quantum world, namely, nonlocality. As the quality of entanglement is decisive for quantum information, we have been developing methods for entanglement enhancement and protection from decoherence: deterministic (nearly 100% certain) quantum logic schemes based on the entanglement of two ultraslow photons, schemes for multi-atom entanglement in cold gases and solids. Translational (position and momentum) entanglement schemes based on quasimolecule dissociation and collisions have been pioneered by us. (Classified index)

Our interest is in trying to understand  how we can manipulate Bose-Einstein condensates (BECs) using light. Shining lasers onto a BEC can modify the interatomic potential  seen by the constituent atoms. By varying the intensity and frequency of the lasers one effectively has a 'knob' which allows one to continuously change the properties of the condensate. We are studying laser-induced long-range cold atom-atom scattering and translationally entangled (EPR) multi-atom states in optical lattices, i.e., periodic arrays of microscopic potentials created by a web of interfering laser beams. We have predicted that random occupancy of atomic sites and long-range atom-atom interactions in optical lattices can give rise to novel scattering transport and localization effects, akin to those of strongly disordered media. (Classified index)

Electronically excited species (molecules, atoms or excitons) undergo fundamental changes  when they are located in dielectric structures in which the refractive index varies strongly on a submicron scale. Drastic modifications of nonlinear and quantum optical processes, energy transfer and reactive collisions in these systems have been predicted by us in cavities, dielectric microspheres and novel 2d- or 3d-periodic gratings which exhibit forbidden spectral bands (photonic band gaps). We have discovered and studied novel types of optical solitons in structures with periodic modulation of the linear refractive index and thin layers of resonant atoms: bright and dark solitons in photonic band gaps, as well as "light bullets", i.e., multi-dimensional solitons that are localized in both space and time. (Classified index)

In an attempt to overcome the adverse effect of momentum spread on FEL gain, we have put forward new concept inspired by lasing without inversion (LWI) in atomic systems, namely, the cancellation of absorption by interference in the gain medium. The analogous schemes proposed by us for FELs involve two wigglers coupled by a specially designed drift region. Net gain is obtained in such schemes even from beams with a very broad (inhomogeneous) momentum spread, whence we named them FELs without inversion. We have recently proposed a considerably simpler variant of such schemes, aimed at extending the optical gain bandwidth in FELs. The proposed setup involves only optical (laser) phase shifts in the drift region. These phase shifts are much easier to manipulate, since they require only linear optical elements - prisms or Bragg mirrors, etc. The proposed scheme is universal, i.e., applicable to FELs regardless of their wiggler design. We conclude that interference-based schemes may substantially enhance the FEL performance in the pulsed regime. (Classified index)