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Entanglement and teleportation improvement by conditional measurement

- Two photon entanglement in doped Photonic Crystals. Giantly enhanced cross-phase modulation with suppressed spectral broadening is predicted between optically-induced dark-state polaritons whose propagation is strongly affected by photonic bandgaps of spatially periodic media with multilevel dopants. Partner 5 demonstrated that this mechanism is capable of fully entangling two single-photon pulses with high fidelity.

- Generation and Communication of Photon-Photon and Atom-Atom Entangled States. Partner 5 introduced two schemes for generation and transfer of photon-photon and atom-atom entanglement. A method was proposed to achieve a large conditional phase shift of a probe field in the presence of a single-photon control field. This scheme allows, in principle, high-fidelity state transfer from the entangled dissociated fragments to light, thereby producing a highly correlated photon pair.

- Towards High-Fidelity Two-Photon Quantum Communications. Two alternative schemes for highly efficient nonlinear interaction between weak optical fields were proposed by Partner 5. The first scheme is based on the attainment of electromagnetically induced transparency simultaneously for two fields via transitions between magnetically split F = 1 atomic sublevels, in the presence of two driving fields. The second scheme relies on simultaneous electromagnetically - and selfinduced transparencies of the two fields.

- Dynamical Control of Decay and Decoherence in Complex Quantum Systems.
-- The impediment towards the successful development of the field of quantum information (QI) is decoherence, i.e., the loss of entanglement by the effect of the environment on the systems of interest. An important challenge is that of QI engineering, by entanglement and decoherence control, in complex systems, such as unimolecular and bimolecular systems that can simultaneously handle large amounts of QI. Partner 5 gave a unified theory of dynamically modified decay and decoherence in driven quantum systems that are coupled to arbitrary finitetemperature reservoirs and undergo random phase fluctuations. Decay acceleration by frequent measurements (interruptions of the coupling), known as the anti-Zeno effect (AZE) was argued to be much more ubiquitous than its inhibition in one- or two-level systems coupled to reservoirs (continua). In multilevel systems, frequent measurements cause accelerated decay by destroying the multilevel interference, which tends to inhibit decay in the absence of measurements.

-- The realization of the position- and momentum-correlated atomic pairs that are confined to adjacent sites of two mutually shifted optical lattices and are entangled via laser-induced dipoledipole interactions was discussed by Partner 5. The Einstein-Podolsky-Rosen (EPR) paradox with translational variables is then modified by lattice-diffraction effects. This paradox can be verified to a high degree of accuracy in this scheme. A method for controlling the decoherence of a driven qubit which is strongly coupled to a reservoir, when the qubit resonance frequency is close to a continuum edge of the reservoir spectrum, was proposed. Partner 5 demonstrated that an appropriate sequence of nearly abrupt changes of the resonance frequency can protect the qubit state from decay and decoherence more effectively than the intuitively obvious alternative, which is to fix the resonance well within a forbidden bandgap of the reservoir spectrum, as far as possible from the continuum edge.

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