ar X iv : q ua nt - p h / 05 09 14 6 v 1 2 1 Se p 20 05 Engineering atom - atom thermal entanglement via two - photon process

ar X iv : q ua nt - p h / 05 06 09 5 v 1 1 3 Ju n 20 05 Schmidt states and positivity of linear maps

Using pure entangled Schmidt states, we show that m-positivity of a map is bounded by the ranks of its negative Kraus matrices. We also give an algebraic condition for a map to be m-positive. We interpret these results in the context of positive maps as entanglement witnesses, and find that only 1-positive maps are needed for testing entanglement.

ua nt - p h / 05 09 21 8 v 1 3 0 Se p 20 05 N - qubit entanglement via the J 2 y - type collective interaction

ar X iv : q ua nt - p h / 05 09 08 5 v 1 1 3 Se p 20 05 Improving the purity of one - and two - qubit gates by AC fields

We investigate the influence of AC driving fields on the coherence properties of one-and two-qubit gate operations. In both cases, we find that for suitable driving parameters, the gate purity improves significantly. A mapping of the time-dependent system-bath model to an effective static model provides analytical results. The resulting purity loss compares favorably with numerical results.

ar X iv : q ua nt - p h / 05 09 19 4 v 1 2 8 Se p 20 05 Nonlocality without inequalities ∗

We prove that every conceivable hidden variable model reproducing the quantum mechanical predictions of almost any entangled state must necessarily violate Bell’s locality condition. The proof does not involve the consideration of any Bell inequality but it rests on simple set theoretic arguments and it works for almost any noncompletely factorizable state vector associated to any number of par...

ar X iv : q ua nt - p h / 01 11 11 0 v 1 2 1 N ov 2 00 1 Generating and probing a two - photon Fock state with a single atom in a cavity

A two-photon Fock state is prepared in a cavity sustaining a " source mode " and a " target mode " , with a single circular Rydberg atom. In a third-order Raman process, the atom emits a photon in the target while scattering one photon from the source into the target. The final two-photon state is probed by measuring by Ramsey interferometry the cavity light shifts induced by the target field o...