Frontiers of quantum physics

Abstract:

We present a rare example of a decay mechanism playing a constructive role in quantum information processing. We show how the state of an atom trapped in a cavity can be teleported to a second atom trapped in a distant cavity by the joint detection of photon leakage from the cavities. The scheme, which is probabilistic, requires only a single three level atom in a cavity. We also show how this scheme can be modified to a teleportation with insurance.

Abstract:

The natural thermal entanglement in an Ising ring in an external magnetic field was studied. The interactions of two qubits via the Ising interaction in a magnetic field orthogonal to the z direction was analyzed. A theorem for the concurrence mixing due to occupation of the ground and the excited state was formulated. The variation of entanglement with the orientation of magnetic field was numerically considered.

Abstract:

By considering quantum computation as a communication process, we relate its efficiency to its classical communication capacity. This formalism allows us to derive lower bounds on the complexity of search algorithms in the most general context. It enables us to link the mixedness of a quantum computer to its efficiency and also allows us to derive the critical level of mixedness beyond which there is no quantum advantage in computation.