Quantum teleportation with pair-coherent states

Recently it has been argued that all presently performed continuous variable quantum teleportation experiments could be explained using a local hidden variable theory. In this paper we study a modification of the original protocol which requires a fully quantum mechanical explanation even when coherent states are teleported. Our calculations of the fidelity of teleportation using a pair-coherent state under ideal conditions suggests that fidelity above the required limit of 1/2 may be achievable in an experiment also.Comment: Based on talks at the QIP workshop in 6th Joint Conference on Mathematics and Computer Science, Pecs, 12-15 July 2006; and Quantum 2006 - Workshop ad memoriam Carlo Novero, Turin. v2: Added reference to give credit to L. Vaidma

Extreme sub-wavelength atom localization via coherent population trapping

We demonstrate an atom localization scheme based on monitoring of the atomic coherences. We consider atomic transitions in a Lambda configuration where the control field is a standing wave field. The probe field and the control field produce coherence between the two ground states. We show that this coherence has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of the atomic coherence would localize the atom. Interestingly enough the role of the cavity finesse is played by the ratio of the intensities of the pump and probe. This is in fact the reason for obtaining extreme subwavelenth localization. We suggest several methods to monitor the produced localization.Comment: 6 pages, 5 figure