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Q: Quantenoptik und Photonik

Q 45: Quanteninformation IV

Q 45.6: Talk

Friday, March 26, 2004, 12:30–12:45, HS 101

Continuous-variable experiments with a nonlocal single photon — •Sergei Babitchev, Jürgen Appel, and Alexander I. Lvovsky — Fachbereich Physik M559, Universität Konstanz

A dual-mode optical qubit, created by overlapping a single photon from a parametric down-conversion source and a vacuum mode on a beam splitter, is characterized by means of homodyne tomography. The reconstructed four-dimensional density matrix extends over the entire Hilbert space and thus reveals, for the first time, complete information about the qubit as a state of the electromagnetic state. A nonlocal character of the reconstructed ensemble is demonstrated by a violation of the Bell inequality for the quadrature data converted to a dichotomic format.

A remote preparation scheme of an arbitrary single-mode qubit has been implemented: a quadrature measurement, performed on one of the spatial modes of the nonlocal single-photon state, collapses it into a superposition of the single photon and the vacuum state in the other mode. Experimental results show that the preparation efficiency of the created qubit can be higher than that of the initial single photon.