Upon entangling a spatial binary alternative of a photon with its polarization, one can use single photons to study arbitrary 2-qubit states. Sending the photon through a Mach-Zehnder interferometer, equipped with sets of wave plates that change the polarization, amounts to performing a unitary transformation on the 2-qubit state. We show that any desired unitary gate can be realized by a judicious choice of the parameters of the set-up and discuss a number of applications. They include the diagnosis of an unknown 2-qubit state, an optical Grover search, and the realization of a thought experiment invented by Vaidman, Aharonov, and Albert.
@article{arxiv.quant-ph/0101064,
title = {Universal unitary gate for single-photon 2-qubit states},
author = {Berthold-Georg Englert and Christian Kurtsiefer and Harald Weinfurter},
journal= {arXiv preprint arXiv:quant-ph/0101064},
year = {2009}
}
Comments
to appear in Phys. Rev. A, 10 pages, 7 figures, 2 tables