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Universal unitary gate for single-photon 2-qubit states

Berthold-Georg Englert·Christian Kurtsiefer·Harald Weinfurter
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Abstract

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.

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Berthold-Georg Englert, Christian Kurtsiefer, Harald Weinfurter. 2001-01-16. Universal unitary gate for single-photon 2-qubit states. https://doi.org/10.1103/physreva.63.032303

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