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International Journal of Quantum Information

EXPERIMENTAL ANALYSIS OF A SIMPLE LINEAR OPTICS PHASE GATE

Ch. Schmid, Nikolai Kiesel, Ulrich Weber, Rupert Ursin, Harald Weinfurter

Published Feb 1, 2007• 2 citations
Publisher

Abstract

Linear optics two-qubit logic gates are essential tools in photonic quantum information. We describe a recently introduced simple conditional phase gate for photons, which relies on only one second order interference at a polarization dependent beam splitter, thereby making additional stability precautions dispensable. The improved quality of the gate is evaluated by performing full process tomography. The obtained process tomography data is fitted by a model based on experimental parameters of the setup which allows predictions on the performance of the gate in multi-photon experiments. .

DOI
10.1142/s0219749907002682

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We report the first experimental demonstration of an optical quantum controlled-NOT gate without any path interference, where the two interacting path interferometers of the original proposals have been replaced by three partially polarizing beam splitters with suitable polarization dependent transmittance and reflectance. The performance of the device is evaluated using a recently proposed method, by which the quantum process fidelity and the entanglement capability can be estimated from the 32 measurement results of two classical truth tables, significantly less than the 256 measurement results required for full quantum tomography.
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We report on the usage of a linear optics phase gate for distinguishing all four Bell states simultaneously in a quantum teleportation and entanglement swapping protocol. This is demonstrated by full state tomography of the one and two qubit output states of the two protocols, yielding average state fidelities of about 0.83 and 0.77, respectively. In addition, the performance of the teleportation channel is characterised by quantum process tomography. The non classical properties of the entanglement swapping output states are further confirmed by the violation of a CHSH-type Bell inequality of 2.14 on average.
We report on the usage of a linear optics phase gate for distinguishing all four Bell states simultaneously in a quantum teleportation and entanglement swapping protocol. This is demonstrated by full-state tomography of the one- and two-qubit output states of the two protocols, yielding average state fidelities of about 0.83 and 0.77, respectively. In addition, the performance of the teleportation channel is characterized by the quantum process tomography. The non-classical properties of the entanglement swapping output states are further confirmed by the violation of a CHSH-type Bell inequality of 2.14 on average.