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arXiv:0711.4534 · Physical Review Letters

Experimental Realization of Linear-Optical Partial swap Gates

Antonín Černoch, Jan Soubusta, Lucie Bartůšková, Miloslav Dušek, Jaromı́r Fiurášek

Published May 6, 2008• 47 citations
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Abstract

We present a linear-optical implementation of a class of two-qubit partial SWAP gates for polarization states of photons. Different gate operations, including the SWAP and entangling sqrt[SWAP], can be obtained by changing a classical control parameter, namely, the path difference in the interferometer. Reconstruction of output states, full quantum process tomography, and an evaluation of entanglement of formation prove very good performance of the gates.

DOI
10.1103/physrevlett.100.180501

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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 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.
We present a linear optical scheme for the implementation of a three-qubit quantum gate that can be considered as a generalization of the two-qubit partial-SWAP gate. The gate leaves unchanged all fully symmetric states of three qubits, and all states antisymmetric with respect to the transposition of some pair of qubits acquire a phase shift $\ensuremath{\phi}$. The gate operates in the coincidence basis and requires one auxiliary pair of photons prepared in the maximally entangled Bell state. By altering parameters of the proposed interferometric scheme, we can also obtain a quantum filter that attenuates amplitudes of the three-qubit states according to their permutation symmetry properties.
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.