Phys. Rev. Lett. 92, 107901 (2004) [4 pages]Decoherence-Free Quantum Information Processing with Four-Photon Entangled StatesReceived 22 August 2003; published 9 March 2004 Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only. © 2004 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.92.107901
DOI:
10.1103/PhysRevLett.92.107901
PACS:
03.67.Pp, 03.65.Yz, 03.67.Hk, 42.65.Lm
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