Experimental Verification of Decoherence-Free Subspaces

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Science  20 Oct 2000:
Vol. 290, Issue 5491, pp. 498-501
DOI: 10.1126/science.290.5491.498

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Using spontaneous parametric down-conversion, we produce polarization-entangled states of two photons and characterize them using two-photon tomography to measure the density matrix. A controllable decoherence is imposed on the states by passing the photons through thick, adjustable birefringent elements. When the system is subject to collective decoherence, one particular entangled state is seen to be decoherence-free, as predicted by theory. Such decoherence-free systems may have an important role for the future of quantum computation and information processing.

  • * To whom correspondence should be addressed. E-mail: kwiat{at}

  • Present address: Physics Department, California Institute of Technology, Pasadena, CA 91125, USA.

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