Letters to Nature

Nature 410, 1067-1070 (26 April 2001) | doi:10.1038/35074041; Received 27 November 2000; Accepted 21 February 2001

Entanglement purification for quantum communication

Jian-Wei Pan, Christoph Simon1, S caronaslav Brukner & Anton Zeilinger

  1. Institut für Experimentalphysik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria
  2. Present address: Centre for Quantum Computation, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK.

Correspondence to: Anton Zeilinger Correspondence and requests for materials should be addressed to A.Z. (e-mail: Email: Zeilinger-office@exp.univie.ac.at).

The distribution of entangled states between distant locations will be essential for the future large-scale realization of quantum communication schemes such as quantum cryptography1, 2 and quantum teleportation3. Because of unavoidable noise in the quantum communication channel, the entanglement between two particles is more and more degraded the further they propagate. Entanglement purification4, 5, 6, 7 is thus essential to distil highly entangled states from less entangled ones. Existing general purification protocols4, 5, 6 are based on the quantum controlled-NOT (CNOT) or similar quantum logic operations, which are very difficult to implement experimentally. Present realizations of CNOT gates are much too imperfect to be useful for long-distance quantum communication8. Here we present a scheme for the entanglement purification of general mixed entangled states, which achieves 50 per cent of the success probability of schemes based on the CNOT operation, but requires only simple linear optical elements. Because the perfection of such elements is very high, the local operations necessary for purification can be performed with the required precision. Our procedure is within the reach of current technology, and should significantly simplify the implementation of long-distance quantum communication.