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Phys Rev Lett. 2004 May 14;92(19):190402. Epub 2004 May 12.

Measuring a photonic qubit without destroying it.

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Centre for Quantum Computer Technology, Department of Physics, University of Queensland, Brisbane 4072, Australia.


Measuring the polarization of a single photon typically results in its destruction. We propose, demonstrate, and completely characterize a quantum nondemolition (QND) scheme for realizing such a measurement nondestructively. This scheme uses only linear optics and photodetection of ancillary modes to induce a strong nonlinearity at the single-photon level, nondeterministically. We vary this QND measurement continuously into the weak regime and use it to perform a nondestructive test of complementarity in quantum mechanics. Our scheme realizes the most advanced general measurement of a qubit to date: it is nondestructive, can be made in any basis, and with arbitrary strength.

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