title: Measuring a photonic qubit without destroying it.
abstract: 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.
authors.affiliation: Centre for Quantum Computer Technology, Department of Physics, University of Queensland, Brisbane 4072, Australia.
authors.forename: G J
authors.initials: GJ
authors.lastname: Pryde
authors.forename: J L
authors.initials: JL
authors.lastname: O'Brien
authors.forename: A G
authors.initials: AG
authors.lastname: White
authors.forename: S D
authors.initials: SD
authors.lastname: Bartlett
authors.forename: T C
authors.initials: TC
authors.lastname: Ralph