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Conference on Lasers and Electro-Optics

Quantum state tomography using photon number counting to evaluate entanglement generated by spontaneous parametric downconversion

Akio Yoshizawa, Daiji Fukuda, Hidemi Tsuchida

Published Jan 1, 2012• 0 citations
Publisher

Abstract

We analyze polarization-entangled photon pairs using detectors that can or cannot count photons to discuss accuracy of the fidelity estimated by quantum state tomography. The use of four photon-number-resolving detectors presents best accuracy.
DOI
10.1364/qels.2012.qf3f.2

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Entangled-photon pairs are essential for many applications in quantum computation and communication, and quantum state tomography (QST) is the universal tool to characterize such entangled-photon sources. In QST, very low-power signals must be measured with single-photon detectors and coincidence logic. Here, we experimentally implement a new protocol, “stimulated-emission tomography” (SET), allowing us to obtain the information provided by QST when the photon pairs are generated by parametric fluorescence. This approach exploits a stimulated process that results in a signal several orders of magnitude larger than in QST. In particular, we characterize the polarization state of photons that would be generated in spontaneous parametric downconversion using SET. We find that SET accurately predicts the purity and concurrence of the spontaneously generated photons in agreement with the results of QST. We expect that SET will be extremely useful to characterize entanglement sources based on parametric fluorescence, providing a fast and efficient technique to potentially replace or supplement QST.