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arXiv:1006.5116 · New Journal of Physics

Spectrally resolved quantum tomography of polarization-entangled states

Dmitry A. Kalashnikov, Leonid A. Krivitsky

Published Sep 24, 2010• 0 citations
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Abstract

We studied the broadband polarization entangled states generated within the linewidth of type-II spontaneous parametric down conversion (SPDC). Applying a complete quantum polarization tomography protocol at an arbitrary combination of frequency and angular sideband modes, we reveal the complex structure of non-degenerate non-collinear polarization-entangled states generated within the SPDC linewidth. We demonstrate that the simultaneous compensation of longitudinal and transverse walk-off leads to homogenization of the structure of polarization entanglement.

DOI
10.1088/1367-2630/12/9/093040

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We studied the broadband polarization entangled states generated within the linewidth of type-II spontaneous parametric down conversion (SPDC). Applying a complete quantum polarization tomography protocol at an arbitrary combination of frequency and angular sideband modes, we reveal the complex structure of non-degenerate non-collinear polarization-entangled states generated within the SPDC linewidth. We demonstrate that the simultaneous compensation of longitudinal and transverse walk-off leads to homogenization of the structure of polarization entanglement.
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We study the frequency-angular line shape for a phase-matched nonlinear process producing entangled states and show that there is a continuous variety of maximally entangled states generated for different mismatch values within the natural bandwidth. Detailed considerations are made for two specific methods of polarization entanglement preparation, based on type-II spontaneous parametric down-conversion (SPDC) and on SPDC in two subsequent type-I crystals producing orthogonally polarized photon pairs. It turns out that different Bell states are produced at the center of the SPDC line and on its slopes, corresponding to about half-maximum intensity level. These Bell states can be filtered out by either frequency selection or angular selection, or both. Our theoretical calculations are confirmed by a series of experiments, performed for the two above-mentioned schemes of producing polarization-entangled photon pairs and with two kinds of measurements: frequency selective and angular selective.
In this paper we review our recent works on the generation of different Bell states within the lineshape of parametric down-conversion (SPDC) and their possible applications. Indeed, for polarization-entangled two-photon states produced via SPDC, the frequency-angular lineshape allowed by phase matching is considered. It is shown that there are always different Bell states generated for different mismatch values within the natural bandwidth. Consideration is made for two different methods of polarization entanglement preparation, based on type-II SPDC and on SPDC in two type-I crystals producing orthogonally polarized photon pairs. Different Bell states can be filtered out by either frequency selection or angular selection, or both. Our theoretical calculations are confirmed by a series of experiments, performed for the two above-mentioned ways of producing polarization-entangled photon pairs and with two kinds of measurements: frequency-selective and angular-selective. Finally, we mention possible application to quantum communication with fibers.