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arXiv:1304.2101 · New Journal of Physics

Controllable generation of mixed two-photon states

Jibo Dai, Yink Loong Len, Yong Siah Teo, Leonid A. Krivitsky, Berthold‐Georg Englert

Published Jun 10, 2013• 6 citations
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Abstract

We report a controllable method for producing mixed two-photon states via spontaneous parametric down-conversion with a two-type-I crystal geometry. By using variable polarization rotators (VPRs), one obtains mixed states of various purities and degrees of entanglement depending on the parameters of the VPRs. The generated states are characterized by quantum state tomography. The experimental results are found to be in good agreement with the theory. The method can be easily implemented for various experiments that require the generation of states with controllable degrees of entanglement or mixedness.

DOI
10.1088/1367-2630/15/6/063011

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We report a controllable method for producing mixed two-photon states via spontaneous parametric down-conversion with a two-type-I crystal geometry. By using variable polarization rotators (VPRs), one obtains mixed states of various purities and degrees of entanglement depending on the parameters of the VPRs. The generated states are characterized by quantum state tomography. The experimental results are found to be in good agreement with the theory. The method can be easily implemented for various experiments that require the generation of states with controllable degrees of entanglement or mixedness.
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Abstract A parametric source of polarization entangled photon pairs with peculiar spatial characteristics allows to generate any kind of bi‐partite entangled states with tunable dgree of entanglement and mixedness. In particular, maximally entangled mixed states (MEMS) have been created in a reliable way by a “patchwork” technique and investigated by quantum tomography. By the same source, momentum‐polarization hyper‐entangled two‐photon states have been synthesized. The quality of the entanglement in the two degrees of freedom has been tested by multimode Hong‐Ou‐Mandel interferometry.
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A parametric source of polarization-entangled photon pairs with striking spatial characteristics is reported. The distribution of the output electromagnetic k\mathbf{k}k modes excited by spontaneous parametric down-conversion and coupled to the output detectors can be very broad. Using these states realized over a full entanglement ring output distribution, the nonlocal properties of the generated entanglement have been tested by standard Bell measurements and by Ou-Mandel interferometry. A ``mode-patchwork'' technique based on the quantum superposition principle is adopted to synthesize in a straightforward and reliable way any kind of mixed state, of large conceptual and technological interest in modern quantum information. Tunable Werner states and maximally entangled mixed states have indeed been created by this technique and investigated by quantum tomography. A study of the entropic and nonlocal properties of these states has been undertaken experimentally and theoretically, by a unifying variational approach.