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Fortschritte der Physik

Generation of (2 × 2) and (4 × 4) two‐photon states with tunable degree of entanglement and mixedness

Marco Barbieri, C. Cinelli, F. De Martini, Paolo Mataloni

Published Oct 11, 2004• 9 citations
Publisher

Abstract

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.

DOI
10.1002/prop.200410180

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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.
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.
Maximally entangled states, Werner state and maximally entangled mixed states (MEMS) have been created and fully characterized by a novel high brilliance universal source of entangled photon pairs with striking spatial characteristics. Mixed states of any structure, spanning a 2 x 2 Hilbert space may be created by this source. The non local properties of the generated entanglement have been tested by standard Bell measurements. Tunable Werner states and Maximally Entangled Mixed States (MEMS) have been created by an original patchwork technique and investigated by quantum tomography. The entropic and nonlocal properties of these states have been also undertaken.
Two quantum interferometry processes with possible significant applications in quantum information technology are presented. A two frequency Mach‐Zehnder interferometer realizes the nonlinear frequency conversion of a single photon qubit. The information‐preserving character of the nonlinear process allows to transfer the coherence of the input to the output state. Furthermore, we describe a novel high brilliance universal source of entangled photon pairs with peculiar spatial characteristics, which allows to generate two particle entangled states, either pure or mixed of any structure. By this source we have synthesized and fully characterized by quantum tomography Werner states and maximally entangled mixed states (MEMS). The non local properties of these states have been tested by Bell measurements.