Method for universal detection of two-photon polarization entanglement

Karol Bartkiewicz, Paweł Horodecki, Karel Lemr, Adam Miranowicz, and Karol Życzkowski
Phys. Rev. A 91, 032315 – Published 20 March 2015

Abstract

Detecting and quantifying quantum entanglement of a given unknown state poses problems that are fundamentally important for quantum information processing. Surprisingly, no direct (i.e., without quantum tomography) universal experimental implementation of a necessary and sufficient test of entanglement has been designed even for a general two-qubit state. Here we propose an experimental method for detecting a collective universal witness, which is a necessary and sufficient test of two-photon polarization entanglement. It allows us to detect entanglement for any two-qubit mixed state and to establish tight upper and lower bounds on its amount. A different element of this method is the sequential character of its main components, which allows us to obtain relatively complicated information about quantum correlations with the help of simple linear-optical elements. As such, this proposal realizes a universal two-qubit entanglement test within the present state of the art of quantum optics. We show the optimality of our setup with respect to the minimal number of measured quantities.

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  • Received 21 May 2014

DOI:https://doi.org/10.1103/PhysRevA.91.032315

©2015 American Physical Society

Authors & Affiliations

Karol Bartkiewicz1,2,*, Paweł Horodecki3,4, Karel Lemr2, Adam Miranowicz1, and Karol Życzkowski5,6

  • 1Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
  • 2RCPTM, Joint Laboratory of Optics of Palacký University and Institute of Physics of Academy of Sciences of the Czech Republic, 17 Listopadu 12, 772 07 Olomouc, Czech Republic
  • 3Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, 80-233 Gdańsk, Poland
  • 4National Quantum Information Centre in Gdańsk, 81-824 Sopot, Poland
  • 5Institute of Physics, Jagiellonian University, ul Łojasiewicza 11, 30-348 Krakow, Poland
  • 6Center for Theoretical Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02-668 Warsaw, Poland

  • *bark@amu.edu.pl

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Vol. 91, Iss. 3 — March 2015

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