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25 May 2004 Benchmarking and procrustean noise reduction of entangled mixed states
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Proceedings Volume 5468, Fluctuations and Noise in Photonics and Quantum Optics II; (2004)
Event: Second International Symposium on Fluctuations and Noise, 2004, Maspalomas, Gran Canaria Island, Spain
Understanding quantum noise is essential for accurately creating desired quantum states and for examining a given state's evolution in any protocol. Using spontaneous parametric downconversion, we can create a wide variety of single- and two-qubit polarization states, including nearly perfect Bell states, mixed states (i.e., "noisy" states) and maximally entangled mixed states (MEMS). To characterize these states we use several different measures, including fidelity, "tangle" and linear entropy. In the course of our experiments, we have discovered and numerically investigated an extreme imbalance in the sensitivity of these different two-qubit state measures. We have also experimentally realized a "Procrustean" filtering technique to remove noise from MEMS. For moderate amounts of filtering, the experimental procedure works as desired to increase the tangle and decrease the linear entropy. However, for large amounts of filtering, the process becomes dominated by perturbations in the starting density matrix. The final outcome is a pure (i.e., zero entropy) product state (i.e., zero entanglement).
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Nicholas A. Peters, Tzu-Cheih Wei, and Paul G. Kwiat "Benchmarking and procrustean noise reduction of entangled mixed states", Proc. SPIE 5468, Fluctuations and Noise in Photonics and Quantum Optics II, (25 May 2004);

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