Entanglement gain in measurements with unknown results

• Published in: Physical Review A
• Main Authors: Zuppardo, Margherita, Ganardi, Ray, Miller, Marek, Bandyopadhyay, Somshubhro, Paterek, Tomasz
• Other Authors: Raunvísindastofnun (HÍ), Science Institute (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Physical Society (APS) 2019
• Subjects: Quantum entanglement; Global measurements; Two particles; Skammtafræði; Atóm; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/1774; https://doi.org/10.1103/PhysRevA.99.042319

Publisher's version (útgefin grein) We characterize nonselective global projective measurements capable of increasing quantum entanglement between two particles. In particular, by choosing negativity to quantify entanglement, we show that entanglement of any pure nonmaximally entangled state can be improved in this way (but not of any mixed state) and we provide detailed analysis for two qubits. It is then shown that Markovian open system dynamics can only approximate such measurements, but this approximation converges exponentially fast as illustrated using the Araki-Żurek model. We conclude with numerical evidence that macroscopic bodies in a random pure state do not gain negativity in a random nonselective global measurement. We thank Michał Horodecki, Kavan Modi, Aby Philip, and Somasundaram Sankaranarayanan for discussions. S.B. thanks Anindita Banerjee and Saronath Halder for helpful discussions. This work is supported by Singapore Ministry of Education Academic Research Fund Tier 2 Project No. MOE2015-T2-2-034. S.B. is supported, in part, by SERB Project No. EMR/2015/002373. M.Z. is supported by the Icelandic Research Fund, Grant No. 163082-051. Some of the computations were performed on resources provided by the Icelandic High Performance Computing Centre at the University of Iceland. Peer Reviewed