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Sarah Croke

Portrait de Sarah Croke
University of Glasgow - Department of Physics and Astronomy

Area of Research:
Phone: x6521

Research Interests

I am interested in both theoretical development and experimental implementations of quantum information protocols. On the theoretical side, my current research focuses on protocols that require only a small quantum processor, and thus may be implementable with current or near future technology, while in the past I have worked on strategies for discriminating optimally between quantum states - an important primitive in quantum information and communications. On the experimental side, I have collaborated with experimental groups, most recently with Kevin Resch's group at IQC, on optical demonstrations of quantum state discrimination strategies.

Together with collaborators Robin Blume-Kohout and Daniel Gottesman, my recent work has been to develop a streaming implementation of entanglement concentration - that is, one which reads in non-maximally entangled quantum systems one at a time, performs some processing, and outputs maximally entangled states as they are produced. This work also explores how a quantum processor learns about the quantum information input, and can use this information to improve performance in processing subsequent qubits. Unlike in the classical case, a quantum processor must do this coherently, and so stores "quantum knowledge" of the quantum state. My current research extends these ideas to state discrimination and quantum data compression.

In a previous life I was (briefly) a radio astronomer, studying quasars, among the brightest objects in the sky at all frequencies at which they have been observed. Some of my recent papers are in this field.

Positions Held

  • 2007 - 2011 Perimeter Institute, Postdoctoral Fellow (on leave March 2010 - March 2011; part time March 2011 - July 2011)
  • 2004 - 2007 Department of Physics, University of Strathclyde and Department of Mathematics, University of Glasgow PhD student

Recent Publications

  • Minimum-error discrimination of entangled quantum states, Yang Lu, Nick Coish, Rainer Kaltenbaek, Deny R. Hamel, Sarah Croke, Kevin J. Resch, Phys Rev A 82, 042340 (2010), arxiv:quant-ph/1008.0843
  • Phase Evolution in Spatial Dark States, S. McEndoo, S. Croke, J. Brophy, Th. Busch, Phys Rev A 81, 043640 (2010), arxiv:quant-ph/1001.3961
  • The parsec-scale distributions of intensity, linear polarization and Faraday rotation in the core and jet of Mrk501 at 8.4-1.6 GHz, S. M. Croke, S. P. O'Sullivan, D. C. Gabuzda, Monthly Notices of the Royal Astronomical Society 402, 259-270 (2010)
  • Quantum state discrimination, Stephen M. Barnett, Sarah Croke, Advances in Optics and Photonics 1, 238-278 (2009), arxiv:quant-ph/0810.1970
  • On the conditions for discrimination between quantum states with minimum error, Stephen M. Barnett, Sarah Croke, Journal of Physics A 42, 062001 (2009) arxiv:quant-ph/0810.1919
  • Aligning VLBI Images of Active Galactic Nuclei at Different Frequencies, S. M. Croke, D. C. Gabuzda, Monthly Notices of the Royal Astronomical Society 386, 619-626 (2008) arxiv:astro-ph/0809.3313
  • No-Signalling Bound on Quantum State Discrimination, Sarah Croke, Erika Andersson, Stephen M. Barnett, Phys Rev A 77, 012113 (2008) arxiv:quant-ph/0708.3909
  • Experimental Realization of Maximum Confidence State Discrimination for the Extraction of Quantum Information, Peter J. Mosley, Sarah Croke, Ian A. Walmsley, Stephen M. Barnett, Phys Rev Lett 97, 193601 (2006), arXiv: quant-ph/0610237
  • Maximum Confidence Quantum Measurements, Sarah Croke, Erika Andersson, Stephen M. Barnett, Claire R. Gilson, John Jeffers, Phys Rev Lett 96, 070401 (2006), arXiv: quant-ph/0604026
  • Ideal state discrimination with an O(1)-qubit quantum computer, Robin Blume-Kohout, Sarah Croke, Michael Zwolak, arXiv: 1201.6625
  • Longer-Baseline Telescopes Using Quantum Repeaters, Daniel Gottesman, Thomas Jennewein, Sarah Croke, arXiv: 1107.2939
  • Streaming universal distortion-free entanglement concentration, Robin Blume-Kohout, Sarah Croke, Daniel Gottesman, arXiv: 0910.5952
  • Noiseless linear amplification via weak measurements, David Menzies, Sarah Croke, arXiv: 0903.4181


  • Quantum Key Distribution, Quantum Cryptography School for Young Students (QCSYS), IQC, Waterloo (July 2009, July 2010, Aug 2011)
  • Streaming universal entanglement concentration, Quantum Information Science workshop, KITP, Santa Barbara, USA
  • Maxmimum confidence measurements, RCQI, Bratislava, Slovakia
  • Approximating quantum operations using weak values, University of Bristol, UK
  • Quantum state discrimination and the no-signaling principle, IQC Seminar, Waterloo
  • Maximum confidence measurements, Hunter College, New York, USA
  • PIRSA:11090047, Differential Equations - Lecture 4, 2011-09-02, 11/12 PSI - Orientation Weeks
  • PIRSA:11080142, Differential Equations - Lecture 3, 2011-08-31, 11/12 PSI - Orientation Weeks
  • PIRSA:11080141, Differential Equations - Lecture 2, 2011-08-29, 11/12 PSI - Orientation Weeks
  • PIRSA:11080136, Differential Equations - Lecture 1, 2011-08-25, 11/12 PSI - Orientation Weeks
  • PIRSA:11080082, Presentation Preparation, 2011-08-17, 11/12 PSI - Orientation Weeks
  • PIRSA:11080149, Life as a Physicist, 2011-08-04, ISSYP
  • PIRSA:09100011, The Art of Guesstimation, 2009-10-17, Quantum to Cosmos Festival - Tickets Available starting TUE. Sep 8, 2009
  • PIRSA:08030009, Quantum Information Theory #4, 2008-03-20, New Horizons In Fundamental Physics
  • PIRSA:08030005, Quantum Information Theory #3, 2008-03-18, New Horizons In Fundamental Physics
  • PIRSA:08030008, Quantum Information Theory #2, 2008-03-13, New Horizons In Fundamental Physics
  • PIRSA:08030004, Quantum Information Theory #1, 2008-03-11, New Horizons In Fundamental Physics
  • PIRSA:06120040, TBA, 2006-12-08, Young Researchers Conference - 2006