Robert Raussendorf's Quantum Information group at UBC Physics

Group members


  • Quantum Information and Computation
  • QI and quantum foundations
  • Quantum fault-tolerance

QI seminar@UBC


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Our work is in quantum information, specifically `Models of quantum computation' and quantum fault-tolerance. For more information click here.

Featured publication: Wigner Function Negativity and Contextuality in Quantum Computation on Rebits. [Posted May 4, 2015] We describe a universal scheme of quantum computation by state injection on rebits (states with real density matrices). For this scheme, we establish contextuality and Wigner function negativity as computational resources, extending results of M. Howard et al. [Nature (London) 510, 351 (2014)] to two-level systems. For this purpose, we define a Wigner function suited to systems of multiple rebits and prove a corresponding discrete Hudson's theorem. We introduce contextuality witnesses for rebit states and discuss the compatibility of our result with state-independent contextuality.

Journal Reference: Nicolas Delfosse, Philippe Allard Guerin, Jacob Bian, and Robert Raussendorf, Wigner Function Negativity and Contextuality in Quantum Computation on Rebits, Phys. Rev. X 5, 021003 (2015).


Negativity and contextuality for rebits. Left: Rebit Wigner function of a three-qubit graph state. This state is local unitary equivalent to a Greenberger-Horne-Zeilinger (GHZ) state. Negativity of the Wigner function for the three-qubit graph state indicates non-classicality. Contrary to qudits in odd prime dimension, for rebits negativity is not synonymous wit contextuality. Nevertheless, the negativity in the Wigner function for the three-qubit graph state is strong enough to witness contextuality. Right: From the perspective of contextuality in quantum computation with magic states, Mermin's square and star, and all their cousins, are ``little monsters''. For explanation, see below.

State-independent contextuality, as exhibited by Mermin's square and star, provides beautifully simple proofs for the Kochen-Specker theorem in dimension 4 and higher. However, for establishing contextuality as a resource only posessed by magic states, state-independent contextuality poses a problem: If ``cheap'' Pauli measurements already have contextuality, then how can one say that contextuality is a key resource provided by the magic states? For qudits, the problem doesn't exist because there is no state-independent contextuality w.r.t. Pauli measurements. For rebits, the problem is overcome by the operational restriction to CSS-ness preserving gates and measurements.

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Group members

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Robert Raussendorf
Associate Professor
Hennings 338, Tel.: (604) 822-3253
email: raussen[at]phas[dot]ubc[dot]ca

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Poya Haghnegahdar
Graduate Student (PhD)
email: phaghneg[at]phas[dot]ubc[dot]ca

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Philippe Allard Guerin
Graduate student (Masters)
email: pallard[at]phas[dot]ubc[dot]ca

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Navid Siami
Graduate student (Masters)
email: navidsiami[at]gmail[dot]com

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Arman Zaribafiyan
Graduate Student (PhD)
email: zaribafiyan[at]gmail[dot]com

Former group members


Tzu-Chieh Wei, faculty at Stony Brook, NY, USA
Pradeep Sarvepalli, faculty at IIT Madras, Chennai, India
Leon Loveridge, University of Oxford, UK
Raouf Dridi
Vijay Singh


Angela Ruthven (UBC Enginerring Physics)
Len Goff (UBC Economics)
Matthew Scholte
Cedric Lin (MIT),
Matthew Low (University of Chicago),
Philip Ketterer (Ludwig Maximilians University Munich, Germany),
Philip Allen Mar (University of Toronto),
Cihan Okay (University of Western Ontario)

Group publications

2015 - Journal publications

2014 - Journal publications

2013 - Journal publications

2012 - Journal publications

2011 - Journal publications

2010 - Journal publications

2009 - Journal publications

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