Quantum Information Science at UBC

Research

  • Quantum Information and Computation
  • QI and foundational aspects of quantum mechanics
  • Qubits with photons, quantum dots (Experiment)
  • Fault-tolerance and decoherence
  • Entanglement

Researchers

QI seminar@UBC

Featured publications

UBC QMI & Max Planck: Upcoming workshop announcement

QI10 archive

Pradeep Sarvepalli analyzing counterexamples to the so-called LU/LC conjecture.

Research


Our work is in quantum information, ranging from theoretical work on `Models of quantum computation' and quantum fault-tolerance to experiments on decoherence, quantum dots and topologically protected qubits.

Featured publication: Experimental demonstration of topological error correction. [Posted June 7, 2012] Here we report the experimental demonstration of topological error correction with an eight-photon cluster state. We show that a correlation can be protected against a single error on any quantum bit. Also, when all quantum bits are simultaneously subjected to errors with equal probability, the effective error rate can be significantly reduced. Our work demonstrates the viability of topological error correction for fault-tolerant quantum information processing.

The present experiment uses an 8-qubit cluster state which shares topological features with its larger (potentially much larger) cousin, the three-dimensional cluster state. A 3D cluster state is for measurement-based quantum computation (MBQC) what the Kitaev surface code is for the circuit model: a fault-tolerant fabric in which protected quantum gates can be implemented in a topological fashion. The present experiment demonstrates the fault-tolerance properties, not yet the encoded quantum gates. For the latter, larger cluster states will be required in future experiments. The smallest possible setting to demonstrate topological error-correction with cluster states requires 8 qubits, which was just in reach of the present photon-based experiment.

Journal Reference: Xing-Can Yao et al, Experimental demonstration of topological error correction, Nature 482, 489 (2012).
Also see James D. Franson, Quantum computing: A topological route to error correction, Nature 482, News and Views, (2012).

Topological error correction with cluster states.
(left) Measurement of the error in the topologically protected correlation of the cluster state (0: perfect correlation, 0.5: no correlation, 1: perfect anti-correlation), vs. the one qubit error rate. The local errors are subjected to the cluster state on purpose, with varying strength. The black curve is the theory prediction for the strength of the correlation vs local error rate, if no error correction is performed, and the red dashed curve is for the same correlation with error correction performed. The dots represent the measured data. For small error probabilities, topological error correction significantly reduces logical error.
(right) What do the 8-qubit cluster state used in the experiment and a large 3D cluster state have in common? - Both can be described by an underlying three-dimensional chain complex. Their topological error protection derives from the homology properties of these complexes.



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Researchers & students


Faculty in quantum information science

Robert Raussendorf
Assistant Professor in Physics
Office: Hennings 338
Tel.: (604) 822-3253
email: raussen[at]phas[dot]ubc[dot]ca
Research: Quantum computation , My research interest is in quantum computation, in particular computational models. I have invented the one-way quantum computer (QCc) together with Hans Briegel (UK patent GB 2382892, US patent 7,277,872). The QCc is a scheme of universal quantum computation by local measurements on a suitable multi-particle entangled quantum state. Quantum information is written onto the initial state, processed and read out by one-qubit measurements only. As the computation proceeds, the entanglement in the resource state is progressively destroyed. Measurements replace unitary evolution as the elementary process driving a quantum computation. I also work in quantum error-correction and on connections between quantum computation and foundations of quantum mechanics.

See: R. Raussendorf and J. Harrington, Fault-tolerant quantum computation with high threshold in two dimensions, arXiv:quant-ph/0610082, Phys. Rev. Lett. 98, 150504 (2007).

Faculty with accomplishments and research interests in quantum information

Andrea Damascelli
Associate Professor in Physics
Office ,
Tel.: (604) 822-
email:
Research: Andrea Damascelli is Canada Research Chair in the Electronic Structure of Solids, and the leader of the Quantum Materials Laboratory at UBC and of the Quantum Materials Spectroscopy Center at the Canadian Light Source. His research program utilizes high resolution spectroscopic techniques based on ultraviolet and soft x-ray synchrotron radiation, in particular spin and angle-resolved photoemission spectroscopy (S+ARPES), to investigate the electronic structures of quantum materials, such as unconventional superconductors, novel magnets, and topological insulators. In the area of quantum information, his group is working on the development of a device based on materials with novel quantum properties, to be implemented as a key component in spintronics and quantum computing; the device will hold a macroscopic and robust quantum state at the interface between a superconductor and the recently discovered topological insulator.
Josh Folk
Associate Professor in Physics
Office ,
Tel.: (604) 822-
email:
Research: Our group measures the electronic properties of nanometer- and micron-scale devices at temperatures from 0.01K to 1K, where electronic transport is dominated by quantum mechanical effects. Many of our experiments focus on electron spin, because spin is the quantum degree of freedom that is most resilient to environmental decoherence. Specific projects currently underway include spin current control and measurement in GaAs circuits, decoherence and Kondo interactions in quantum dots, and graphene nanoelectronics.
Kirk Madison
Associate Professor in Physics
Office ,
Tel.: (604) 822-
email:
Research: Quantum gases. My background is in the study of few and many-body quantum phenomena using laser cooled atomic gases. Career accomplishments include the first observation of the non-exponential decay of an unstable quantum system (a fundamental prediction of quantum mechanics which was only verified experimentally 40 years after it was originally proposed), the study of Bloch oscillations and Wannier-Stark states using cold atoms trapped in optical lattices (phenomena in the field of quantum transport) , and the first experimental realization of vortex nucleation in an atomic Bose Einstein condensate. My research now is aimed at realizing quantum gases of molecules assembled from laser cooled atomic gases. Recent achievements at UBC on this topic include the production of a Bose Einstein condensate of ultra-cold Lithium molecules.
Takamasa Momose
Professor (Chemistry)
Office: Chem A327
Tel: (604-822-5401)
email:momose@chem.ubc.ca
Research: High-resolution infrared and visible spectroscopy; laser spectrosopy; low temperature chemistry; tunneling reactions; making cold molecules; quantum computation.
Mark van Raamsdonk
Associate Professor in Physics
Office Henn 420
Tel.: (604) 822-2138
email:
Research: My research is focused on string theory, quantum gravity and quantum field theory. In recent work, I and others have found intriguing evidence that the emergence of spacetime in quantum gravity is intimately connected to the quantum entanglement of some fundamental underlying degrees of freedom. This suggests the dramatic result that the existence of a classical spacetime is related to the fundamentally quantum mechanical phenomenon of entanglement. Quantitatively, there is evidence that certain measures of entanglement in the underlying degrees of freedom are directly related to geometrical quantities (certain areas or volumes) in the corresponding spacetime. My current research is focused on exploring these connections between quantum information theory and quantum gravity. I have also recently introduced and studied novel quantum information theoretic observables in the context of quantum field theory.

See: Mark Van Raamsdonk, , Gen. Relativ. Gravit. (2010) 42:2323 arXiv:1005.3035

Moshe Rozali
Associate Professor in Physics
Office
Tel: (604) 822-
email:
Research: My main research interests involve string theory as extension of quantum field theory that includes quantum gravitational phenomena, and relatedly -- describing strongly coupled systems. As such, string theory has diverge applications to many areas of physics. My main interest in quantum information is the question on whether quantum field theory provides additional resources for quantum computation, above and beyond quantum mechanics with finitely many degrees of freedom. String theory related techniques to calculating quantum field theory amplitudes may be useful in shedding light on this issue.

Gordon Semenoff
Professor of Physics
Office ,
Tel.: (604) 822-
email:
Research: String theory and condensed matter physics. In quantum information: I am interested in the interplay between issues in quantum information theory and topological phenomena, such as the formation of mid-gap bound states of electrons interacting with vortices and domain walls, particularly how quantum information is encoded in such states.

See: P. Sodano and G.W. Semenoff, Stretching the Electron as far as it will go, arXiv:cond-mat/0605147.

Philip Stamp
Professor of Physics
Office
Tel: (604) 822-
email:
Research: Strongly-correlated quantum matter: quantum magnetism, coherence phenomena in biological systems, quantum spin nets and qubits. One of the most exciting challenges in physics is to devise networks of 'qubits' (ie., quantum 2-level systems) which can behave as a quantum information processing system. In our view the most promising candidates for the qubits are electronic and/or nuclear spins, provided the fundamental problem of decoherence can be brought under control.

See: N.V. Prokof'ev, P.C.E. Stamp, Theory of the Spin Bath Rep. Prog. Phys. 63, 669-726 (2000).

Bill Unruh
Professor of Physics
Office
Tel.: (604) 822-
email:
Research: Quantum Mechanics and General Relativity.
Konrad Walus
Associate Professor in Electrical Engineering
Office Kaiser 4038
Tel.: (604) 822-4060
email:
Research: Konrad Walus has contributed to the development of design tools, theoretical models, and circuits for an emerging nanotechnology based on the coupled dynamics of locally-interacting finite-state nanostructures, specifically the paradigm called quantum-dot cellular automata (QCA). QCA has demonstrated some benefits to traditional CMOS based technologies for realizing high density logic including lower predicted power dissipation and scaling limits in the atomic size range. QCA has also been explored as a platform for conducting quantum information processing and this work is still ongoing. QCA devices and circuits have been realized in several platforms including coupled metallic-islands, nano-magnetics, and more recently in silicon.

See: Marco Taucer, Faizal Karim, Konrad Walus, Robert A. Wolkow, Consequences of Many-cell Correlations in Treating Clocked Quantum-dot Cellular Automata Circuits/span>, arXiv:1207.7008 (cond mat).

Jeff Young
Professor of Physics
Lab: AMPEL,
Tel.: (604) 822-8779
email: young@phas.ubc.ca

Research: NanoPhotonics. My group develops waveguide-based optical "circuits" that concentrate and manipulate infrared radiation on micrometre length scales. Much of our past work has focussed on demonstrating how the nanophotonic components of these circuits can be used to enhance the effective interaction strength of light and electrons, as evidenced by the observation of nonlinear optical responses at power levels much lower than typically required in bulk materials. Our main QI related project incorporates colloidal, 5 nm diameter PbSe quantum dots, site-selectively located in a photonic crystal microcavity fabricated in silicon-on-insulator wafers, as discrete quantum oscillators that preferentially decay by exciting a photon in the microcavity. This photon is then efficiently coupled to a single mode silicon waveguide that can transport the photon with low loss to other circuit elements on the chip. With further development, this could be developed into a room temperature, integrated single-photon source.
Fei Zhou
Associate Professor in Physics
Office Hennings 345
Tel.: (604) 822-5098
email:
Research in QI: To understand the dynamics of atom-based fault tolerant quantum information storages and quantum computers; and to design topological quantum computing states in optical lattices.

Postdocs

Raouf Dridi
Postdoc
email: dridi.raouf[at]gmail[dot]com.
Research: Quantum Foundations and computer algebra.

Leon Loveridge
Postdoc
email: Leon[at]phas[dot]ubc[dot]ca
Research: Quantum Measurement Theory.

Vijay Singh
Postdoc (Main appointment with Petr Lisonek/ SFU Math)
email: vijay.k.1[at]gmail[dot]com
Research: Quantum coding theory. The LU/LC conjecture.

Students

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

Research: quantum information. Quantum codes and tensor networks.

Cihan Okay
Graduate Student at PIMS
Supervisor: Alejandro Adem
Office: WMAX 208, Tel: 604-822-0411
email: okay[at]math[dot]ubc[dot]ca
Research: My research interest in Algebraic Topology can be summarized as group cohomology and homotopy colimits of classifying spaces. As for physics and quantum information, my interest is in topological quantum computation.

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

Research: Fault-tolerant quantum computation.



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