iCORE Quantum Information Science @ University of Calgary Mini-Conference

28 May 2009 in SS117

Hosted by IQIS at the University of Calgary.



8:50 Arrival, commencement
9:00 Talk (Artur Scherer)
9:30 Talk (Peng Xue)
10:00 Talk (Nathan Wiebe)
10:30 Coffee/Tea and Posters
11:15 Talk (Aidan Roy)
11:45 Talk (Lo´ck Magnin)
12:15 Lunch


13:45 Talk (Yunjiang Wang)
14:15 Talk (Alexander Hentschel)
14:45 Talk (Jeong San Kim)
15:15 Coffee/Tea and Posters
16:00 Talk (Zahra Shaterzadeh Yazdi)
16:30 Talk (Ben Fortescue)
17:00 Talk (Jaewoo Joo)
17:30 Discussion
17:45 Closure, Departure



Conference Program:




Artur Scherer 

Title: Quantum states prepared by real-world entanglement swapping

: Entanglement swapping between photon pairs is a fundamental building block in schemes using quantum relays or quantum repeaters to overcome the range limits of long distance quantum key distribution. We develop a theory to calculate the actual quantum states prepared by realistic entanglement swapping, which takes into account experimental deficiencies due to inefficient detectors, detector dark counts and multi-photon-pair contributions of parametric down conversion sources. We investigate how the entanglement present in the final state of the remaining modes is affected by the real-world imperfections. To test the predictions of our theory, comparison with experimental entanglement swapping is provided. Current efforts towards generalizing our results to iterations of several concatenated noisy entanglement swappings are of particular relevance to research on long distance quantum communication.



Peng Xue

Title: Implementating quantum walks

Abstract: The random walk (RW), which is ubiquitous in physics, chemistry, mathematics, and computer science, underpins Brownian motion and diffusion processes, is used in satisfiability proofs, and is intimately connected with the Wiener measure. Quantization of the RW has led to new quantum algorithms and fascinating physics such as decoherence-induced diffusion reduction. Our goal is to see the quantum walk (QW) realized in the laboratory. However, compromises have to be made to the ideal QW in order to realize the QW experimentally, such as side-stepping the requirement of direct coin flipping in cavity quantum electrodynamics (QED) and finding an alternative to measuring the position distribution for a quantum walk in an ion trap. Here we discuss how QW can be implemented by making compromises to the ideal QW but nonetheless demonstrating a true QW in the laboratory.



Nathan Wiebe

Title: Quantum Computer Simulations of Time Dependent Hamiltonians

Abstract: Feynman's original motivation for the quantum computer resulted from a conjecture that quantum computers could efficiently simulate any quantum system, whereas classical computers cannot. Since then many quantum simulation schemes have verified his conjecture for sparse time independent Hamiltonians. However no scheme has yet been proposed that shows that time dependent quantum systems can be efficiently simulated while accounting for all computational resources and promises about the Hamiltonian. In this presentation I will show that many non-sparse time dependent Hamiltonians can be efficiently simulated, while accounting for all resources used in the simulation and that a trade-off exists between the performance of the simulation scheme and the information that the scheme is provided about the derivatives of the Hamiltonian.



Aidan Roy

Title: Bounds for unitary designs

Abstract: A unitary design is a finite collection of unitary matrices that approximate the entire unitary group. Such designs have a number of important applications in quantum information, including quantum process tomography and algorithm derandomization. In this talk, we find a lower bound for the size of a unitary t-design in U(d), for any d and t, and construct some designs of reasonable size. This is joint work with Andrew Scott.



Lo´ck Magnin

Title: A strong no-go theorem for quantum bit commitment.

Abstract: Unconditionally secure bit commitment is forbidden by Quantum Mechanics. We extend this no-go theorem to protocols where both players are restricted to Gaussian states and Gaussian operations which is a realistic assumption in the current state of the art for large scale implementations. We also give cheating strategies for any continuous-variable quantum bit commitment protocol. (work in collaboration with A. Leverrier, F. Magniez and N. J. Cerf)


  Yunjiang Wang 

Title: Feedback Iterative decoding of sparse quantum codes

Abstract: For pauli channels, we show that the inability to measure every qubit of a sparse quantum code severely limits decoding based on belief propagation. To overcome this measuement problem, we revise the belief propagation menthod by introducing a new heuristic feedback-based belief propagation strategy. Our approach incorporates feedback from individual qubit measurements that are automatically revealed by stabilizer measurements, and we demonstrate that our modification to the belief propagation approach yields a significantly lower block error rate for quantum decoding.



Alexander Hentschel

Title:  Machine Learning for Adaptive Quantum Control and Measurement

Abstract: For many applications, like atomic clocks or gravitational wave detection, it is essential to precisely ascertain an optical phase. The goal of quantum measurement is to get as close to the fundamental Heisenberg limit as possible. I will present a method for designing measurement protocols that are closest to the Heisenberg limit. Our approach is based on a self-learning particle swarm algorithm that is trained on a simulated experiment to perform optimal phase estimation. Our algorithm learns solely based on training without any knowledge about the physical system. I will explain how this technique can be extended such that the machine learning algorithm can be trained on a real wold experiment.



Jeong San Kim  

Title: Polygamy relations of entanglement in multipartite quantum systems.  

Abstract: While quantum entanglement is known to be monogamous (i.e. shared entanglement is restricted in multi-partite settings), here we show that distributed entanglement (or the potential for entanglement) is by nature polygamous. By establishing the concept of one-way unlocalizable entanglement (UE) and investigating its properties, we provide a polygamy inequality of distributed entanglement in tripartite quantum systems of arbitrary dimension. We also provide a polygamy inequality in multi-qubit systems, and several trade offs between UE and other correlation measures.



Zahra Shaterzadeh Yazdi

Title: Quantum Computing with Dangling Bond pairs on a Silicon Surface

Abstract: Quantum computing enables certain intractable computational problems to be solved faster and more efficient than would ever be possible with existing classical computers. We propose quantum computation with charge qubits on a Si(100) surface. The charge qubit corresponds to an excess electron shared between a pair of nearby dangling bonds, which are created by selectively removing Hydrogen atoms from the surface. Gate controls are implemented by making local potential differences. The advantages of our scheme over proposed bulk silicon quantum computing are long coherence times and direct control and readout of the surface.This scheme builds on a successful demonstration of quantum-dot cellular automata with dangling bonds and address all five DiVincenzo criteria.



Ben Fortescue 

Title: State-merging and generalising asymptotic entanglement of assistance

Abstract: I will discuss the Horodecki-Oppenheim-Winter state-merging protocol and its application to the asymptotic conversion of multipartite pure states to singlets under LOCC, including achievable bounds on conversion rates and the relation of such protocols to single-copy "random distillation". (This talk overlaps with my earlier seminar on this subject).



Jaewoo Joo 

Title: Error-correcting one-way quantum computation

Abstract: We present an approach to one-way quantum computation (1WQC) that can compensate for single-qubit errors, by encoding the logical information residing on physical qubits into five-qubit error-correcting code states. A logical two-qubit cluster state that is the fundamental resource for encoded quantum teleportation is then described by a graph state containing ten vertices with constant degree seven. Universal 1WQC that incorporates error correction requires only multiple copies of this logical two-qubit state and a logical four-qubit linear cluster state, which are prepared only just in advance of their use in order to minimize the accumulation of errors. We suggest how to implement this approach in systems characterized by qubits in regular two-dimensional lattices for which entangling gates are generically global operations, such as atoms in optical lattices, quantum dots, or superconducting qubits.





Saleh Rahimi Keshari

Title: Quantum Process Estimation

Abstract: Quantum information processing systems require precise characterization of each component's properties and the underlying process that occur within quantum devices. The mathematical representation for describing quantum process that we shall employ relies on the Jamio³kowski isomorphism. By using maximum likelihood method, we shall see how a process can be characterized.



Ben Lavoie

Title: Mode Theory of Guided Electromagnetic Waves

Abstract: Some background on the behaviour of electromagnetic waves that are guided using dielectric layers or confined to cavities.



Sadeh Raeisi

Title: Studying Quantum Phase Transition Based on Matrix Product Representation of the Ground State*

Abstract: We present a formalism to derive set of equations governs on Matrix Product (MP) representation of the ground state of a given many body Hamiltonian with local interaction and a criterion to discuss the possibility of the existence of a Translational Invariant Matrix Product (TIMP) ground state. In addition, we propose a method to study Quantum Phase Transitions (QPTs) based on this formalism, and we make use of it to study XXZ spin one chain with uniaxial single-ion-type anisotropy and compare our results with previous numerical studies.



Michael Skotiniotis

Title: Relative parameter estimation of quantum states subject to a global super-selection rule.

Abstract: In the presence of a noisy quantum channel, or the absence of a classical reference frame, encoding information using the global degrees of freedom of a quantum system is problematic. For instance, a quantum channel that performs a fixed but unknown rotation to every system imposes severe restrictions on any task that utilizes spin to encode information. Equivalently, a party with access to systems with spin degrees of freedom, but no fixed Cartesian frame to denote direction, is severely restricted in the types of states and operation he or she can perform. In such cases one way to circumvent the nuisance of the noisy channel, or lack of reference frame, is by sending two physical systems.

Whenever a quantum system can be decomposed into two parts, information can be encoded into the degrees of freedom that describe the relations between the parts. Schemes for encoding and decoding information using relative degrees of freedom are advantageous. They obviate the need to estimate the action of the channel, which is costly in both time and resources. I will present optimal schemes for encoding and decoding information into the relative degrees of freedom of two quantum systems, when the unknown operation of the quantum channel belongs to a finite group of transformations.





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