iCORE Quantum Information Science @ University of Calgary MiniConference28 May 2009 in SS117Hosted by IQIS at the University of Calgary. 
Schedule:8:50 Arrival, commencement9:00 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 (Loïck Magnin) 12:15 Lunch 
13:45 Talk (Yunjiang Wang) 
Conference Program:


Title: Quantum states prepared by realworld entanglement swapping


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 decoherenceinduced 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 sidestepping 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.


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 nonsparse time dependent Hamiltonians can be efficiently simulated, while accounting for all resources used in the simulation and that a tradeoff exists between the performance of the simulation scheme and the information that the scheme is provided about the derivatives of the Hamiltonian.


Title: Bounds for unitary designs


Title: A strong nogo theorem for quantum bit commitment.


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 feedbackbased 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.


Title: Machine Learning for Adaptive Quantum Control and Measurement


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 multipartite settings), here we show that distributed entanglement (or the potential for entanglement) is by nature polygamous. By establishing the concept of oneway 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 multiqubit systems, and several trade offs between UE and other correlation measures.


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 quantumdot cellular automata with dangling bonds and address all five DiVincenzo criteria.


Title: Statemerging and generalising asymptotic entanglement of assistance Abstract: I will discuss the HorodeckiOppenheimWinter statemerging 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 singlecopy "random distillation". (This talk overlaps with my earlier seminar on this subject).


Title: Errorcorrecting oneway quantum computation Abstract: We present an approach to oneway quantum computation (1WQC) that can compensate for singlequbit errors, by encoding the logical information residing on physical qubits into fivequbit errorcorrecting code states. A logical twoqubit 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 twoqubit state and a logical fourqubit 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 twodimensional lattices for which entangling gates are generically global operations, such as atoms in optical lattices, quantum dots, or superconducting qubits.


Posters 

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.


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.


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


Title: Relative parameter estimation of quantum states subject to a global superselection 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.

