Speaker: Masahide Sasaki (National Institute of Information and Communications Technology)

Title: Going beyond Gaussian limits on continuous variable processing and measurement

The amplitude and phase quadratures of optical field, the so called continuous variables (CVs), play major roles both in photonic- and quantum-information and communications technology (P- and Q-ICT, respectively). Gaussian states, typically coherent states, and Gaussian operations on CVs serve as a complete basis for P-ICT. They are, however, only a part of the full potential of optical fields. Q-ICT provides a new paradigm to overcome the limits of P-ICT and to realize the quantum-limited measurement and the ultimate capacity of optical channels. Recent theories revealed that higher order operations beyond a fully Gaussian setting, namely non-Gaussian operations on CVs, are essentially required to realize the Q-ICT paradigm. We present recent advances of non-Gaussian operations and measurements to overcome the Gaussian limits. We first present latest results on non-Gaussian state generation and manipulation using photon counting and squeezed states, and then present an implementation of quantum receiver with a photon number resolving detector.

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Speaker: Lucien Hardy (Perimeter Institute)

Title: Operational Computation with Quantum Stuff

We imagine that we have a supply of stuff that, we suppose, has quantum properties that are not well known. We consider a computational scheme in which we attach inputs and outputs to this stuff to assist a computation (which can be classical). We consider how we might go about operationally characterizing the stuff to enable effective quantum computation.

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Speaker: Christopher A. Fuchs (Perimeter Institute for Theoretical Physics)

Title: Quantum-Bayesian Coherence

Coauthors: Christopher A. Fuchs and Ruediger Schack

In the quantum-Bayesian development of quantum mechanics, the Born Rule cannot be interpreted as a rule for setting measurement-outcome probabilities from an objective quantum state. But if not, what is the role of the rule? In this paper, we argue that it should be seen as an empirical addition to Bayesian reasoning itself. Particularly, we show how to view the Born Rule as a normative rule in addition to usual Dutch-book coherence. It is a rule that takes into account how one should assign probabilities to the consequences of various intended measurements on a physical system, but explicitly in terms of prior probabilities for and conditional probabilities consequent upon the imagined outcomes of a special counterfactual reference measurement. This interpretation is seen particularly clearly by representing quantum states in terms of probabilities for the outcomes of a fixed, fiducial symmetric informationally complete (SIC) measurement. We further explore the extent to which the general form of the new normative rule implies the full state-space structure of quantum mechanics. It seems to get quite far

Paper reference: arXiv:0906.2187v1 [quant-ph]

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Speaker: Félix Bussières (École Polytechnique de Montréal and University of Calgary)

Title: Flipping quantum coins

Coauthors: Guido Berlín, Gilles Brassard, Nicolas Godbout, Joshua A. Slater, Wolfgang Tittel

Coin flipping is a cryptographic primitive in which two distrustful parties wish to generate a random bit in order to choose between two alternatives. This task is impossible to realize when it relies solely on the asynchronous exchange of classical bits: one dishonest player has complete control over the final outcome. It is only when coin flipping is supplemented with quantum communication that this problem can be alleviated although partial bias remains. Unfortunately, practical systems are subject to loss of quantum data, which allows a cheater to force a bias that is complete or arbitrarily close to complete in all previous protocols. We report herein on the first implementation of a quantum coin-flipping protocol that is impervious to loss. Moreover, in the presence of unavoidable experimental noise, we propose to use this protocol sequentially to implement many coin flips, which guarantees that a cheater unwillingly reveals asymptotically, through an increased error rate, how many outcomes have been fixed. Hence, we demonstrate for the first time the possibility of flipping coins in a realistic setting.

Paper reference: http://arxiv.org/abs/0904.3946

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Speaker: Bryan Sanctuary (McGill University)

Title: The structure of spin

There are a number of experiments on particles with spin that quantum mechanics cannot explain. These include the double slit experiment and coincidence experiments using photons. It is proposed that intrinsic spin angular momentum has a two dimension structure and this leads to a new angular momentum state of magnitude 1/sqrt(2).

In order to form this new spin state it is necessary to relax the hermitian postulate of quantum mechanics and admit non-hermitian states, which is manifest as a quantum phase. However for both isolated and entangled spins, hermitian states naturally result.