Scientific Series

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Almost quantum correlations

Antonio Acin
Institute of Photonic Sciences (ICFO)

April 09, 2014

PIRSA:14040065
Beyond local causality: causation and correlation after Bell

Matthew Pusey
University of York
April 08, 2014

PIRSA:14040130
Quantum Foundations
Is the Milky Way Ringing?

Lawrence Widrow
Queen's University
April 08, 2014

PIRSA:14040137
Cosmology
The unitary Fermi gas across the superfluid transition

Olga Goulko
University of Massachusetts Amherst
April 04, 2014

PIRSA:14040119
Condensed Matter
Quantum Gravity, Trees, and Polynomials

Fabien Vignes-Tourneret
Université Claude Bernard Lyon 1
April 03, 2014

PIRSA:14040134
Quantum Gravity
Quantum Computing with Noninteracting Particles

Alex Arkhipov
Massachusetts Institute of Technology (MIT)
April 02, 2014

PIRSA:14040077
Quantum Information
Scribble, Scribble

Isabella Stefanescu

April 02, 2014

PIRSA:14040117
Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Abolhassan Vaezi
Cornell University
April 01, 2014

PIRSA:14040120
Condensed Matter
Incompatibility of observables in quantum theory and other probabilistic theories
April 01, 2014

PIRSA:14040075
Quantum Foundations
RG flows with N=1 supersymmetry

Henriette Elvang
University of Michigan–Ann Arbor
April 01, 2014

PIRSA:14030074
Quantum Fields and Strings
The not-so-homogeneous universe

Phil Bull
Queen Mary University of London
April 01, 2014

PIRSA:14040129
Cosmology
Effective field theory for hydrodynamical systems

Alberto Nicolis
Columbia University
March 28, 2014

PIRSA:14030121
Quantum Fields and Strings

Cosmology

Almost quantum correlations

Antonio Acin
Institute of Photonic Sciences (ICFO)

April 09, 2014

PIRSA:14040065

Quantum theory is successfully tested in any experimental lab every day. Apart from its experimental validity, quantum theory also constitutes a robust theoretical framework: small variations of its formalism often lead to highly implausible consequences, such as violation of the no-signalling principle or a significant increase of the computational power. In fact, it has been argued that quantum theory may represent an island in theory space. We show that, at the level of correlations, quantum theory may not be as special as initially thought. In order to do so, we define the set of almost quantum correlations and prove that this set is (i) strictly larger than the set of quantum correlations but (ii) satisfies most of the information principles introduced to characterize quantum correlations, such as local orthogonality, macroscopic locality, no advantage for nonlocal computation or non-trivial communication complexity. We also provide numerical evidence that the set is compatible with information causality. Finally, we briefly discuss how the set of almost quantum correlations naturally emerges in the consistent histories approach to quantum physics.
Beyond local causality: causation and correlation after Bell

Matthew Pusey
University of York
April 08, 2014

PIRSA:14040130
Quantum Foundations
There is now a remarkable mathematical theory of causation. But applying this theory to a Bell scenario implies the Bell inequalities, which are violated in experiment. We alleviate this tension by translating the basic definitions of the theory into the framework of generalised probabilistic theories. We find that a surprising number of results carry over: the d-separation criterion for conditional independence (the no-signalling principle on steroids), and even certain quantitative limits on correlations. Finally, we begin a classification of the causal structures, such as the Bell scenarios, that are "interesting" from this perspective. Joint work with Joe Henson and Raymond Lal.
Is the Milky Way Ringing?

Lawrence Widrow
Queen's University
April 08, 2014

PIRSA:14040137
Cosmology
Recent observations from three different astronomical surveys have revealed evidence for asymmetries about the Galactic midplane in the kinematics of solar neighborhood stars. These asymmetries appear, in part, as compression-rarefaction modes in the bulk motions of stars perpendicular to the midplane. I will discuss the hypothesis that these motions were caused by the recent passage of a satellite galaxy or dark matter subhalo through the Galactic disk. In short, we may be witnessing the early stages of a disk-heating event during which the Galaxy's disk relaxes to a new state after interacting with substructure from its own halo.
The unitary Fermi gas across the superfluid transition

Olga Goulko
University of Massachusetts Amherst
April 04, 2014

PIRSA:14040119
Condensed Matter
Quantum Monte Carlo is a versatile tool for studying strongly interacting theories in condensed matter physics from first principles. A prominent example is the unitary Fermi gas: a two-component system of fermions interacting with divergent scattering length. I will present numerical results for different properties of the homogeneous, spin-balanced unitary Fermi gas across the superfluid transition, such as the critical temperature, the equation of state and the temperature dependence of the contact density. Our values show good agreement with recent experimental data.
Quantum Gravity, Trees, and Polynomials

Fabien Vignes-Tourneret
Université Claude Bernard Lyon 1
April 03, 2014

PIRSA:14040134
Quantum Gravity
The perturbative series of colored group field theory are governed by a combinatorial 1/N-expansion. Controlling its coefficients is essential in order to understand the continuum limit. I will show how such a program is naturally related to higher-dimensional generalizations of trees in a colored Boulatov-Ooguri model, and present some partial results on the enumeration of such strucures in melonic graphs. This talk is mainly based on recent results by Baratin, Carrozza, Oriti, Ryan, and Smerlak ("Melonic phase transition in group field theory". arXiv: 1307.5026).
Quantum Computing with Noninteracting Particles

Alex Arkhipov
Massachusetts Institute of Technology (MIT)
April 02, 2014

PIRSA:14040077
Quantum Information
We introduce an abstract model of computation corresponding to an experiment in which identical, non-interacting bosons are sent through a non-adaptive linear circuit before being measured. We show that despite the very limited nature of the model, an exact classical simulation would imply a collapse of the polynomial hierarchy. Moreover, under plausible conjectures, a "noisy" approximate simulation would do the same. This gives evidence that quantum computers can sample a distribution that classical computers cannot even approximate, even when restricted to use no entanglement except that arising from particles being identical. We briefly discuss experimental prospects for realizing this model. This talk is based on The Computational Complexity of Linear Optics [STOC '11], which is joint work with Scott Aaronson.
Scribble, Scribble

Isabella Stefanescu

April 02, 2014

PIRSA:14040117

The live performance of a drawing contains information, expression and meaning that a finished drawing does not. Part performance, part demonstration, Isabella Stefanescu’s talk will explore the artistic challenges in creating performance pieces with the Euphonopen, an assemblage of hardware and software designed to map the characteristic mark making gestures of an artist to sound. Various stages of the Euphonopen project have been presented at SIGGRAPH (2010), Concordia University Live Electroacoustic Colloquium (2011), McGill University Time Forms Conference (2013).
Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Abolhassan Vaezi
Cornell University
April 01, 2014

PIRSA:14040120
Condensed Matter
The possibility of realizing non-Abelian statistics and utilizing it for topological quantum computation (TQC) has generated widespread interest. However, the non-Abelian statistics that can be realized in most accessible proposals is not powerful enough for universal TQC. In this talk, I consider a simple bilayer fractional quantum Hall (FQH) system with the 1/3 Laughlin state in each layer, in the presence of interlayer tunneling. I show that interlayer tunneling can drive a continuous phase transition to an exotic non-Abelian state that contains the famous `Fibonacci' anyon, whose non-Abelian statistics is powerful enough for universal TQC. The analysis that I will present towards this result rests on startling agreements from a variety of distinct methods, including thin torus limits, effective field theories, and coupled wire constructions.

Next, I discuss the experimental aspects of our proposal and potential probes for the Fibonacci phase. I show that the charge gap remains open at the phase transition while the neutral gap closes. This raises the question of whether these exotic phases may have already been realized at nu=2/3 in bilayers, as past experiments may not have definitively ruled them out. Finally, I will discuss about the generalizations to multi-layer states as well as the duality between the interlayer pairing and interlayer tunneling problems.

Reference: arXiv:1403.3383
Incompatibility of observables in quantum theory and other probabilistic theories
April 01, 2014

PIRSA:14040075
Quantum Foundations
We introduce a new way of quantifying the degrees of incompatibility of two observables in a probabilistic physical theory and, based on this, a global measure of the degree of incompatibility inherent in such theories. This opens up a flexible way of comparing probabilistic theories with respect to the nonclassical feature of incompatibility. We show that quantum theory contains observables that are as incompatible as any probabilistic physical theory can have. In particular, we prove that two of the most common pairs of complementary observables (position and momentum; number and phase) are maximally incompatible. However, if one adopts a more refined measure of the degree of incompatibility, for instance, by restricting the comparison to binary observables, it turns out that there are probabilistic theories whose inherent degree of incompatibility is greater than that of quantum theory. Finally, we analyze the noise tolerance of the incompatibility of a pair of observables in a CHSH-Bell experiment.
RG flows with N=1 supersymmetry

Henriette Elvang
University of Michigan–Ann Arbor
April 01, 2014

PIRSA:14030074
Quantum Fields and Strings
The dilaton effective action plays a key role for the recent proof of the a-theorem by Schwimmer and Komargodski. In the presence of other massless modes, one may ask if this proof is affected. In particular, in renormalization group (RG) flows with N=1 supersymmetry, there is a natural massless partner of the dilaton, namely an axion field. I will discuss RG flows, the a-theorem, and the form of the N=1 supersymmetric dilaton-axion effective action and its physics.
The not-so-homogeneous universe

Phil Bull
Queen Mary University of London
April 01, 2014

PIRSA:14040129
Cosmology
The assumption of spatial homogeneity lies at the heart of the concordance cosmological model. But as I will discuss, truly solid empirical evidence for global (statistical) homogeneity is lacking, and tricky theoretical issues abound. I review a few recent advances in understanding the role inhomogeneity plays in cosmology, including some unexpected effects on light propagation, the death (and rebirth) of backreaction, and impending observational annoyances related to the lumpy local Universe. I'll also talk about some near-future observations that can give us a handle on these effects
Effective field theory for hydrodynamical systems

Alberto Nicolis
Columbia University
March 28, 2014

PIRSA:14030121
Quantum Fields and Strings

Cosmology
I will review a recently proposed formalism that describes fluids and superfluids in effective field theory terms. I will then focus on applying this formalism to peculiar string-like objects that exist in fluid systems: vortex lines and vortex rings. These do not obey Newton's second law, and, as a consequence, their behavior is highly counterintuitive. I will describe how effective field theory provides us with an optimal tool to understand how they move and how they interact with one another and with sound.

Title	Speaker(s)	Date	Talk Type	Info link
Almost quantum correlations	Antonio Acin	2014-04-09	Scientific Series	View details
Beyond local causality: causation and correlation after Bell	Matthew Pusey	2014-04-08	Scientific Series	View details
Is the Milky Way Ringing?	Lawrence Widrow	2014-04-08	Scientific Series	View details
The unitary Fermi gas across the superfluid transition	Olga Goulko	2014-04-04	Scientific Series	View details
Quantum Gravity, Trees, and Polynomials	Fabien Vignes-Tourneret	2014-04-03	Scientific Series	View details
Quantum Computing with Noninteracting Particles	Alex Arkhipov	2014-04-02	Scientific Series	View details
Scribble, Scribble	Isabella Stefanescu	2014-04-02	Scientific Series	View details
Fibonacci Anyons From Abelian Bilayer Quantum Hall States	Abolhassan Vaezi	2014-04-01	Scientific Series	View details
Incompatibility of observables in quantum theory and other probabilistic theories		2014-04-01	Scientific Series	View details
RG flows with N=1 supersymmetry	Henriette Elvang	2014-04-01	Scientific Series	View details
The not-so-homogeneous universe	Phil Bull	2014-04-01	Scientific Series	View details
Effective field theory for hydrodynamical systems	Alberto Nicolis	2014-03-28	Scientific Series	View details

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