Scientific Series

Displaying 3529 - 3540 of 5117

Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
A positive and local formalism for quantum theory

Robert Oeckl Universidad Nacional Autónoma De Mexico (UNAM)
February 05, 2013

PIRSA:13020125
Quantum Foundations
Time Crystals

Alfred Shapere University of Kentucky
February 05, 2013

PIRSA:13020121
Quantum Fields and Strings
Multifield Reheating and the Fate of the Primordial Observables

Ewan Tarrant University of Nottingham
February 05, 2013

PIRSA:13020123
Cosmology
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter
Random matrices, free probability and quantum information theory

Benoit Collins
January 31, 2013

PIRSA:13010115
Quantum Information
Searching for topological phases in transition metal oxide heterostructures

Ying Ran Boston College
January 31, 2013

PIRSA:13010113
Condensed Matter
Hidden Structure in Linguistics: The Organization of Sound Systems

Elan Dresher

January 30, 2013

PIRSA:13010017
How to Fall into a Black Hole

Herman Verlinde Princeton University
January 29, 2013

PIRSA:13010020
Quantum Fields and Strings
Cosmic Tides

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Cosmology
What is motion? What is time?

Flavio Mercati University of Naples Federico II
January 23, 2013

PIRSA:13010003
Quantum Gravity
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter

Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
We have used a recently proposed quantum Monte Carlo algorithm [1] to study spinons (emergent S = 1/2 excitations) in 2D Resonating-Valence-Bond (RVB) spin liquids and in a J-Q model hosting a Neel – Valence Bond Solid (VBS) phase transition at zero temperature [2]. We confirm that spinons are well defined quasi-particles with finite intrinsic size in the RVB spin liquid. The distance distribution between two spinons shows signatures of deconfinement.
However, at the Neel–VBS transition, we found that the size of a single spinon is significantly greater than the bound-state in VBS, which indicates that spinons are “soft” and shrink when bound state is formed. Both spinon size and confinement length diverge as the critical point is approached. We have also compared spinon statistics in J-Q model with bilayer Heisenberg model and 1D spin chain. We conclude that the spinon deconfinement is marginal in the lowest-energy state in the spin-1 sector, due to very weak attractive spinon interactions. Deconfinement in the vicinity of the critical point should occur at higher energies.
A positive and local formalism for quantum theory

Robert Oeckl Universidad Nacional Autónoma De Mexico (UNAM)
February 05, 2013

PIRSA:13020125
Quantum Foundations
The general boundary formulation (GBF) is an atemporal, but spacetime local formulation of quantum theory. Usually it is presented in terms of the amplitude formalism, which, in the presence of a background time, recovers the pure state formalism of the standard formulation of quantum theory. After reviewing the essentials of the amplitude formalism I will introduce a new "positive formalism", which recovers instead a mixed state formalism. This allows to define general quantum operations within the GBF and opens it to quantum information theory. Moreover, the transition to the positive formalism eliminates operationally irrelevant structure, making the extraction of measurement probabilities more direct. As a consequence, the probability interpretation takes on a remarkably simple and compelling form. I shall describe implications of the positive formalism, both for our understanding of quantum theory and for the practical formulation of quantum theories. I also observe a certain convergence with Lucien Hardy's operator tensor formulation of quantum theory, on which I hope to comment
Time Crystals

Alfred Shapere University of Kentucky
February 05, 2013

PIRSA:13020121
Quantum Fields and Strings
I consider a class of simple classical systems which exhibit motion in their lowest-energy states and thus spontaneously break time-translation symmetry. Their Lagrangians have nonstandard kinetic terms and their Hamiltonians are multivalued functions of momentum, yet they are perfectly consistent and amenable to quantization. Field theoretical generalizations of these systems may have applications in condensed matter physics and cosmology.
Multifield Reheating and the Fate of the Primordial Observables

Ewan Tarrant University of Nottingham
February 05, 2013

PIRSA:13020123
Cosmology
The presence of additional light fields during inflation can source isocurvature fluctuations, which can cause the curvature perturbation $\zeta$, and its statistics to evolve on superhorizon scales. I will demonstrate that if these fluctuations have not completely decayed before the onset of perturbative reheating, then primordial observables such as the level of non--Gaussianity can develop substantial reheating dependant corrections. I will argue that for inflationary models where an adiabatic condition is not reached before the relevant fields begin to decay, we must be careful in our interpretation of any observational constraints that place bounds on the statistics of $\zeta$.
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter
Two types of topological phases have attracted a lot of attention in condensed matter physics: symmetry protected topological(SPT) phases and topologically ordered phases. On the one hand, SPT phases are protected by given global symmetries while there is no topological order in the bulk. On the other hand, topologically ordered phases do not require symmetry and feature topological ground state degeneracy. In this talk, I present a classification of phases with both topological orders and global symmetries, equipped with local bosonic exactly solvable models. This classification, in some sense, organizes previous pieces of understandings on SPT phases, topological orders, symmetry fractionalizations, into a single framework. Solution of the exactly solvable models and measurable consequences will be discussed.
Random matrices, free probability and quantum information theory

Benoit Collins
January 31, 2013

PIRSA:13010115
Quantum Information
In quantum information theory, random techniques have proven to be very useful. For example, many questions related to the problem of the additivity of entropies of quantum channels rely on fine properties of concentration of measure. In this talk, I will show that very different techniques of random matrix theory can complement quite efficiently more classical random techniques. I will spend some time on discussing the Weingarten calculus approach, and the operator norm approach. Both techniques have been initially used in free probability theory, and I will give some new applications of these techniques to quantum information theory.
Searching for topological phases in transition metal oxide heterostructures

Ying Ran Boston College
January 31, 2013

PIRSA:13010113
Condensed Matter
In this talk I will present our recent investigations on possible topological phases in (111) heterostructures of transition metal oxide. These (111) heterstructures are promising systems to realize many 2D topological phases at high temperatures, even with strong correlations, which is hard to be achieved in conventional materials. Several examples will be discussed, including high-temperature quantum spin hall effect in LaAlO3/LaAuO3/LaAlO3 bilayer, correlation induced topological phases in LaAlO3/LaNiO3/LaAlO3 multilayer, nearly flat topological band with C=2 (C: Chern number) in SrIrO3 trilayer, and abelian/nonabelian fractional quantum hall effects in the absence of Landau levels (fractional Chern insulators). If time is allowed, I will also briefly introduce our work on classifying wavefunctions of fractional Chern/topological insulators.
Hidden Structure in Linguistics: The Organization of Sound Systems

Elan Dresher

January 30, 2013

PIRSA:13010017

I will discuss some basic notions in the theory of phonology (sound systems in language). The sounds of a language are generally assumed to be composed of smaller constituents, called features. The features that make up a sound cannot be directly obtained from its pronunciation, but rather must be inferred from the system of contrasts that are at play in a particular language. How to determine which features are contrastive presents a logical and empirical puzzle that may be interesting to students of physics, who are accustomed to explaining observable events in terms of hidden structures that cannot be directly observed.
How to Fall into a Black Hole

Herman Verlinde Princeton University
January 29, 2013

PIRSA:13010020
Quantum Fields and Strings
In this talk I investigate the "firewall argument", that claims that black hole horizons can not be smooth. Using a holographic model of the black hole horizon as a quantum mechanical membrane, I show how to recover the black hole interior as an emergent smooth region of space-time. The reconstruction makes use of the formalism of quantum error correcting codes. I explain why the horizon of very old black holes appears to be singular, and formulate a complementarity principle that resolves this firewall paradox.
Cosmic Tides

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Cosmology
We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses and reconstruction of radial modes lost in 21 cm intensity mapping, which are essential for CMB and other cross correlations. We relate the tidal fields to the squeezed limit bispectrum, and present initial results from simulations and data from the SDSS.
What is motion? What is time?

Flavio Mercati University of Naples Federico II
January 23, 2013

PIRSA:13010003
Quantum Gravity
I give an account of the Machian approach to dynamics, from Mach's critique of Newton to the work of Barbour, Bertotti, York and O'Murchadha, which culminated in the theory of Shape Dynamics, a new and original way of thinking about General Relativity. I conclude commenting on the present research lines in Shape Dynamics, and the opportunity it offers to solve the problem of time in quantum gravity.

Support for this colloquium is provided by The Templeton Frontiers Program.
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter
Using quantum Monte Carlo simulations, we investigate the finite-temperature phase diagram of hard-core bosons (XY model) in two- and three-dimensional square lattices. To determine the phase boundaries, we perform a finite-size scaling analysis of the condensate fraction and/or the superfluid stiffness. We then discuss how this diagrams can be measured in experiments with trapped ultracold gases, where the systems are inhomogeneous. For that, we introduce a method based on the measurement of the zero-momentum occupation, which is adequate for experiments dealing with both homogeneous and trapped systems. Finally, we provide an analytical argument that demonstrates that the Bose-Hubbard model does not exhibit ﬁnite-temperature BEC in two dimensions, provided that density remains finite across the entire system in the thermodynamic limit.

Title	Speaker(s)	Date	Talk Type	Info link
Looking for spinon deconfinement in two dimensions	Ying Tang	2013-02-05	Scientific Series	View details
A positive and local formalism for quantum theory	Robert Oeckl	2013-02-05	Scientific Series	View details
Time Crystals	Alfred Shapere	2013-02-05	Scientific Series	View details
Multifield Reheating and the Fate of the Primordial Observables	Ewan Tarrant	2013-02-05	Scientific Series	View details
A classification of symmetry enriched topological phases with exactly solvable models	Ying Ran	2013-02-01	Scientific Series	View details
Random matrices, free probability and quantum information theory	Benoit Collins	2013-01-31	Scientific Series	View details
Searching for topological phases in transition metal oxide heterostructures	Ying Ran	2013-01-31	Scientific Series	View details
Hidden Structure in Linguistics: The Organization of Sound Systems	Elan Dresher	2013-01-30	Scientific Series	View details
How to Fall into a Black Hole	Herman Verlinde	2013-01-29	Scientific Series	View details
Cosmic Tides	Ue-Li Pen	2013-01-29	Scientific Series	View details
What is motion? What is time?	Flavio Mercati	2013-01-23	Scientific Series	View details
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.	Juan Carrasquilla	2013-01-22	Scientific Series	View details

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