Scientific Series

Displaying 3145 - 3156 of 5012

Quantum Raychaudhuri equation

Saurya Das
University of Lethbridge
February 20, 2014

PIRSA:14020130
Quantum Gravity
The Sherrington-Kirkpatrick model and its diluted version

Dmitry Panchenko
Texas A&M University
February 20, 2014

PIRSA:14020151
Mathematical physics
Causality, holography, and entanglement entropy
February 20, 2014

PIRSA:14020146
Quantum Gravity

Quantum Fields and Strings

Condensed Matter

Strong Gravity
The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng
California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter
Non equilibrium thermodynamic of gravitational screens

Laurent Freidel
Perimeter Institute for Theoretical Physics
February 19, 2014

PIRSA:14020144
Quantum Gravity

Mathematical physics
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states

Matthew Leifer
Chapman University
February 18, 2014

PIRSA:14020145
Quantum Foundations
Cluster Polylogarithms for Scattering Amplitudes
February 18, 2014

PIRSA:14020147
Quantum Fields and Strings
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento
Conestoga College
February 18, 2014

PIRSA:14020150
Cosmology
Probabilistic protocols in quantum information

Joshua Combes
University of Colorado Boulder
February 13, 2014

PIRSA:14020138
Quantum Information
Firewall evasion by quantum gravity

Ted Jacobson
University of Maryland, College Park
February 13, 2014

PIRSA:14020136
Quantum Gravity
On null singularities in general relativity

Mihalis Dafermos
Princeton University
February 13, 2014

PIRSA:14020133
Strong Gravity
Applications of Information Theory in Direct Sum and Direct Product Problems
February 12, 2014

PIRSA:14020142
Quantum Information

Quantum Raychaudhuri equation

Saurya Das
University of Lethbridge
February 20, 2014

PIRSA:14020130
Quantum Gravity
We compute quantum corrections to the Raychaudhuri equation, by replacing classical geodesics with quantal (Bohmian) trajectories, and show that they prevent focusing of geodesics, and the formation of conjugate points. We discuss implications for the Hawking-Penrose singularity theorems, and for curvature singularities. Reference: arXiv: 1311.6539
The Sherrington-Kirkpatrick model and its diluted version

Dmitry Panchenko
Texas A&M University
February 20, 2014

PIRSA:14020151
Mathematical physics
I will talk about two types of random processes -- the classical Sherrington-Kirkpatrick (SK) model of spin glasses and its diluted version. One of the main motivations in these models is to find a formula for the maximum of the process, or the free energy, in the limit when the size of the system is getting large. The answer depends on understanding the structure of the Gibbs measure in a certain sense, and this structure is expected to be described by the so called Parisi solution in the SK model and Mézard-Parisi solution in the diluted SK model. I will explain what these are and mention some results in this direction.
Causality, holography, and entanglement entropy
February 20, 2014

PIRSA:14020146
Quantum Gravity

Quantum Fields and Strings

Condensed Matter

Strong Gravity
After giving a brief overview of holographic entanglement entropy formulas, I will explore a curious feature they imply: when the bulk spacetime includes a black hole, the entanglement entropies often appear to depend on the spacetime geometry inside the horizon. I will ask whether this implies any loss of causality in the field theory. To answer this question, I will present a new general-relativity theorem concerning the causal structure of asymptotically AdS spacetimes, which implies an interesting relationship between bulk and boundary causal domains.
The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng
California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter
The quantum spin liquid is an emergent new state of matter, which has attracted a lot of recent attention. In particular, the time reversal symmetry broken spin liquid (Kalmeyer et. al. and Wen et. al.), characterized by the chiral ordering and fractionalized quasi-particle as a realization of the fractional quantum Hall state had been proposed for more than 20 years, but never identified as the true ground state in any more generic (e.g. Heisenberg spin exchange) models with time reversal symmetry. Here I will report two concrete examples where chiral spin liquid (CSL) emerge for a range of parameter space for kagome J1-J2-J3 (three nearest neighbors) model based on accurate density matrix renormalization group (DMRG) simulations. We identify long-range chiral ordering, ground state degeneracy, characteristic entanglement spectra, and the fractionalized topological Chern number to establish the topological state in such a system as the long-sought CSL. We further explicitly extract the modular matrix, which captures all the information of the fractional statistics of the quasi-particles in the system. I will also discuss the close relation of our model to some frustrated kagome antiferromagnets, and make a conjecture that J1 kagome model is near an unconventional critical point. I will conclude the talk with some discussions of the open directions.
Non equilibrium thermodynamic of gravitational screens

Laurent Freidel
Perimeter Institute for Theoretical Physics
February 19, 2014

PIRSA:14020144
Quantum Gravity

Mathematical physics
In this talk I will review the evidence for a mysterious and deep relationship between gravitational dynamics and thermodynamics. I will show how we can extend this connection to non equilibrium thermodynamics. Using the fact that the gravitational equations are fundamentally holographic, we express them in a way that shows a deep connection between gravity and the dynamics of viscous bubbles. We will explore some aspects of this surprising correspondence.
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states

Matthew Leifer
Chapman University
February 18, 2014

PIRSA:14020145
Quantum Foundations
The status of the quantum state is perhaps the most controversial issue in the foundations of quantum theory. Is it an epistemic state (representing knowledge, information, or belief) or an ontic state (a direct reflection of reality)? In the ontological models framework, quantum states correspond to probability measures over more fundamental states of reality. The quantum state is then ontic if every pair of pure states corresponds to a pair of measures that do not overlap, and is otherwise epistemic. Recently, several authors have derived theorems that aim to show that the quantum state must be ontic in this framework. Each of these theorems involve auxiliary assumptions of varying degrees of plausibility. Without such assumptions, it has been shown that models exist in which the quantum state is epistemic. However, the definition of an epistemic quantum state used in these works is extremely permissive. Only two quantum states need correspond to overlapping measures and furthermore the amount of overlap may be arbitrarily small. In order to provide an explanation of quantum phenomena such as no-cloning and the indistinguishability of pure states, the amount of overlap should be comparable to the inner product of the quantum states. In this talk, I show, without making auxiliary assumptions, that the ratio of overlap to inner product must go to zero exponentially in Hilbert space dimension for some families of states. This is done by connecting the overlap to Kochen-Specker noncontextuality, from which we infer that any contextuality inequality gives a bound on the ratio of overlap to inner product.
Cluster Polylogarithms for Scattering Amplitudes
February 18, 2014

PIRSA:14020147
Quantum Fields and Strings
Motivated by the cluster structure of two-loop scattering amplitudes in N = 4 Yang-Mills theory we define cluster polylogarithm functions. We find that all such functions of weight 4 are made up of a single simple building block associated to the A2 cluster algebra. Adding the requirement of locality on generalized Stasheff polytopes, we find that these A2 building blocks arrange themselves to form a unique function associated to the A3 cluster algebra. ThisA3 function manifests all of the cluster algebraic structure of the two-loop n-particle MHV amplitudes for all n, and we use it to provide an explicit representation for the most complicated part of the n = 7 amplitude as an example.
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento
Conestoga College
February 18, 2014

PIRSA:14020150
Cosmology
Systems which contemplate the gravitational interaction between compact objects and the matter content in a cosmological environment constitute an important problem which has been studied since the early days of General Relativity. The generalized McVittie black hole is a simple exact solution to this problem, which provides us with insight on some of its known physical aspects, as well as hints to new mechanisms which arise from a formal treatment. We review some properties of this solution and its matter source, which can be interpreted as a classical fluid but is also an exact solution to a nontrivial scalar field theory.
Probabilistic protocols in quantum information

Joshua Combes
University of Colorado Boulder
February 13, 2014

PIRSA:14020138
Quantum Information
Probabilistic protocols in quantum information are an attempt to improve performance by occasionally reporting a better result than could be expected from a deterministic protocol. Here we show that probabilistic protocols can never improve performance beyond the quantum limits on the corresponding deterministic protocol. To illustrate this result we examine three common probabilistic protocols: probabilistic amplification, weak value amplification, and probabilistic metrology. In each of these protocols we show explicitly that the optimal deterministic protocol is better than the corresponding probabilistic protocol when the probabilistic nature of the protocol is correctly accounted for.
Firewall evasion by quantum gravity

Ted Jacobson
University of Maryland, College Park
February 13, 2014

PIRSA:14020136
Quantum Gravity
It has been argued that if black hole evaporation is a unitary quantum process, then a black hole horizon must be cloaked by a "firewall", i.e. a highly excited state of local quantum fields. This reasoning is based on factorizing the Hilbert space into interior and exterior degrees of freedom. Such factorization ignores the Wheeler-deWitt constraint equation, which arises from the diffeomorphism invariance of quantum gravity. I will argue that this constraint evades the firewall.
On null singularities in general relativity

Mihalis Dafermos
Princeton University
February 13, 2014

PIRSA:14020133
Strong Gravity
This talk will discuss the formation, structure and interaction of null singularities for
the Einstein equations, as well as what this all means for the singular boundary
of generic space times within black hole regions.
Applications of Information Theory in Direct Sum and Direct Product Problems
February 12, 2014

PIRSA:14020142
Quantum Information
A fundamental question in complexity theory is how much resource is needed to solve k independent instances of a problem compared to the resource required to solve one instance. Suppose solving one instance of a problem with probability of correctness p, we require c units of some resource in a given model of computation. A direct sum theorem states that in order to compute k independent instances of a problem, it requires k times units of the resource needed to compute one instance. A strong direct product theorem states that, with o(k • c) units of the resource, one can only compute all the k instances correctly with probability exponentially small in k. In this talk, I am going to present some of recent progress on direct sum and direct product theorems in the model of communication complexity and two-prover one-round games with information-theoretic approach. The talk is based on parts of my doctoral work.

Title	Speaker(s)	Date	Talk Type	Info link
Quantum Raychaudhuri equation	Saurya Das	2014-02-20	Scientific Series	View details
The Sherrington-Kirkpatrick model and its diluted version	Dmitry Panchenko	2014-02-20	Scientific Series	View details
Causality, holography, and entanglement entropy		2014-02-20	Scientific Series	View details
The emergent of the chiral spin liquid in kagome Heisenberg model	Dong-Ning Sheng	2014-02-20	Scientific Series	View details
Non equilibrium thermodynamic of gravitational screens	Laurent Freidel	2014-02-19	Scientific Series	View details
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states	Matthew Leifer	2014-02-18	Scientific Series	View details
Cluster Polylogarithms for Scattering Amplitudes		2014-02-18	Scientific Series	View details
Evolution of cosmological black holes: exact solutions, accretion and scalar fields	Daniel Guariento	2014-02-18	Scientific Series	View details
Probabilistic protocols in quantum information	Joshua Combes	2014-02-13	Scientific Series	View details
Firewall evasion by quantum gravity	Ted Jacobson	2014-02-13	Scientific Series	View details
On null singularities in general relativity	Mihalis Dafermos	2014-02-13	Scientific Series	View details
Applications of Information Theory in Direct Sum and Direct Product Problems		2014-02-12	Scientific Series	View details

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