Scientific Series

Displaying 3265 - 3276 of 5085

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
General Relativity & Quantum Cosmology

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 Physics
Cluster Polylogarithms for Scattering Amplitudes
February 18, 2014

PIRSA:14020147
High Energy Physics
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014

PIRSA:14020150
Astrophysics
Probabilistic protocols in quantum information

Joshua Combes University of Colorado Boulder
February 13, 2014

PIRSA:14020138
Quantum Physics
Firewall evasion by quantum gravity

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

PIRSA:14020136
General Relativity & Quantum Cosmology
On null singularities in general relativity

Mihalis Dafermos Princeton University
February 13, 2014

PIRSA:14020133
General Relativity & Quantum Cosmology
Applications of Information Theory in Direct Sum and Direct Product Problems
February 12, 2014

PIRSA:14020142
Quantum Physics
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics
Bosonic particle-correlated states

Zhang Jiang University of New Mexico
February 06, 2014

PIRSA:14020135
Quantum Physics
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014

PIRSA:14020087
General Relativity & Quantum Cosmology

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
General Relativity & Quantum Cosmology

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 Physics
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
High Energy Physics
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
Astrophysics
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 Physics
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
General Relativity & Quantum Cosmology
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
General Relativity & Quantum Cosmology
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 Physics
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.
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics
After a short introduction to open inflation and the observed large-scale cosmic microwave anomalies, which have been confirmed by the Planck satellite, I'll argue that the anomalies are naturally explained in the context of a marginally-open, negatively curved universe. I'll look in particular at the dipole power asymmetry, and motivate that this asymmetry can happen if our universe has bubble nucleated in a phase transition during a period of early inflation, and, as a result, has open geometry. Open inflation models, which are motivated by the string landscape and can excite `super-curvature' perturbation modes, can explain the presence of a very-large-scale perturbation, like the one we observe, which leads to a dipole modulation of the power spectrum. I'll provide a specific implementation of the scenario which is compatible with all existing constraints.
Bosonic particle-correlated states

Zhang Jiang University of New Mexico
February 06, 2014

PIRSA:14020135
Quantum Physics
Quantum many-body problems are notorious hard. This is partly because the Hilbert space becomes exponentially big with the particle number N. While exact solutions are often considered intractable, numerous approaches have been proposed using approximations. A common trait of these approaches is to use an ansatz such that the number of parameters either does not depend on N or is proportional to N, e.g., the matrix-product state for spin lattices, the BCS wave function for superconductivity, the Laughlin wave function for fractional quantum Hall effects, and the Gross-Pitaecskii theory for BECs. Among them the product ansatz for BECs has precisely predicted many useful properties of Bose gases at ultra-low temperature. As particle-particle correlation becomes important, however, it begins to fail. To capture the quantum correlations, we propose a new
set of states, which constitute a natural generalization of the product-state ansatz. Our state of N=d& times;n identical particles is derived by symmetrizing the n-fold product of a d-particle quantum state. For fixed d, the parameter space of our state does not grow with N. Numerically, we show that our ansatz gives the right description for the ground state and time evolution of the two-site Bose-Hubbard model.
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014

PIRSA:14020087
General Relativity & Quantum Cosmology
The equation of state of matter at and above nuclear densities remains a major theoretically uncertain prediction of QCD. Observations of the mass-radius relationship of neutron stars constrain, and can directly measure, the dense matter equation of state. I will discuss how measurements of neutron star radii have already constrained the dEOS, and how future work will directly measure the dEOS, providing an important constraint on models of the strong force.

Title	Speaker(s)	Date	Talk Type	Info link
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
Our Lopsided Universe	Marina Cortes	2014-02-11	Scientific Series	View details
Bosonic particle-correlated states	Zhang Jiang	2014-02-06	Scientific Series	View details
The Radius of Neutron Stars and the Dense Matter Equation of State	Robert Rutledge	2014-02-06	Scientific Series	View details

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The emergent of the chiral spin liquid in kagome Heisenberg model

Non equilibrium thermodynamic of gravitational screens

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

Cluster Polylogarithms for Scattering Amplitudes

Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Probabilistic protocols in quantum information

Firewall evasion by quantum gravity

On null singularities in general relativity

Applications of Information Theory in Direct Sum and Direct Product Problems

Our Lopsided Universe

Bosonic particle-correlated states

The Radius of Neutron Stars and the Dense Matter Equation of State

The emergent of the chiral spin liquid in kagome Heisenberg model

Non equilibrium thermodynamic of gravitational screens

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

Cluster Polylogarithms for Scattering Amplitudes

Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Probabilistic protocols in quantum information

Firewall evasion by quantum gravity

On null singularities in general relativity

Applications of Information Theory in Direct Sum and Direct Product Problems

Our Lopsided Universe

Bosonic particle-correlated states

The Radius of Neutron Stars and the Dense Matter Equation of State