Talks

10657 - 10668 of 16661 Results

What's an unknown POVM, and what does a two qubit state look like?

Matthew Pusey University of York

November 06, 2012

PIRSA:12110068
Holomorphic Blocks in 3d

Tudor Dimofte University of Edinburgh

November 06, 2012

PIRSA:12110056

Quantum Fields and Strings
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark

November 06, 2012

PIRSA:12110040

Cosmology
Penrose inequalities and the stability of non-uniform black strings

Pau Figueras Queen Mary University of London

November 01, 2012

PIRSA:12110039
What is a Wavefunction?

Wayne Myrvold Western University

November 01, 2012

PIRSA:12110060
An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132
Fault tolerance of "bad" quantum low-density parity check codes

Alexey Kovalev University of California, Riverside

October 29, 2012

PIRSA:12100130
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi Stanford University

October 26, 2012

PIRSA:12100051

Condensed Matter
Condensed Matter - Lecture 14

Assa Auerbach Technion – Israel Institute of Technology

October 26, 2012

PIRSA:12100039

Condensed Matter
Quantum Field Theory - Lecture 14B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 26, 2012

PIRSA:12100075

Quantum Fields and Strings
Quantum Field Theory - Lecture 14A

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 26, 2012

PIRSA:12100021

Quantum Fields and Strings
Effective field theory framework in QG

Xavier Calmet University of Sussex

Roberto Percacci SISSA International School for Advanced Studies

Astrid Eichhorn Universität Heidelberg

Martin Reuter Johannes Gutenberg University Mainz

October 25, 2012

PIRSA:12100121

Quantum Gravity

What's an unknown POVM, and what does a two qubit state look like?

Matthew Pusey University of York

November 06, 2012

PIRSA:12110068

If probabilities represent knowledge, what is an "unknown
probability"? De Finetti's theorem licenses the view that it is simply a
convenient metaphor for a certain class of knowledge about a series of
events. There are quantum versions for "unknown states" and "unknown
channels". I will explain how "unknown measurements" can be rehabilitated
too.

I will then move to a totally different topic. The Bloch sphere is handy
for representing qubit states, but the equivalent for two qubits is
15-dimensional! I will advocate instead drawing the set of states that Bob
can steer Alice to, the "steering ellipsoid". I will show how entanglement
and discord look from this perspective, and outline a geometric
classification of separable two qubit states.
Holomorphic Blocks in 3d

Tudor Dimofte University of Edinburgh

November 06, 2012

PIRSA:12110056

Quantum Fields and Strings

Recently techniques have been developed to compute the partition functions of 3d theories with N=2 supersymmetry on curved, compact spaces, in particular S^3 and S^2xS^1 (the latter giving a supersymmetric index). I will discuss how both of these partition functions can be decomposed as products of more fundamental, universal "holomorphic blocks." For 3d gauge theories arising from (auxiliary) 3-manifolds M, these holomorphic blocks are specific Chern-Simons partition functions on M.
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark

November 06, 2012

PIRSA:12110040

Cosmology

There are indications of a lower bound on magnetic fields in the intergalactic media. Since magnetic fields on such large scales are difficult to generate in the late universe, this might point to inflationary magnetogenesis as the origin of intergalactic magnetic fields. If the magnetic fields are generated during inflation, they are naturally correlated with the inflaton perturbations in a general class of models. This leads to a consistency relation between the power spectrum of primordial magnetic fields and the non-Gaussian three-point cross-correlation of magnetic fields with the inflaton perturbation. The size of non-Gaussianity can be expressed in a new magnetic non-linearity parameter b_NL. In the flattened shape where the non-Gaussianity is maximal, b_NL can be as large as 5000.
Penrose inequalities and the stability of non-uniform black strings

Pau Figueras Queen Mary University of London

November 01, 2012

PIRSA:12110039

In this talk I will first review static black holes in Kaluza-Klein theory. It is well-known that within this theory there exist black strings which are non-uniform along the Kaluza-Klein circle. Using numerical methods, I will explain how to construct (for the first time) non-uniform black strings in D>10, where D is the total number of spacetime dimensions. The stability of such black objects has not been discussed before, and in the last part of the talk I will explain how one can study the stability of non-uniform black strings using Penrose inequalities. This will lead to a new conjecture for the phase diagram of static Kaluza-Klein black holes.
What is a Wavefunction?

Wayne Myrvold Western University

November 01, 2012

PIRSA:12110060

The fact that the quantum wavefunction of a many-particle system is a function on a high-dimensional configuration space, rather than on spacetime, has led some to suggest that any realist understanding of quantum mechanics must regard configuration space as more fundamental than spacetime. Worse, it seems that a wavefunction monist ontology cannot help itself to talk of "configuration space" at all, without particles for the configurations to be configurations of. The wavefunction, it might seem, threatens to become a function defined on a high-dimensional space whose relation to spacetime is obscure. I will argue that such worries are misplaced.
An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132

Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Fault tolerance of "bad" quantum low-density parity check codes

Alexey Kovalev University of California, Riverside

October 29, 2012

PIRSA:12100130

In my talk, I will discuss various families of quantum low-density parity check (LDPC) codes and their fault tolerance. Such codes yield finite code rates and at the same time simplify error correction and encoding due to low-weight stabilizer generators. As an example, a large family of hypergraph-product codes is considered. Of particular interest are families of quantum LDPC codes with finite rate and distance scaling as square root of blocklength since this represents the best known exponent in distance scaling, even for codes of dimensionality 1. In relation to such codes, we show that any family of LDPC codes, quantum or classical, where distance scales as a positive power of the block length, $d \propto n^\alpha$, $\alpha>0$ ($\alpha<1$ for "bad" codes), can correct all errors with certainty if the error rate per qubit is sufficiently small. We specifically analyze the case of LDPC version of the quantum hypergraph-product codes recently suggested by Tillich and Z\'emor. These codes are a finite-rate generalization of the toric codes, and, for sufficiently large quantum computers, offer an advantage over the toric codes.
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi Stanford University

October 26, 2012

PIRSA:12100051

Condensed Matter

An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field, which are called fractional Chern insulators. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations become non-Abelian defects which create "worm holes" connecting the effective layers, and effectively change the topology of the space. Such topology-changing defects, which we name as "genons", can also be defined in other physical systems. We develop methods to compute the projective non-abelian braiding statistics of the genons, and we find the braiding is given by adiabatic modular transformations, or Dehn twists, of the topological state on the effective genus g surface. We find situations where the > genons have quantum dimension 2 and can be used for universal topological quantum computing (TQC), while the host topological state is by itself non-universal for TQC.
Condensed Matter - Lecture 14

Assa Auerbach Technion – Israel Institute of Technology

October 26, 2012

PIRSA:12100039

Condensed Matter
Quantum Field Theory - Lecture 14B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 26, 2012

PIRSA:12100075

Quantum Fields and Strings
Quantum Field Theory - Lecture 14A

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 26, 2012

PIRSA:12100021

Quantum Fields and Strings
Effective field theory framework in QG

Xavier Calmet University of Sussex

Roberto Percacci SISSA International School for Advanced Studies

Astrid Eichhorn Universität Heidelberg

Martin Reuter Johannes Gutenberg University Mainz

October 25, 2012

PIRSA:12100121

Quantum Gravity

Gravity Induced Grand Unification
Motivated by the lack of evidence for physics beyond the Standard Model in the TeV region, we discussed an alternative path for grand unification. We show that simple grand unification models based on e.g. SU(5) can work successfully even without low scale supersymmetry. In particular quantum gravitational effects could easily modify the unification conditions for the gauge and Yukawa couplings.
_____________________________

Testing the consistency of quantum gravity with low-energy properties of the standard model
Testing quantum gravity is possible by using, e.g. the available data on the properties of the standard model. I will discuss how a parameterisation of quantum gravity fluctuations in terms of metric fluctuations can be used to test the compatibility of quantum gravity with the observed low-energy properties of the standard model, such as the existence of fermions with masses much below the Planck mass.
______________________________

The Asymptotic Safety program
The effective average action approach to Quantum Einstein Gravity (QEG) is discussed as a natural framework for exploring the scale dependent Riemannian geometry and multifractal micro-structure of the effective spacetimes predicted by QEG. Their fractal properties are related to the functional RG flow on theory space, and the special role of the running cosmological constant is emphasized. The prospects of an experimental verification will also be discussed.

Title	Date	Collection	Type	Info
What's an unknown POVM, and what does a two qubit state look like?	2012‑11‑06	Quantum Foundations	Scientific Series	View details
Holomorphic Blocks in 3d	2012‑11‑06	Quantum Fields and Strings	Scientific Series	View details
Primordial Magnetic Fields & Non-Gaussianity	2012‑11‑06	Cosmology and Gravitation	Scientific Series	View details
Penrose inequalities and the stability of non-uniform black strings	2012‑11‑01	Strong Gravity	Scientific Series	View details
What is a Wavefunction?	2012‑11‑01	Quantum Foundations	Scientific Series	View details
An Informal Discussion About Topological Gauge Theory, part 2	2012‑10‑30	Quantum Matter	Other	View details
Fault tolerance of "bad" quantum low-density parity check codes	2012‑10‑29	Perimeter Institute Quantum Discussions	Scientific Series	View details
Synthetic non-Abelian anyons in fractional Chern insulators and beyond	2012‑10‑26	Quantum Matter	Scientific Series	View details
Condensed Matter - Lecture 14	2012‑10‑26	12/13 PSI - Condensed Matter	Course	View details
Quantum Field Theory - Lecture 14B	2012‑10‑26	12/13 PSI - Quantum Field Theory 1	Course	View details
Quantum Field Theory - Lecture 14A	2012‑10‑26	12/13 PSI - Quantum Field Theory 1	Course	View details
Effective field theory framework in QG	2012‑10‑25	Experimental Search for Quantum Gravity 2012	Conference	View details

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