Scientific Series

Displaying 3613 - 3624 of 5085

Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
General Relativity & Quantum Cosmology
An introduction to quantum channels and their capacities

Graeme Smith Institute for Quantum Computing (IQC)
November 07, 2012

PIRSA:12110066
Quantum Physics
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
High Energy Physics
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

PIRSA:12110040
Astrophysics
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
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
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Adrienne Erickcek University of North Carolina at Chapel Hill
October 25, 2012

PIRSA:12100125
Astrophysics
Astrophysical Searches for Quantum Gravity Signals

Jonathan Granot University of Hertfordshire
October 24, 2012

PIRSA:12100058
General Relativity & Quantum Cosmology
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London
October 23, 2012

PIRSA:12100105
Quantum Physics

Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
General Relativity & Quantum Cosmology
We describe of the evaporation process as driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We show how from this setting the emergence of several conservative scenarios for the final stage of the evaporation process can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are shown to take place.
An introduction to quantum channels and their capacities

Graeme Smith Institute for Quantum Computing (IQC)
November 07, 2012

PIRSA:12110066
Quantum Physics
A quantum communication channel can be put to many uses: it can transmit classical information, private classical information, or quantum information. It can be used alone, with shared entanglement, or together with other channels. For each of these settings there is a capacity that quantifies a channel's fundamental potential for communication. In this introductory talk, I will discuss what we known about the various capacities of a quantum channel, including a discussion of synergies between different channels and related additivity questions.
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
High Energy Physics
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
Astrophysics
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.
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.
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Adrienne Erickcek University of North Carolina at Chapel Hill
October 25, 2012

PIRSA:12100125
Astrophysics
Chameleon gravity is a scalar-tensor theory that mimics general relativity in the Solar System. The scalar degree of freedom is hidden in high-density environments because the effective mass of the chameleon scalar depends on the trace of the stress-energy tensor. In the early Universe, when the trace of the stress-energy tensor is nearly zero, the chameleon is very light and Hubble friction prevents it from reaching its potential minimum. Whenever a particle species becomes non-relativistic, however, the trace of the stress-energy tensor is temporarily nonzero, and the chameleon begins to roll. I will show that these "kicks" to the chameleon field have catastrophic consequences for chameleon gravity. The velocity imparted to the chameleon is sufficiently large that the chameleon's mass changes rapidly as it slides past its potential minimum. This nonadiabatic process shatters the chameleon field by generating extremely high-energy perturbations, casting doubt on chameleon gravity's viability as an alternative to general relativity.
Astrophysical Searches for Quantum Gravity Signals

Jonathan Granot University of Hertfordshire
October 24, 2012

PIRSA:12100058
General Relativity & Quantum Cosmology
Some recent searches for quantum gravity signatures using observations of distant astrophysical sources will be discussed, focusing on the search for Lorentz invariance violation (LIV) in the form of a dependence of the photon propagation speed on its energy. Fermi gamma-ray space telescope observations of ~8 keV to ~30 GeV photons from a short (< 1 s) gamma-ray burst (GRB 090510) at a cosmological distance (z = 0.903), enabled for the first time to put a direct time of flight limit on a possible linear variation of the speed of light with photon energy that is beyond the Planck scale. Parameterizing |v/c-1| = E/E_{QG} our most conservative limits are E_{QG}/E_{Planck} > 1.2, while less conservative limits are up to 1-2 orders of magnitude stricter. Other types of astrophysical searches for LIV will be briefly outlined, along with some prospects for the future.
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London
October 23, 2012

PIRSA:12100105
Quantum Physics
I will discuss the central role of correlations in thermodynamic directionality, how strong correlations can distort the thermodynamic arrow and contrast these distortions in both the classical and quantum regimes. These distortions constitute non-linear entanglement witnesses, and give rise to a rich information-theoretic structure. I shall explain how these results are then cast into the language of fluctuation theorems to derive a generalized exchange fluctuation theorem, and discuss the limitations of such a framework.

Title	Speaker(s)	Date	Talk Type	Info link
Dynamical evaporation of quantum horizons		2012-11-08	Scientific Series	View details
An introduction to quantum channels and their capacities	Graeme Smith	2012-11-07	Scientific Series	View details
What's an unknown POVM, and what does a two qubit state look like?	Matthew Pusey	2012-11-06	Scientific Series	View details
Holomorphic Blocks in 3d	Tudor Dimofte	2012-11-06	Scientific Series	View details
Primordial Magnetic Fields & Non-Gaussianity	Martin Sloth	2012-11-06	Scientific Series	View details
Penrose inequalities and the stability of non-uniform black strings	Pau Figueras	2012-11-01	Scientific Series	View details
What is a Wavefunction?	Wayne Myrvold	2012-11-01	Scientific Series	View details
Fault tolerance of "bad" quantum low-density parity check codes	Alexey Kovalev	2012-10-29	Scientific Series	View details
Synthetic non-Abelian anyons in fractional Chern insulators and beyond	Xiaoliang Qi	2012-10-26	Scientific Series	View details
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity	Adrienne Erickcek	2012-10-25	Scientific Series	View details
Astrophysical Searches for Quantum Gravity Signals	Jonathan Granot	2012-10-24	Scientific Series	View details
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.	David Jennings	2012-10-23	Scientific Series	View details

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Format results

Dynamical evaporation of quantum horizons

An introduction to quantum channels and their capacities

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

Holomorphic Blocks in 3d

Primordial Magnetic Fields & Non-Gaussianity

Penrose inequalities and the stability of non-uniform black strings

What is a Wavefunction?

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

Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Astrophysical Searches for Quantum Gravity Signals

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

Dynamical evaporation of quantum horizons

An introduction to quantum channels and their capacities

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

Holomorphic Blocks in 3d

Primordial Magnetic Fields & Non-Gaussianity

Penrose inequalities and the stability of non-uniform black strings

What is a Wavefunction?

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

Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Astrophysical Searches for Quantum Gravity Signals

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.