Talks

10537 - 10548 of 19186 Results

Uni10 Tensor Network Library

Ying-Jer Kao National Taiwan University

August 05, 2014

PIRSA:14080001

Condensed Matter
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)

July 31, 2014

PIRSA:14070033

General Relativity & Quantum Cosmology
Asymmetric Hawking Radiation : Baryogenesis from Hawking Radiation

Anson Hook University of Maryland, College Park

July 29, 2014

PIRSA:14070019

High Energy Physics
Discussion with Neil Turok

Neil Turok University of Edinburgh

July 24, 2014

PIRSA:14070029
Space-Time Circuit-to-Hamiltonian construction and Its Applications

Barbara Terhal Delft University of Technology

July 23, 2014

PIRSA:14070031

Quantum Physics
What’s Interesting These Days (With Gravity)?

Latham Boyle University of Edinburgh

July 23, 2014

PIRSA:14070028
Supersymmetric AdS5 solutions in M-theory and Class S SCFT's

Ibrahima Bah University of Southern California (USC)

July 22, 2014

PIRSA:14070032

High Energy Physics
Life as a Physicist

Natalia Toro Stanford University

Philip Schuster Stanford University

July 22, 2014

PIRSA:14070027
Can Quantum Correlations be Explained Causally?

Robert Spekkens Perimeter Institute for Theoretical Physics

July 21, 2014

PIRSA:14070026
Inferring causal structure: a quantum advantage

Katja Ried Universität Innsbruck

July 17, 2014

PIRSA:14070021

Quantum Physics
Spatially coupled quantum LDPC codes

Jean-Pierre Tillich

July 16, 2014

PIRSA:14070015
Measuring the overhead of a quantum error correcting code

Austin Fowler Institute for Quantum Computing (IQC)

July 16, 2014

PIRSA:14070014

Uni10 Tensor Network Library

Ying-Jer Kao National Taiwan University

August 05, 2014

PIRSA:14080001

Condensed Matter
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)

July 31, 2014

PIRSA:14070033

General Relativity & Quantum Cosmology

The authors have revealed a fundamental structure which has been hidden within the Wheeler-DeWitt (WDW) constraint of four dimensional General Relativity (GR) of Lorentzian signature in the Ashtekar self-dual variables. The WDW equation can be written as the commutator of two geometric entities, namely the imaginary part of the Chern-Simons functional Q and the local volume element V(x) of 3-space. Upon quantization with cosmological constant, the WDW equation takes on the form of the Lie algebra of the affine group of transformations of the straight line, with Q and V(x) playing the role of the generators for the Lie algebra. The generators are Hermitian, which addresses the issue of the implementation of the reality conditions of GR at the quantum level. Additionally, the irreducible unitary representations (IUR) implement the positivity of the spectrum of the volume operator V(x) at the quantum level This development has led to the existence of elements of the physical Hilbert space for four dimensional gravity of Lorentzian signature, the full theory, in the form of irreducible, unitary representations of the affine group of transformations of the straight line. The affine Lie algebraic structure of the WDW equation remains intact even in the presence of nongravitational fields. This feature has led to the extension of the affine group formulation to elements of the physical Hilbert space for gravity coupled to the full Standard Model of particle physics, quantized on equal footing. Work on the physical interpretation of the states with respect to gauge-diffeomorphism invariant observables, and spacetime geometries solving the Einstein equations is in progress. The journal reference for these results are as follows: - The first result has been published in CQG 30 (2013) 065013 - The second result has just been published in Annals of Physics Journal Vol.343, pages 153-163, April 2014
Asymmetric Hawking Radiation : Baryogenesis from Hawking Radiation

Anson Hook University of Maryland, College Park

July 29, 2014

PIRSA:14070019

High Energy Physics

We show that in the presence of a chemical potential, black hole evaporation generates baryon number. If the inflaton or Ricci scalar is derivatively coupled to the B-L current, the expansion of the universe acts as a chemical potential and splits the energy levels of particles and their anti-particles. The asymmetric Hawking radiation of primordial black holes can thus be used to generate a B-L asymmetry. If dark matter is produced by the same mechanism, the coincidence between the mass density of visible and dark matter can be naturally explained.
Discussion with Neil Turok

Neil Turok University of Edinburgh

July 24, 2014

PIRSA:14070029
Space-Time Circuit-to-Hamiltonian construction and Its Applications

Barbara Terhal Delft University of Technology

July 23, 2014

PIRSA:14070031

Quantum Physics

The circuit-to-Hamiltonian construction translates a dynamics (a quantum circuit and its output) into statics (the groundstate of a circuit Hamiltonian) by explicitly defining a quantum register for a clock. The standard Feynman-Kitaev construction uses one global clock for all qubits while we consider a different construction in which a clock is assigned to each point in space where a qubit of the quantum circuit resides. We show how one can apply this construction to one-dimensional quantum circuits for which the circuit Hamiltonian realizes the dynamics of a vibrating string. We discuss how the construction can be used (1) in quantum complexity theory to obtain new and stronger results in QMA and (2) how one can realize, based on this construction, universal quantum adiabatic computation and a universal quantum walk using a 2D interacting particle Hamiltonian. See http://arxiv.org/abs/1311.6101
What’s Interesting These Days (With Gravity)?

Latham Boyle University of Edinburgh

July 23, 2014

PIRSA:14070028

Many of the most interesting open issues in physics today are related in one way or another to gravity. For the past 100 years, we have described spacetime and gravity via Einstein's theory of "General Relativity." But when we try to mesh General Relativity with the rest of physics, and use it to describe the cosmos, we encounter a range of puzzles. I'll describe some of these puzzles, and some routes to attacking them that look exciting to me.
Supersymmetric AdS5 solutions in M-theory and Class S SCFT's

Ibrahima Bah University of Southern California (USC)

July 22, 2014

PIRSA:14070032

High Energy Physics

We provide a framework for describing gravity duals of four-dimensional N=1 superconformal field theories obtained by compactifying a stack of M5-branes on a Riemann surface. The gravity solutions are completely specified by two scalar potentials whose pole structures on the Riemann surface correspond to the spectrum of punctures that labels different theories. We discuss how to identify these puncture in gravity.
Life as a Physicist

Natalia Toro Stanford University

Philip Schuster Stanford University

July 22, 2014

PIRSA:14070027

Ever wonder what a day in the life of a theoretical physicist is like?, Life as a Physicist is an opportunity to ask questions of two Perimeter Institute Faculty members.
Can Quantum Correlations be Explained Causally?

Robert Spekkens Perimeter Institute for Theoretical Physics

July 21, 2014

PIRSA:14070026

There is a strong correlation between the sun rising and the rooster crowing, but to say that the one causes the other is to say more. In particular, it says that making the rooster crow early will not precipitate an early dawn, whereas making the sun rise early (for instance, by moving the rooster eastward) can lead to some early crowing. Intervening upon the natural course of events in this manner is a good way of discovering causal relations. Sometimes, however, we can't intervene, or we'd prefer not to. For instance, in trying to determine whether smoking causes lung cancer, we'd prefer not to force any would-be nonsmokers to smoke. Fortunately, there are some clever tricks that allow us to extract information about what causes what entirely from features of the observed correlations. One of these tricks was discovered by the physicist John Bell in 1964. In a groundbreaking paper, he used it to demonstrate the seeming impossibility of providing a causal explanation of certain quantum correlations. This revealed a fundamental tension between quantum theory and Einstein's theory of relativity --the two central pillars of modern physics. It is a tension that is still with us today.
Inferring causal structure: a quantum advantage

Katja Ried Universität Innsbruck

July 17, 2014

PIRSA:14070021

Quantum Physics

A fundamental question in trying to understand the world -- be it classical or quantum -- is why things happen. We seek a causal account of events, and merely noting correlations between them does not provide a satisfactory answer. Classical statistics provides a better alternative: the framework of causal models proved itself a powerful tool for studying causal relations in a range of disciplines. We aim to adapt this formalism to allow for quantum variables and in the process discover a new perspective on how causality is different in the quantum world. Causal inference is a central task in the context of causal models: given observed statistics over a set of variables, one aims to infer how they are causally related. Yet in the seemingly simple case of just two classical variables, this is impossible (unless one makes additional assumptions). I will show how the analogous task for quantum variables can be solved. This quantum advantage is reminiscent of the advantages that quantum mechanics offers in computing and communication, and may lead to similarly rich insights. Our scheme is corroborated by data obtained in collaboration with Kevin Resch's experimental group. Time permitting, I will also address other applications of the quantum causal models. arXiv:1406.5036
Spatially coupled quantum LDPC codes

Jean-Pierre Tillich

July 16, 2014

PIRSA:14070015

Spatially coupled LDPC were introduced by Felström and Zigangirov in 1999. They might be viewed in the following way, take several several instances of a certain LDPC code family, arrange them in a row and then mix the edges of the codes randomly among neighboring layers. Moreover fix the bits of the first and last layers to zero. It has soon been found out that iterative decoding behaves much better for this code than for the original LDPC code. A breakthrough occurred when it was proved by Kudekar, Richardson and Urbanke that these codes attain the capacity of all binary input memoryless output-symmetric channels.

All these nice features of classical spatially coupled LDPC codes suggest to study whether they have a quantum analogue. The fact that spatially coupled LDPC codes may afford to have large degrees and still perform well under iterative decoding would be quite interesting in the quantum setting, since by the very nature of the quantum construction of stabilizer codes the rows of the parity-check matrix of the quantum code have to belong to the code which is decoded by the iterative decoder. This implies that we should have rather large row weights to avoid severe error-floor phenomena and/or oscillatory behavior of iterative decoding which degrades significantly its performance.

With Andriyanova and Maurice, I showed last year that it is possible to come up with coupled versions of quantum LDPC codes that perform excellently under iterative decoding. For instance we have constructed a spatially coupled LDPC code family of rate $\approx \frac{1}{4}$ which performs well under iterative decoding even for noise values close to the hashing bound $p \approx 0.127$.
This represents a tremendous improvement over all previous known families of quantum LDPC codes of the same rate.
I will discuss in this talk what can be expected from this approach when these spatially coupled LDPC codes are used for performing fault tolerant computation.
Measuring the overhead of a quantum error correcting code

Austin Fowler Institute for Quantum Computing (IQC)

July 16, 2014

PIRSA:14070014

If one's goal is large-scale quantum computation, ultimately one wishes to minimize the amount of time, number of qubits, and qubit connectivity required to outperform a classical system, all while assuming some physically reasonable gate error rate. We present two examples of such an overhead study, focusing on the surface code with and without long-range interactions.

Title	Date	Collection	Type	Info
Uni10 Tensor Network Library	2014‑08‑05	Quantum Matter	Other	View details
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.	2014‑07‑31	Quantum Gravity	Scientific Series	View details
Asymmetric Hawking Radiation : Baryogenesis from Hawking Radiation	2014‑07‑29	Particle Physics	Scientific Series	View details
Discussion with Neil Turok	2014‑07‑24	ISSYP 2014		View details
Space-Time Circuit-to-Hamiltonian construction and Its Applications	2014‑07‑23	Perimeter Institute Quantum Discussions	Scientific Series	View details
What’s Interesting These Days (With Gravity)?	2014‑07‑23	ISSYP 2014		View details
Supersymmetric AdS5 solutions in M-theory and Class S SCFT's	2014‑07‑22	Quantum Fields and Strings	Scientific Series	View details
Life as a Physicist	2014‑07‑22	ISSYP 2014		View details
Can Quantum Correlations be Explained Causally?	2014‑07‑21	ISSYP 2014		View details
Inferring causal structure: a quantum advantage	2014‑07‑17	Quantum Foundations	Scientific Series	View details
Spatially coupled quantum LDPC codes	2014‑07‑16	International Workshop on Quantum LDPC Codes	Conference	View details
Measuring the overhead of a quantum error correcting code	2014‑07‑16	International Workshop on Quantum LDPC Codes	Conference	View details

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Format results

Uni10 Tensor Network Library

Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Asymmetric Hawking Radiation : Baryogenesis from Hawking Radiation

Discussion with Neil Turok

Space-Time Circuit-to-Hamiltonian construction and Its Applications

What’s Interesting These Days (With Gravity)?

Supersymmetric AdS5 solutions in M-theory and Class S SCFT's

Life as a Physicist

Can Quantum Correlations be Explained Causally?

Inferring causal structure: a quantum advantage

Spatially coupled quantum LDPC codes

Measuring the overhead of a quantum error correcting code

Uni10 Tensor Network Library

Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Asymmetric Hawking Radiation : Baryogenesis from Hawking Radiation

Discussion with Neil Turok

Space-Time Circuit-to-Hamiltonian construction and Its Applications

What’s Interesting These Days (With Gravity)?

Supersymmetric AdS5 solutions in M-theory and Class S SCFT's

Life as a Physicist

Can Quantum Correlations be Explained Causally?

Inferring causal structure: a quantum advantage

Spatially coupled quantum LDPC codes

Measuring the overhead of a quantum error correcting code