Talks

9157 - 9168 of 16765 Results

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

Quantum Fields and Strings
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 Foundations
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
Homological product codes

Sergey Bravyi IBM (United States)

July 16, 2014

PIRSA:14070013
Gauge color codes

Hector Bombin PsiQuantum Corp.

July 16, 2014

PIRSA:14070012
Is scalable quantum error correction realistic? Some projects, thoughts and open questions.

Barbara Terhal Delft University of Technology

July 15, 2014

PIRSA:14070010
Exploring N=1 theories of class S through Higgsing, dualizing and twisting

Jaewon Song University of California, San Diego

July 15, 2014

PIRSA:14070024

Quantum Fields and Strings
TBA

John Preskill California Institute of Technology (Caltech) - Division of Physics Mathematics & Astronomy

July 15, 2014

PIRSA:14070009

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

Quantum Fields and Strings

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 Foundations

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.
Homological product codes

Sergey Bravyi IBM (United States)

July 16, 2014

PIRSA:14070013

All examples of quantum LDPC codes known to this date suffer from a poor distance scaling limited by the square-root of the code length. This is in a sharp contrast with the classical case where good LDPC codes are known that combine constant encoding rate and linear distance. In this talk I will describe the first family of good quantum "almost LDPC" codes. The new codes have a constant encoding rate, linear distance, and stabilizers acting on at most square root of n qubits, where n is the code length. For comparison, all previously known families of good quantum codes have stabilizers of linear weight. The proof combines two techniques: randomized constructions of good quantum codes and the homological product operation from algebraic topology. We conjecture that similar methods can produce good quantum codes with stabilizer weight n^a for any a>0. Finally, we apply the homological product to construct new small codes with low-weight stabilizers.

This is a joint work with Matthew Hastings
Preprint: arXiv:1311.0885
Gauge color codes

Hector Bombin PsiQuantum Corp.

July 16, 2014

PIRSA:14070012

I will describe a new class of topological quantum error correcting codes with surprising features. The constructions is based on color codes: it preserves their unusual transversality properties but removes important drawbacks. In 3D, the new codes allow the effectively transversal implementation of a universal set of gates by gauge fixing, while error-dectecting measurements involve only 4 or 6 qubits. Furthermore, they do not require multiple rounds of error detection to achieve fault-tolerance.
Is scalable quantum error correction realistic? Some projects, thoughts and open questions.

Barbara Terhal Delft University of Technology

July 15, 2014

PIRSA:14070010
Exploring N=1 theories of class S through Higgsing, dualizing and twisting

Jaewon Song University of California, San Diego

July 15, 2014

PIRSA:14070024

Quantum Fields and Strings

We study a class of 4d N=1 SCFTs obtained from partial compactifications of 6d N=(2, 0) theory on a Riemann surface with punctures. We identify theories corresponding to curves with general type of punctures through nilpotent Higgsing and Seiberg dualities. The `quiver tails' of N=1 class S theories turn out to differ significantly from N=2 counterpart and have interesting properties. Various dual descriptions for such a theory can be found by using colored pair-of-pants decompositions. Especially, we find N=1 analog of Argyres-Seiberg duality for the SQCD with various gauge groups. We compute anomaly coefficients and superconformal indices to verify our proposal.
TBA

John Preskill California Institute of Technology (Caltech) - Division of Physics Mathematics & Astronomy

July 15, 2014

PIRSA:14070009

Title	Date	Collection	Type	Info
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
Homological product codes	2014‑07‑16	International Workshop on Quantum LDPC Codes	Conference	View details
Gauge color codes	2014‑07‑16	International Workshop on Quantum LDPC Codes	Conference	View details
Is scalable quantum error correction realistic? Some projects, thoughts and open questions.	2014‑07‑15	International Workshop on Quantum LDPC Codes	Conference	View details
Exploring N=1 theories of class S through Higgsing, dualizing and twisting	2014‑07‑15	Quantum Fields and Strings	Scientific Series	View details
TBA	2014‑07‑15	International Workshop on Quantum LDPC Codes	Conference	View details

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