Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
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.
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.
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.
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.
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.
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.
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.
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.