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# Vidéotheque

Since 2002 Perimeter Institute has been recording seminars, conference talks, public outreach events such as talks from top scientists 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 and 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.

Accessibly by anyone with internet, Perimeter aims to share the power and wonder of science with this free library.

## Summer Undergrad 2020 - Quantum Information - Lecture 3

Vendredi mai 29, 2020
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## Conformal blocks in genus zero, and Elliptic cohomology

Jeudi mai 28, 2020
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A fundamental theorem in the theory of Vertex algebras (known as Zhu’s theorem) demonstrates that the space generated by the characters of certain Vertex algebras is a representation of the modular group. We will cast this theorem in the language of homotopy theory using the language of conformal blocks. The goal of this talk is to justify the claim that equivariant elliptic cohomology, seen as a derived spectrum, is a homotopical analog of Zhu’s theorem in the special case of the Affine Vacuum vertex algebra at a fixed integral level.

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## Summer Undergrad 2020 - Numerical Methods (A) - Lecture 2

Jeudi mai 28, 2020
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Tensor product spaces & many-body quantum states and operators; Limiting cases  of two-site Ising model

## Conformal Geometry of Null Infinity, including gravitational waves

Jeudi mai 28, 2020
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Since the seminal work of Penrose, it has been understood that conformal compactifications (or "asymptotic simplicity") is the geometrical framework underlying Bondi-Sachs' description of asymptotically flat space-times as an asymptotic expansion. From this point of view the asymptotic boundary, a.k.a "null-infinity", naturally is a conformal null (i.e degenerate) manifold. In particular, "Weyl rescaling" of null-infinity should be understood as gauge transformations.

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## Nonlinear dynamical tides in white dwarf binaries

Jeudi mai 28, 2020
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Compact white dwarf (WD) binaries are important sources for space-based gravitational-wave (GW) observatories, and an increasing number of them are being identified by surveys like ELM and ZTF. We study the effects of nonlinear dynamical tides in such binaries. We focus on the global three-mode parametric instability and show that it has a much lower threshold energy than the local wave-breaking condition studied previously. By integrating networks of coupled modes, we calculate the tidal dissipation rate as a function of orbital period.

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## Quasi-elliptic cohomology theory and the twisted, twisted Real theories

Jeudi mai 28, 2020
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Quasi-elliptic cohomology is closely related to Tate K-theory. It is constructed as an object both reflecting the geometric nature of elliptic curves and more practicable to study than most elliptic cohomology theories. It can be interpreted by orbifold loop spaces and expressed in terms of equivariant K-theories. We formulate the complete power operation of this theory. Applying that we prove the finite subgroups of Tate curve can be classified by the Tate K-theory of symmetric groups modulo a certain transfer ideal.

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## Sigma-VOA correspondence

Jeudi mai 28, 2020
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In this talk I will discuss an interesting phenomenon, namely a correspondence between sigma models and vertex operator algebras, with the two related by their symmetry properties and by a reflection
procedure, mapping the right-movers of the sigma model at a special
point in the moduli space to left-movers. We will discuss the examples
of N=(4,4) sigma models on $T^4$ and on $K3$. The talk will be based
on joint work with Vassilis Anagiannis, John Duncan and Roberto
Volpato.

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## Summer Undergrad 2020 - Path Integrals (M) - Lecture 2

Jeudi mai 28, 2020
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## Elliptic characteristic classes, bow varieties, 3d mirror duality

Mercredi mai 27, 2020
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We study elliptic characteristic classes of natural subvarieties in some ambient spaces, namely in homogeneous spaces and in Nakajima quiver varieties. The elliptic versions of such characteristic classes display an unexpected symmetry: after switching the equivariant and the Kahler parameters, the classes of varieties in one ambient space coincide” with the classes of varieties in another ambient space. This duality gets explained as “3d mirror duality” if we regard our ambient spaces as special cases of Cherkis bow varieties. I will report on a work in progress with Y.

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## Quantum homeopathy works: Efficient unitary designs with a system-size independent number of non-Clifford gates

Mercredi mai 27, 2020
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Many quantum information protocols require the implementation of random unitaries. Because it takes exponential resources to produce Haar-random unitaries drawn from the full n-qubit group, one often resorts to t-designs. Unitary t-designs mimic the Haar-measure up to t-th moments. It is known that Clifford operations can implement at most 3-designs. In this work, we quantify the non-Clifford resources required to break this barrier.

## Lectures On-Demand

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