Scientific Series

Displaying 3577 - 3588 of 5113

Fractional Chern Insulators

Titus Neupert ETH Zurich
November 29, 2012

PIRSA:12110080
Condensed Matter
Quantification and Evolution of Quantum Correlations

Asma Al-Qasimi University of Rochester
November 28, 2012

PIRSA:12110096
Quantum Information
Dyon condensation in topological Mott insulators

Gil Young Cho Pohang University of Science and Technology
November 28, 2012

PIRSA:12110087
Condensed Matter
Wiring up Quantum Systems: Fun with Artificial Atoms and Microwave Photons

Steve Girvin Yale University
November 28, 2012

PIRSA:12110041
Condensed Matter
Chern-Simons Contact Terms

Thomas Dumitrescu University of California, Los Angeles
November 28, 2012

PIRSA:12110094
Quantum Fields and Strings
Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085
Bootstrapping CFTs with the Extremal Functional Method

Miguel Paulos École Normale Supérieure - PSL
November 27, 2012

PIRSA:12110049
Quantum Fields and Strings
Bubble Baryogenesis

Gilly Elor University of California, Berkeley
November 27, 2012

PIRSA:12110091
Cosmology
Mass and Tension (momentum) Sum Rules in AdS (dS)

Jennie Traschen University of Massachusetts Amherst
November 27, 2012

PIRSA:12110042
Quantum Gravity
Dynamical Capture Compact Binary Mergers

William East Perimeter Institute for Theoretical Physics
November 22, 2012

PIRSA:12110054
Strong Gravity
Holography for inflation using conformal perturbation theory.

Paul McFadden Durham University
November 22, 2012

PIRSA:12110078
Cosmology

Fractional Chern Insulators

Titus Neupert ETH Zurich
November 29, 2012

PIRSA:12110080
Condensed Matter
Fractional Chern insulators (FCIs) are topologically ordered states of interacting fermions that share their universal properties with fractional quantum Hall states in Landau levels. FCIs have been found numerically in a variety of two-dimensional lattice models upon partially filling an almost dispersionless band with nontrivial topological character with repulsively interacting fermions. I will show how FCIs emerge in bands with Chern number C=1 and C=2 and in Z_2 topological insulators, where the latter are accompanied by a spontaneous breaking of time-reversal symmetry. Further, I will discuss the relevance of the noncommutative quantum geometry of the flat topological band to the stability of FCIs and how they can be distinguished from phases of spontaneously broken point group symmetry, such as charge density waves.
Quantification and Evolution of Quantum Correlations

Asma Al-Qasimi University of Rochester
November 28, 2012

PIRSA:12110096
Quantum Information
Dyon condensation in topological Mott insulators

Gil Young Cho Pohang University of Science and Technology
November 28, 2012

PIRSA:12110087
Condensed Matter
We consider quantum phase transitions out of topological Mott insulators in which the ground state of the fractionalized excitations (fermionic spinons) is topologically non-trivial. The spinons in topological Mott insulators are coupled to an emergent compact U(1) gauge field with a so-called "axion" term. We study the confinement transitions from the topological Mott insulator to broken symmetry phases, which may occur via the condensation of dyons. Dyons carry both "electric" and "magnetic" charges, and arise naturally in this system because the monopoles of the emergent U(1) gauge theory acquires gauge charge due to the axion term. It is shown that the dyon condensate, in general, induces simultaneous current and bond orders. When the magnetic transition is driven by dyon condensation, we identify the bond order as valence bond solid order and the current order as scalar spin chirality order. Hence, the confined phase of the topological Mott insulator is an exotic phase where the scalar spin chirality and the valence bond order coexist and appear via a single transition. If time allows, I will also discuss our recent work on the proximate symmetry-broken phases of Z2 spin liquid on Kagome lattice.
Wiring up Quantum Systems: Fun with Artificial Atoms and Microwave Photons

Steve Girvin Yale University
November 28, 2012

PIRSA:12110041
Condensed Matter
A revolution is underway in the construction of ‘artificial atoms’ out of superconducting electrical circuits. These macroscopic ‘atoms’ have quantized energy levels and can emit and absorb quanta of light (in this case microwave photons), just like ordinary atoms. Unlike ‘real’ atoms, the properties of these artificial atoms can be engineered to suit various particular applications, and they can be connected together by wires to form quantum ‘computer chips.’ This so-called ‘circuit QED’ architecture has given us the ability to do non-linear quantum optics in electrical circuits at the single photon level. It is now possible to entangle multiple qubits, count individual microwave photons, create large ‘Schrödinger cat’ photon states and perform quantum feedback. This talk will present an elementary introduction to the field.
Chern-Simons Contact Terms

Thomas Dumitrescu University of California, Los Angeles
November 28, 2012

PIRSA:12110094
Quantum Fields and Strings
Chern-Simons contact terms constitute new observables in three-dimensional quantum field theory. In N=2 supersymmetric theories with an R-symmetry, they lead to a superconformal anomaly. This understanding clarifies several puzzles surrounding the S3 partition function of these theories. In particular, it leads to a proof of the F-maximization principle. Chern-Simons contact terms can be computed exactly using localization and lead to new tests of proposed dualities.
Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
In this talk I will describe my work characterizing quantum entanglement in systems with a Fermi surface. This class includes everything from Fermi liquids to exotic spin liquids in frustrated magnets and perhaps even holographic systems. I review my original scaling argument and then describe in detail a number of new precise results on entanglement in Fermi liquids. I will also discuss recent quantum Monte Carlo calculations of Renyi entropies and will argue that we now have a rather complete agreement between theory and numerics for Fermi liquid entanglement. I will also discuss universal crossovers between thermal and entanglement entropy and a class of solvable interacting models where we can prove the universality of the Widom formula for Fermi surface entanglement. If there is time, I will comment on several other topics including fluctuations of conserved quantities and connections to holography.
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085

Most applications of the density matrix renormalization group (DMRG) have been to lattice models with short range interactions. But recent developments in DMRG technology open the door to studying continuum systems with long-range interactions in one dimension (1d). One key motivation is simulating cold atom experiments, where it is possible to engineer Hamiltonians of precisely this type. We have been applying DMRG in the 1d continuum with another motivation: to investigate and improve density functional theory (DFT). DFT has exact mathematical foundations, but in practice one must use approximations. These approximations work incredibly well for weakly correlated systems yet fail when correlations are strong. Improving DFT directly for realistic 3d systems is hard because few systems can be solved exactly. By working in the 1d continuum instead, we can use the power of DMRG to study DFT. We can implement both the exact DFT formalism and standard DFT approximations. After showing how to overcome the challenges in performing these calculations, I will discuss some of the key questions we are investigating, for example, the ability of DFT to predict gaps of insulating systems.
Bootstrapping CFTs with the Extremal Functional Method

Miguel Paulos École Normale Supérieure - PSL
November 27, 2012

PIRSA:12110049
Quantum Fields and Strings
The existence of a positive linear functional acting on the space of (differences between) conformal blocks has been shown to rule out regions in the parameter space of conformal field theories (CFTs). We argue that at the boundary of the allowed region the extremal functional contains, in principle, enough information to determine the dimensions and OPE coefficients of an infinite number of operators appearing in the correlator under analysis. Based on this idea we develop the Extremal Functional Method (EFM), a numerical procedure for deriving the spectrum and OPE coefficients of CFTs lying on the boundary (of solution space). We test the EFM by using it to rederive the low lying spectrum and OPE coefficients of the 2d Ising model based solely on the dimension of a single scalar quasi-primary -- no Virasoro algebra required. Our work serves as a benchmark for applications to more interesting, less known CFTs in the near future, such as the 3d Ising model.
Bubble Baryogenesis

Gilly Elor University of California, Berkeley
November 27, 2012

PIRSA:12110091
Cosmology
Mass and Tension (momentum) Sum Rules in AdS (dS)

Jennie Traschen University of Massachusetts Amherst
November 27, 2012

PIRSA:12110042
Quantum Gravity
The stress-energy tensor in a conformal field theory has zero trace. Hence AdS boundary stress-tensors are traceless by construction, to match this property of the dual CFT. An elegant (aka nifty) construction based on the conformal isometry of AdS will be presented which shows that in an asymptotically AdS spacetime, the sum of the ADM mass and the ADM tensions is zero. This result follows strictly from the gravitational point of view- that is, the Einstein equations and the definitions of the ADM charges. Further, it turns out that perturbative stress-energy sources in an asymptotically AdS spacetime must satisfy a local version of this constraint, namely that the sum of the energy density minus the pressures equals zero. The situation with positive cosmological constant is both similar and distinct in interesting ways, which will be briefly discussed. The analogous (analytically continued) conformal isometry in dS is the root of the ``k^4 “ power spectrum for causal cosmological perturbations. Work in progress (speculations) will be presented about a corresponding sum-rule for gravitational charges defined at future infinity in a spacetime that approaches dS at late times.
Dynamical Capture Compact Binary Mergers

William East Perimeter Institute for Theoretical Physics
November 22, 2012

PIRSA:12110054
Strong Gravity
Holography for inflation using conformal perturbation theory.

Paul McFadden Durham University
November 22, 2012

PIRSA:12110078
Cosmology
Holographic cosmology maps cosmological time evolution to the inverse RG ﬂow of a dual three-dimensional QFT. In cases where this RG ﬂow connects two closely separated ﬁxed points, QFT correlators may be calculated perturbatively in terms of the conformal ﬁeld theory associated with one of the ﬁxed points, even when the dual QFT is at strong coupling. Realising slow-roll inﬂation in these terms, we show how to derive standard slow-roll inﬂationary power spectra and non-Gaussianities through purely holographic calculations. The form of slow-roll inﬂationary correlators is seen to be determined by the perturbative breaking of conformal symmetry away from the ﬁxed point.

Title	Speaker(s)	Date	Talk Type	Info link
Fractional Chern Insulators	Titus Neupert	2012-11-29	Scientific Series	View details
Quantification and Evolution of Quantum Correlations	Asma Al-Qasimi	2012-11-28	Scientific Series	View details
Dyon condensation in topological Mott insulators	Gil Young Cho	2012-11-28	Scientific Series	View details
Wiring up Quantum Systems: Fun with Artificial Atoms and Microwave Photons	Steve Girvin	2012-11-28	Scientific Series	View details
Chern-Simons Contact Terms	Thomas Dumitrescu	2012-11-28	Scientific Series	View details
Entanglement and the Fermi surface	Brian Swingle	2012-11-27	Scientific Series	View details
Exact Calculations in the 1D Continuum for DFT and Beyond		2012-11-27	Scientific Series	View details
Bootstrapping CFTs with the Extremal Functional Method	Miguel Paulos	2012-11-27	Scientific Series	View details
Bubble Baryogenesis	Gilly Elor	2012-11-27	Scientific Series	View details
Mass and Tension (momentum) Sum Rules in AdS (dS)	Jennie Traschen	2012-11-27	Scientific Series	View details
Dynamical Capture Compact Binary Mergers	William East	2012-11-22	Scientific Series	View details
Holography for inflation using conformal perturbation theory.	Paul McFadden	2012-11-22	Scientific Series	View details

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