641 Works

3D Digital Holographic Interferometry: Applications in Biomedicine

Digital Holographic Interferometry (DHI) plays an important role in the evaluation of object static and dynamic displacements. The state of the art research on this technique is such that it is being used to solve problems in a wide variety of disciplines, from basic Physics to engineering and even social sciences. This invited plenary talk will deal with specific applications in some biomedical objects, even showing preliminary results using Electron Holography.

The impact of the Atmosphere on space-bound Vehicles

When rockets and space-bound vehicles are fired into space, they have to deal with turbulence, winds and waves in the Earth's atmosphere. Different height regimes cause different problems. In the lower regions (0 to 20 km altitude), winds and turbulence are major issues, whereas above 50 km altitude, large atmospheric waves have serious importance on safe passage. Similar issues arise on re-entry. In this talk, I will discuss the ways in which these atmospheric phenomena...

From timeless physical theory to timelessness

Peter Evans The extent to which Julian Barbour's Machian formulation of general relativity and his interpretation of canonical quantum gravity can be called timeless is addressed. We differentiate two types of timelessness in Barbour's work (1994a, 1994b and 1999) and attempt to refine Barbour's metaphysical claim by providing an account of the essential features of time through considerations of the representation of time in physical theory. We argue that Barbour's claim of timelessness is dubious...

Quantum limits for measurement of the metric tensor

Tony Downes The geometry of space-time can only be determined by making measurements on physical systems. The ultimate accuracy achievable is then determined by quantum mechanics which fundamentally governs these systems. In this talk I will describe uncertainty principles constraining how well we can estimate the components of a metric tensor describing a gravitational field. I shall outline a number of examples which can be easily constructed with a minimum of mathematical complexity. I will...

A critique of Coleman - De Luccia

In many respects, de Sitter space behaves like a system at finite temperature in finite volume. I will extend this to include the lack of first-order phase transitions. This rules out exponential decay in the de Sitter landscape, which changes the global structure in a significant way.

Matter matters in asymptotically safe quantum gravity

The Functional Renormalisation Group technique has received great attention in recent times proving itself as a powerful tool to describe the high energy behaviour of gravitational interactions.
Its key ingredient is a nontrivial fixed point of the theory renormalization group flow which controls the behavior of the coupling constants in the ultraviolet regime and ensures that physical quantities are safe from divergences. I will briefly review the main ingredients of the gravitational asymptotic safety framework...

From the symmetric group to giant gravitons in super Yang-Mills theory

In this talk we will discuss how giant gravitons and their open string interactions emerge from super Yang-Mills Theory. This is accomplished by diagonalizing the one loop dilatation operator on a class of operators with bare dimension of order N. From the result of this diagonalization, the Gauss Law governing the allowed open string excitations of giant gravitons is clearly visible. In addition, we show that this sector of the theory is integrable.

Pyrochlore Material Yb_2Ti_2O_7: A Model Quantum Spin Ice

We discuss the thermodynamic properties of the model exchange quantum spin ice material Yb_2Ti_2O_7. Using exchange parameters recently determined from high-field neutron scattering measurements, we calculate the thermodynamic properties of this model system. We find very good agreement with the heat capacity, entropy and magnetization measurements on the materials. We show that, in the weak quantum regime, quantum fluctuations lead to the selection, within the spin-ice manifold, of a conventional ordered ground state. However, the...

Numerical Holographic Striped Phases


Candidates for Principles of Quantumness

Quantum Mechanics (QM) is a beautiful simple mathematical structure--- Hilbert spaces and operator algebras---with an unprecedented predicting power in the whole physical domain. However, after more than a century from its birth, we still don't have a "principle" from which to derive the mathematical framework. The situation is similar to that of Lorentz transformations before the advent of the relativity principle. The invariance of the physical law with the reference system and the existence of...

Learning quantum models for physical and non-physical data

In this talk I address the problem of simultaneously inferring unknown quantum states and unknown quantum measurements from empirical data. This task goes beyond state tomography because we are not assuming anything about the measurement devices. I am going to talk about the time and sample complexity of the inference of states and measurements, and I am going to talk about the robustness of the minimal Hilbert space dimension. Moreover, I will describe a simple...

Cluster Polylogarithms for Scattering Amplitudes

Motivated by the cluster structure of two-loop scattering amplitudes in N = 4 Yang-Mills theory we define cluster polylogarithm functions. We find that all such functions of weight 4 are made up of a single simple building block associated to the A2 cluster algebra. Adding the requirement of locality on generalized Stasheff polytopes, we find that these A2 building blocks arrange themselves to form a unique function associated to the A3 cluster algebra. ThisA3 function...

Towards a 1/c Expansion in 2d Conformal Field Theory

I will describe progress in deriving 3d gravity directly from 2d conformal field theory at large central charge 'c'. In a large class of CFTs, using general arguments like modular invariance, crossing symmetry, and the OPE expansion, the spectrum, the entanglement entropy, and certain partition functions can be computed to leading order in a 1/c expansion. The results agree with universal features of 3d gravity required by black hole thermodynamics and the Ryu-Takayanagi formula; furthermore,...

Superconducting quantum criticality of Dirac fermions

The semimetal-superconductor quantum phase transition of 2D Dirac fermions, such as found on the surface of a topological insulator, is conjectured to exhibit an emergent N=2 supersymmetry, based on a one-loop renormalization group analysis. In this talk I will present further evidence for this conjecture based on a three-loop analysis. Assuming the conjecture is true, I will present exact results for certain critical properties including the optical conductivity, shear viscosity, and entanglement entropy at zero...

Nuclear Theory/Heavy Ions 3

Particle Physics 6

Introduction to additivity problems and Hastings' counterexample


Descent Equations, Gauge Structure in Configuration Space and Topology of Quantum Field Theory - Yongshi Wu

Topological aspects of physical systems, including the called topological states of matter, have become hot topics in the frontiers of physics in recent years. Here I would like to present a mathematically "popular" talk for professional physicists for a highlight or overview of how one can systematize knowledge of topological aspects of quantum field theories. Our starting points are Descent Equations and Gauge Structure in Configuration Space in Field Theory. (The audience needs only to know the meaning of "differential...

Discussion 2

PI Day - Mar. 14th, 2018 - Part 1

Universal quantum computation in thermal equilibrium

Adiabatic quantum computation (AQC) is a method for performing universal quantum computation in the ground state of a slowly evolving local Hamiltonian, and in an ideal setting AQC is known to capture all of the computational power of the  quantum circuit model.  However, despite having an inherent robustness to noise as a result of the adiabatic theorem and the spectral gap of the Hamiltonian, it has...

The Hidden Phase Space of our Universe

By combining insights from black holes and string theory we argue for the existence of a hidden phase space associated with an underlying fast dynamical system, which is largely invisible from a macroscopic point of view. The dynamical system is influenced by slow macroscopic observables, such as positions of objects. This leads to a collection of reaction forces, whose leading order Born Oppenheimer force is determined by the general principle that the phase space volume...

What to do if quantum channels are not noiseless enough

This talk is concerned with the noise-insensitive transmission of quantum information. For this purpose, the sender incorporates redundancy by mapping a given initial quantum state to a messenger state on a larger-dimensional Hilbert space. This encoding scheme allows the receiver to recover part of the initial information if the messenger system is corrupted by interaction with its environment. Our noise model for the transmission leaves a part of the quantum information unchanged, that is, we...

Challenges of Explaining Cosmic Acceleration Through Modified Gravity

Among the possible explanations for the observed acceleration of the universe, perhaps the boldest is the idea that new gravitational physics might be the culprit. In this colloquium I will discuss some of the challenges of constructing a sensible phenomenological extension of General Relativity, give examples of some candidate models of modified gravity and survey existing observational constraints on this approach. I will conclude by discussing how we might hope to distinguish between modifications of...

Visualizing Quantum Matter

Recently developed techniques allow imaging of electronic quantum matter directly at the atomic scale. I will introduce the basic principles and describe the set of observables available from these techniques. As examples, I will survey visualization of exotic forms of electronic quantum matter including heavy fermions, quantum critical electrons, topological surface states, electronic liquid crystals, and high temperature superconductors.

Registration Year

  • 2022

Resource Types

  • Audiovisual


  • Perimeter Institute