Sommerfeld Lecture Series (ASC)

Two of the most amazing ideas in physics are the holographic

principle and quantum error correction. The holographic principle

asserts that all the information contained in a region of space is

encoded on the boundary of the region, albeit in a highly scrambled

form. Quantum error correction is the foundation of our hope that

large-scale quantum computer can be operated to solve hard

problems. I will argue that these two ideas are closely related, and

will describe quantum codes which realize the holographic

principle. These codes provide simplified models of quantum

spacetime, opening new directions in the study of quantum gravity,

though many questions remain.

Aside from enabling revolutionary future technologies, quantum

information science is providing powerful new tools for attacking

deep problems in fundamental physical science. In particular, the

recent convergence of quantum information and quantum gravity is

sparking exciting progress on some old and very hard questions.

The quantum laws governing atoms and other tiny objects seem to

defy common sense, and information encoded in quantum systems

has weird properties that baffle our feeble human minds. John

Preskill will explain why he loves quantum entanglement, the

elusive feature making quantum information fundamentally different

from information in the macroscopic world. By exploiting quantum

entanglement, quantum computers should be able to solve

otherwise intractable problems, with far-reaching applications to

cryptology, materials, and fundamental physical science. Preskill is

less weird than a quantum computer, and easier to understand.

One hundred years ago, D’Arcy Thompson – a nineteenth century

polymath, working at the turn of the twentieth century – wrote a

beautiful monograph, “On Growth and Form”, in which he pondered

the geometry of living forms and how it emerges in the process of

Morphogenesis. Thompson was ahead of his time. Genetics and

Developmental Biology have since come a long way in elucidating

the general and particular aspects of Morphogenesis, uncovering the

key genes and molecules that underlie the process in different

animals and plants. Yet, Thompson’s agenda of understanding how

developmental processes actually specify the geometry of tissues,

limbs and organs is far from complete. A particular challenge is to

bridge the gap between microscopic scales, where molecular

mechanisms operate, and the macroscopic scales of animal “shape

and form”. This challenge offers much for a Theoretical Physicist to

think about. This talk will provide some examples, relating the study

of order in the arrangement of fly wing hairs to ferromagnetism and

uncovering an unexpected wealth of mechanical phenomena in the

study of cellular flows in a fly embryo.

When we think about evolution, it is typically in the context of

natural history, seeking an explanation for the amazing diversity of life. Yet evolution is not only the matter of the past, but an ongoing dynamical process linking the past with the future. Evolutionary

dynamics is particularly apparent in rapidly mutating microbes and

viruses. For example, the virus causing seasonal flu continuously evolves to escape human immunity generated by previous

infections: because of this process, we get the flu again and again.

Can we understand evolutionary dynamics well enough to predict

the future, at least far enough to help with the flu vaccine updates?

This talk will review basic mechanisms of evolutionary dynamics and discuss some of the old and new approaches to evolutionary

forecasting and the challenges that they face. Surprisingly, ideas

from Theoretical Physics can be helpful in understanding

evolutionary dynamics.

Our understanding of simple solids, is firmly grounded on the Fermi

liquid concept and powerful computational techniques built around the

density functional theory. These ideas form the basis of our “standard

model” of solid state physics and have provided us with an accurate

description of many materials of great technological significance.

Correlated electron systems are materials for which the the standard

model of solid state physics fails dramatically. The best known example

being the copper oxide high temperature superconductors. Correlated

electron materials continue to be discovered accidentally and surprise us

with their exceptional physical properties and their potential for new

applications. The most recent example is provided by the iron arsenide

based high temperature superconductors.

From a theoretical perspective describing strongly correlated electron

systems pose one of the most difficult non-perturbative challenges in

physics. In this colloquium I will give an elementary introduction to the

field of strongly correlated electron materials and Dynamical Mean Field

Theory (DMFT) a non perturbative method which provides a zeroth order

picture of the strong correlation phenomena in close analogy with the

Weiss mean field theory in statistical mechanics. Applications materials

containing f and d electrons will be presented to show how the

anomalous properties of correlated materials emerge from their atomic

constituents.

I will conclude with an outlook of the challenges ahead and the

perspectives for a rational material design.

Strongly correlated metals exhibit anomalous transport properties

which have puzzled condensed matter physicists for many years.

They are characterized by large resistivities which exceed the Mott

Ioffe Reggel limit and large thermoelectric responses, which cannot

be explained in terms of standard Fermi liquid quasiparticles.

Dynamical Mean Field Theory (DMFT) calculations [1,2] carried out

on a doped one band Hubbard model suggest that this behavior

originate in the strong temperature dependence of thee parameters

of the underlying resilient (non-Landau) quasiparticles.

We will test these ideas by analyzing low energy optical spectroscopy

measurements in several prototypical compounds starting with

the archetypal correlated material Sesquioxide V2O3. We will also

show first principles, material specific, LDA+DMFT calculations

which are in very good agreement with the experiments [3].

Superconductivity is a state of matter where electrons can flow without

resistance and where magnetic fields are expelled. It was discovered

serendipitously more than a hundred years ago. Today, superconductors

are essential components of medical imaging devices as well as high

energy particles accelerators.

Understanding this phenomena was one of the greatest intellectual

challenges of the twentieth century. A dramatic advance was provided by

the BCS (Bardeen Cooper Schrieffer) theory 45 years after. It posits that

superconductivity is the result of macroscopic condensation of electron

pairs, which are held together by the vibrations of the lattice. The condensate

is a macroscopic quantum objects and its rigidity accounts for its

striking macroscopic properties.

The BCS theory was so successful that by the early 70’s superconductivity

was considered a completely understood subject with the maximum

achievable critical temperature having been reached experimentally

around 30K. In the late 80’s this field of research took a dramatically turn

with the discovery of new ceramic compounds which superconduct at

temperatures as high as 160 K. These materials, cannot be described by

straightforward extensions of the BCS theory. Scientists are still working

on finding new explanations for these materials and we will describe the

challenge they pose. The quest for room temperature superconductivity

thus continues. A breakthrough in this field would have unimaginable

consequences, changing the way we transmit electricity from its

generation to its consumption to the way we design computers.

Sixteenth Arnold Sommerfeld Lecture Series, The Principle of Least Action is both profound and practical. Since its first formulation by Maupertuis and Euler nearly three centuries ago, the Principle has been, and continues to be, a formidable battlehorse for penetrating unchartered territory in

theoretical physics. The Principle, its connection with, and implications for, our ideas of symmetry, space, time, quantum mechanics, thermodynamics and gravitation, are glanced at.

The Principle of Least Action is both profound and practical. Since its first formulation by Maupertuis and Euler nearly three centuries ago, the Principle has been, and continues to be, a formidable battlehorse for penetrating unchartered territory in

theoretical physics. The Principle, its connection with, and implications for, our ideas of symmetry, space, time, quantum mechanics, thermodynamics and gravitation, are glanced at.