# AJL - condensed matter

## Reflections on the past, present and future of condensed matter physics

http://people.physics.illinois.edu/Leggett/APS2016-LargerWithMorePages.pdf

- (mini?) Paradigm shifts in CMP

Landa-Fermi liquid - 1956

BCS - 1957

RG and 2nd order transitions - 1963-71

FQHE

quantum information - it from bit

- mentioned briefly

one thinks of superfluid 3-He (1972), the integral quantum Hall effect (1980), cuprate superconductivity (1986), and most recently topological insulators (2004)

- not mentioned

Anderson localization

Kosterlitz-Thouless

## further insights

Philippe Nozieres has a quote with which I heartily agree: ‘‘only simple qualitative arguments can reveal the underlying physics

....but the ones where we literally do not know what questions to ask!

You may not in the end solve them, but in the long run they are the

ones really worth doing.

gave it an enormous fillip and at the same time introduced the

novel idea of quasiparticles, which bear no simple relationeither to the underlying particles (as do Landau quasiparticles in a Fermi liquid) or to the underlying classical waves (as do the phonons in a typical insulator).

- The impact of quantum information: as mentioned above,
**I believe this will in the long run be profound**

The present author would query whether the majority of the community has yet fully

caught up with the implications of this mini-revolution

- condensed matter physics to test the quantum mechanics of a macroscopic variable-(perhaps an
**‘‘invisible” paradigm shift**..

And as to the latter, it is topology, in

the sense of the need for the wave function to be single-valued,

which is at the root of just about every quantum phenomenon in

many-body physics

## Quantum Computation and Quantum Information Michael A. Nielsen & Isaac L. Chuang

Condensed Matter Theory from a Quantum Information Perspective (Lecture 10) - Anthony Leggett - 2015

## the problems

- a classification into known unknowns (low-energy excitations in glasses?) and unknown unknowns (measurement paradox?, ) ????

https://medium.com/@andreamantovani/known-knowns-known-unknowns-unknown-unknowns-leadership-367f346b0953

https://en.wikipedia.org/wiki/There_are_known_knowns