# Lecture courses

Lecture notes (mostly hand-written) for various courses I've taught (or, sometimes, attended).

Note that though I have checked the notes for typos and mistakes, this by no means guarantees there are none! If you think you've spotted one, let me know.

Unless otherwise stated, all lecture notes linked from this web site are copyright ©Toby Cubitt, and are licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

# Quantum Computation and Algorithms course

Quantum Computation and Algorithms course

Quantum computing is the flagship quantum technology. Peter Shor's 1994 quantum factoring algorithm kicked off a wave of interest and excitment about quantum computing, and is in large part responsible for the field of quantum information going mainstream. A second wave of even more excitment has been kicked off recently by the near-term prospect of NISQ hardware (noisy, intermediate-scale quantum computers) – i.e. quantum computing hardware that is not obviously useful for anything… but no longer obviously useless either!

However, there is also currently a lot of hype and many unrealistic expectations. The aim of this course is to show you where all the excitment derives from, rigorously and in detail; and to innoculate you against the over-hype.

# Complexity and Computability in Physics course

Complexity and Computability in Physics course Lecture course on quantum complexity theory, encompassing (a brief intro to) computability and complexity theory, complexity theory in quantum physics, and computability theory in physics. Lectured at the 2018 Boulder quantum information summer school.

## Lecture videos and notes

- Lecture 1, Computation and Complexity video and lecture notes
- Lecture 2: Complexity in Physics video and lecture notes
- Lecture 3: Computability in Physics video and lecture notes

# Advanced Quantum Information Theory course

Advanced Quantum Information Theory course

Quantum information theory is neither wholly physics (though it's mostly about quantum mechanics), nor wholly mathematics (though it mostly proves rigorous mathematical results), nor wholly computer science (though it's mostly about storing, processing, or transmitting information). Over the last two decades, it has developed into a rich mathematical theory of information in quantum mechanical systems, that draws on all three of these disciplines. More recently, this has been turned on its head: quantum information is beginning to be *used* to attack deep problems in physics, computer science, and mathematics.

The aim of this course is to select one or two advanced topics in quantum information theory, close to the cutting edge of research, and cover them in some depth and rigour.

This time around, I will focus on quantum information in many-body systems. What do these two topics have to do with each other? Quantum computation aims to engineer complex many-body systems to process information in ways that would not be possible classically. Many-body physics aims to understand the complex behaviour of naturally-occurring many-body systems. In a sense, they are two sides of the same coin. Quantum information theory is now used both to prove important results in many-body physics, and to construct many-body models that exhibit very unusual physics, providing counterexamples to long-standing beliefs in condensed matter theory. This is now one of the fastest-developing areas of the field.

# Quantum Computation and Complexity course

Quantum Computation and Complexity course Lectured at the 2016 Autrans summer school on Stochastic Methods in Quantum Mechanics. The notes are adapted from the first half my Advanced Quantum Information Theory course.

## Lecture notes

- Lectures 1-2: Computation and Complexity
- Lecture 3: Local Hamiltonians
- Lectures 3-4: Kitaev's Theorem
- Lecture 4: Local clock construction

# Matrix Product States and PEPS

Matrix Product States and PEPS Notes from David Perez-Garcia's lecture course on Matrix Product States and PEPS at the 2016 Autrans summer school on Stochastic Methods in Quantum Mechanics.

The slides are courtesy of David. The lecture notes are my handwritten notes from the whiteboard section of David's lectures. All content by David; all mistakes by me!

## Lecture notes

- MPS motivation (slides)
- MPS lecture notes (handwritten)
- PEPS and topological order (slides)

(The slides are copyright © 2016 David Perez-Garcia, with all rights reserved. The handwritten notes are copyright © 2016 Toby Cubitt, and are licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.)

# Decoupling Method in Quantum Shannon Theory

Decoupling Method in Quantum Shannon Theory Originally lectured in 2015 as part of the quantum information theory masters course for the UCL quantum CDT.

## Lecture Notes

## Recommended reading

Much of the material covered here (and more!) was originally proven in the Mother of All Protocols paper by Abeyesinghe, Devetak, Hayden and Winter.

These notes largely follow Section 10.9 of Preskill's wonderful lecture notes, with a (very) few modifications and additions.

# Quantum Mechanics for Mathematicians course

Quantum Mechanics for Mathematicians course Lectured in 2011 as the first section of a "Mathematics for Quantum Information" masters course given in the mathematics faculty of the Universidad Complutense de Madrid.

## Lecture Notes

- Section 0: Dirac notation;

Section 1: The postulates of quantum mechanics

(lecture 1) - Section 2: Combining quantum systems: tensor products

(lecture 2) - Section 3: Non-locality and Bell inequalities

(lecture 3) - Section 4: Ensembles and density operators;

Section 5: Taking quantum systems apart: reduced states and the partial trace;

Section 6: A brief introduction to entropy

(lecture 4)

# Quantum Mechanics course

Quantum Mechanics course Lectured from 2007 to 2010 as the second part of the 3rd year mathematics undergraduate "Quantum Mechanics" course at the University of Bristol.

## Lecture Notes

- Section 1: Angular Momentum and Spin

(lectures 1 and 2) - Section 2: Representations of Angular Momentum

(lectures 3 to 5) - Section 3: Orbital Anglular Momentum

(bonus lecture) - Section 4: Measurement

(lecture 6) - Section 5: Multiple Particles and Tensor Products

(lectures 7 and 8) - Section 6: Non-Locality and Bell Inequalities

(lectures 9 and 10)

# Classical mechanics and electrodynamics

Classical mechanics and electrodynamics I have left up some of the material I prepared for classical mechanics and electrodynamics courses taught by Prof. Weise at the TUM (many, many years ago!) in case it's of use to someone.

## Question Sheet Solutions

Given that the question sheets are substantially re-used in subsequent semesters, I've removed the worked solutions that were available here, to help you avoid the temptation to…ahem…short-cut the valuable learning process that struggling to solve the questions provides. (Believe it or not, the question sheets are not some obscure form of torture dreamed up by bitter and twisted physics professors).

If anyone involved in teaching the courses is interested in obtaining the solutions, drop me an email. I have scanned copies for about half the mechanics question sheets and all the electrodynamics question sheets.