# Physics

## Understanding Physical Systems

These are short presentations I've given over the years on topics that I found interesting. They are informal, educational, and accessible to a physics audience . They emphasize basic understanding and simple mental models, mostly mimicing how I learned to think about these systems.

Not guaranteed to be accurate, or at an advanced level. Just my understandings and interpretations at the time.

### Controlling small quantum objects

Excitons - Understanding excitons in 2D semiconductors (2021) (slides)

Superconducting qubits - Comparing superconducting qubits to neutral atoms (2020) (slides)

Quantum dots - Why can we trap single electrons in quantum dots? (2017) (slides)

Quantum scattering - Feshbach resonances and scattering in neutral atoms (2020) (slides)

### Phenomena in physics

## Simplifying Theoretical Formalisms

Physics is full of baggage and complicated terminology, some topics more than others. These are my attempts to cut through the noise.

The problem: subfields like statistical mechanics have many seemingly disconnected parts. It's hard to remember how they all fit together.

The solution: replace everything with one simple idea or one mental model. Learn this idea well, and know how to use it to derive everything else.

### Interactions in quantum mechanics

File: Term paper in atomic physics on the resolvent formalism.

This paper provides a simple approach to understanding interacting quantum mechanical systems. The goal was to go directly from the Schrödinger equation to many complicated phenomena in quantum mechanics in as few steps as possible.

### Statistical mechanics

Files: my PhD thesis (pages 57-60) and an explanation I wrote on entropy and statistical mechanics for a high school physics competition (a bit more verbose and less focused).

These documents provide a single unifying framework for understanding most of statistical mechanics, regardless of the physical system, and constraints. The goal is to be able to look at any physical system, and immediately recognize what variables fit in different general categories. Then all you have to remember is how the general categories work.

You don't have to remember the difference between enthalpy and entropy and the Gibbs or Hemholtz or some other type of free energy.

All you have to ask about a variable is a few general questions, like: is it conserved? shared with a bath? controlled by the user?

As a side benefit this gives a clear picture of what work is, and why it is related to free energy.