Quantum threshold theorem Updated 2025-07-16
This theorem roughly states that states that for every quantum algorithm, once we reach a certain level of physical error rate small enough (where small enough is algorithm dependant), then we can perfectly error correct.
This algorithm provides the conceptual division between noisy intermediate-scale quantum era and post-NISQ.
Quantum electrodynamics Lagrangian Updated 2025-07-16
where:
Note that this is the sum of the:
Note that the relationship between and is not explicit. However, if we knew what type of particle we were talking about, e.g. electron, then the knowledge of psi would also give the charge distribution and therefore
Video 1.
Particle Physics is Founded on This Principle! by Physics with Elliot (2022)
Source.
TODO find/create decent answer.
I think the best answer is something along:
A basic non-precise intuition is that a good model of reality is that electrons do not "interact with one another directly via the electromagnetic field".
A better model happens to be the quantum field theory view that the electromagnetic field interacts with the photon field but not directly with itself, and then the photon field interacts with parts of the electromagnetic field further away.
The more precise statement is that the photon field is a gauge field of the electromagnetic force under local U(1) symmetry, which is described by a Lie group. TODO understand.
This idea was first applied in general relativity, where Einstein understood that the "force of gravity" can be understood just in terms of symmetry and curvature of space. This was later applied o quantum electrodynamics and the entire Standard Model.
Bibliography:
Photon field Updated 2025-07-16
Feynman diagram Updated 2025-07-16
I think they are a tool to calculate the probability of different types of particle decays and particle collision outcomes. TODO Minimal example of that.
And they can be derived from a more complete quantum electrodynamics formulation via perturbation theory.
At Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979), an intuitive explanation of them in termes of sum of products of propagators is given.
Quantum control systems use FPGAs Updated 2025-07-16
It seems that all/almost all of them do. Quite cool.
Video 1.
FPGA Architecture of the Quantum Control System by Keysight (2022)
Source. They actually have a dedicated quantum team! Cool.
Video 2.
FPGA based servo system by Atoms & Laser (2018)
Source. The Indian lady is hardcore.

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