Introduction to Second Quantization . Instead of tracking individual particles, you treat the number of particles as an operator, which is essential for condensed matter and nuclear physics.
The "weirdness" of QM becomes more structural. You stop asking "why is it like this?" and start asking "how does this symmetry manifest in the Lagrangian?" Recommended Resources Advanced Quantum Mechanics
AQM is the "filter" course. It’s demanding and often abstract, but it is the only way to understand how the universe works at high energies. If you can master the and S-Matrix theory , you are ready for the world of Particle Physics. Introduction to Second Quantization
into the territory where spin-1/2 particles and anti-matter emerge naturally from the math. You stop asking "why is it like this
The gold standard for clarity and modern notation.
Still the best for building physical intuition before the math gets too heavy. Final Verdict