1. The Wave Function
In quantum mechanics, the state of a particle is described by a wave function psi(x, t). The wave function is complex-valued and contains all information about the system.
2. Operators and Observables
Physical quantities are represented by Hermitian operators. The eigenvalues are the possible measurement outcomes.
| Observable | Operator | Eigenvalue Equation |
|---|---|---|
| Position | x-hat = x | x|x> = x|x> |
| Momentum | p-hat = -i*h-bar * d/dx | p|p> = p|p> |
| Energy | H = p^2/(2m) + V | H|E> = E|E> |
| Angular momentum | L = r x p | L_z|l,m> = m*h-bar|l,m> |
The Uncertainty Principle
This is not a measurement limitation but a fundamental property of nature! It arises from [x, p] = i * h-bar.
3. Spin and the Pauli Matrices
Spin is intrinsic angular momentum with no classical analog. Electrons have spin-1/2, meaning they can be in states |up> or |down>.
The Pauli Matrices
[1 0]
[i 0]
[0 -1]
These satisfy sigma_i * sigma_j = delta_ij * I + i * epsilon_ijk * sigma_k
4. Wave-Particle Duality
The double-slit experiment reveals the fundamental mystery of quantum mechanics: matter exhibits both wave and particle properties.
De Broglie Wavelength
Every particle has an associated wavelength! For an electron at 100 eV, lambda ~ 0.1 nm.
5. The Path Integral Formulation
Feynman showed that quantum mechanics can be formulated as a sum over all possible paths:
6. Connection to Z^2 Framework
Quantum mechanics provides the foundation for understanding the Z^2 framework:
Why Quantum Mechanics Matters for Z^2
- * Complex amplitudes: The fundamental description uses complex numbers
- * Spin: Fermions require spinor representations of the Lorentz group
- * Path integrals: The language of quantum field theory
- * Symmetries: Quantum numbers are eigenvalues of symmetry generators
Exercises
- For the particle in a box, show that the energy levels are E_n = n^2 * pi^2 * h-bar^2 / (2mL^2).
- Verify that the Pauli matrices satisfy [sigma_x, sigma_y] = 2i*sigma_z.
- Calculate the de Broglie wavelength of an electron with kinetic energy 100 eV.
- Show that sigma_x^2 = sigma_y^2 = sigma_z^2 = I (the identity matrix).
- For a spin-1/2 particle in state |+x>, calculate the probability of measuring spin up in the z-direction.