Class Information Review Aside: Single Photon Generation Harmonic Oscillator Principles of Quantum Mechanics Commutators Identical Particles Two Particle Systems Bosons and Fermions Exchange Forces Solids Free Electron Gas Band Structure Bloch’s Theorem Dirac Comb Conservation Laws Translations Translated Operators Translational Symmetry Discrete Translational Symmetry Continuous Translational Symmetries Parity Parity Selection Rules Rotational Symmetry Object Classifications Degeneracy Wigner-Eckart Theorem Time Translation Heisenberg Picture Time-Independent Peturbation Theory Degenerate Peturbation Theory Fine Structure of Hydrogen Spin-Orbit Coupling (fine structure) Variational Principle Quantum Dynamics Two Level System Electromagnetic Radiation Peturbations Einstein Coefficients Fermi’s Golden Rule Class Information Grade Breakdown: HW 20%, Midterm 35%, Final 45% Midterm October 19th Book: Griffith’s Quantum Mechanics 3rd Edition Review Matter and light can both act as either particles or waves Double Slit experiment Can describe non-relativistic particles by Schrodinger’s Equation $i\hbar \frac{\partial}{\partial t}\Psi = -\frac{\hbar^2}{2m}\nabla^2 \Psi +V(r) \Psi(r,t)$ Can transform to positional representation via Fourier Transform Physical interpretation: $|\Psi(x,t)|^2$ tells you the probability that the particle is located at a certain position at a certain time (or has a certain momentum at a certain time) You can calculate the expectation value of an observable Q: $ <Q> = \int \Psi^{*} \hat{Q} \Psi dx $ Specific operators include: $\hat{x} = x$ $\hat{p} = -i\hbar \frac{\partial}{\partial x}$ Derived as follows: $ <p> = m \frac{\partial}{\partial t} <x> = m\frac{ \partial}{\partial t} \int x |\Phi|^2 dx$ Use Schrodinger Equation to convert time partial to space partial, then integrate by parts to get: $ <p> = -i\hbar \int \Psi^{*}\frac{\partial}{\partial x} \Psi dx$ All other operators can be written as a function of x and p Fundamental commutation rule: $[x,p] = xp-px = i\hbar$ Aside: Single Photon Generation Pass a photon through a nonlinear medium where the polarization goes as a power of the electric field This nonlinearity causes parametric down conversion, which is the process where a photon of higher energy gets converted to two photons of lower energies $\hbar\omega_{1} = \hbar\omega_{2}+\hbar\omega_{3}$ Most of the photons pass through the crystal, but a few undergo this process Hence, if you detect a photon of $\hbar\omega_{3}$, you will be gaurenteed to detect a photon of energy $\hbar\omega_{2}$ You know that an event has happened, but you don’t know exactly when an event will occur (probabilistic) Extremely difficult to scale up Harmonic Oscillator $\hat{a} = \frac{1}{\sqrt{2m\hbar \omega}}(m\omega \hat{x}+i\hat{p})$ $\hat{a^{+}} = \frac{1}{\sqrt{2m\hbar \omega}}(m\omega \hat{x}-i\hat{p})$ $[\hat{a},\hat{a^{+}}] = 1$ $\hat{H} = \hbar \omega (\hat{a^{+}}\hat{a}+\frac{1}{2})$ $[\hat{a^{+}},\hat{H}] = -\hbar\omega \hat{a^{+}}$ $[\hat{a},\hat{H}] = \hbar\omega \hat{a}$ Successively applying $\hat{a^{+}}$ and $\hat{a}$ to to eigenfunctions of $\hat{H}$ also yields eigenfunctions with energies raised/lowered by $\hbar \omega$....