Quantum Mechanics

Oberlin College Physics 312

Syllabus for Fall 2023

Learning goals: Through your work in this course, you will

Aldo Leopold wrote "We speak glibly of . . . education, but what do we mean by it? If we mean indoctrination, then let us be reminded that it is just as easy to indoctrinate with fallacies as with facts. If we mean to teach the capacity for independent judgment, then I am appalled by the magnitude of the task." The ultimate goal of this course (and, I hope, of all your other courses) is to develop your capacity for thoughtful, informed, independent judgment.

Teacher: Dan Styer, Wright 215, 440-775-8183, Dan.Styer@oberlin.edu
home telephone 440-281-1348 (9:00 am to 8:00 pm only).
Instructions for meeting with me are given under "Schedule" here.

Pronouns, nouns, adjectives, and the character of science: I don't care what pronouns you use when referring to me. Similarly, you may call me "Dan", or "Mr. Styer", or "Dr. Styer", or "Prof. Styer", whichever you find most comfortable. My personal preference, however, is that you call me "Dan". In this course I will present upsetting conclusions violently opposed to our common sense and common experience. (For example: That if a particle has a position, then it doesn't have a velocity. And if it has an energy, then it doesn't have either a position or a velocity. I make no apologies for presenting upsetting conclusions: An education that avoids difficult or disturbing issues is no education at all.) I hope you'll accept those conclusions because they are based on experimental evidence and on cogent, clear, fact-based reasoning -- experiments and reasoning that you or I or anyone else could execute. If you accept those conclusions instead because I have earned the right to put a fancy shingle in front of my name, my teaching will have been an abject failure.

Meeting times: Class: MWF at 11:00 am. Conference: Monday at 3:30 pm. Wright Laboratory room 114.

Course web site: http://www.oberlin.edu/physics/dstyer/QM.
I will post handouts, problem assignments, and model solutions here.

Textbooks: (All are optional.)

Color code: Sometimes I will need to represent many different types of entities on the chalkboard simultaneously. To help keep these different sorts of things straight, I will use various colors. (Some students have found it helpful to take notes with a variety of colored pens.) I will use

the color:    to represent:
olive green    potential energy functions
blue    energy eigenvalues
red    energy eigenfunctions

Problem assignments: Posted on the course web site every Wednesday (unless there is an exam), due at the start of class the following Wednesday. My model solutions will be posted at the end of this class, so late assignments cannot usually be accepted (I may make an exception in the case of a health or family emergency). In writing your solutions, do not just write down the final answer. Show your reasoning and your intermediate steps. Describe (in words) the thought that went into your work as well as describing (in equations) the mathematical manipulations involved. For numerical results, give units and apply significant figures.

Why do you have to "show your reasoning and your intermediate steps"? Suppose someone claimed "I won reelection in November 2020. I won by a landslide." but could not provide evidence supporting his assertion. Would you belive him? I hope not. Similarly with any scientific (or non-scientific) problem. If you merely present the answer without showing supporting data or reasoning, you have not solved the problem.

The very name "reasoned discourse" means that you present not only your conclusion, but also the reasoning behind that conclusion. If you present only your result, you are not engaged in reasoned discourse.

You are welcome to consult the library, the Internet, AI resources such as ChatGPT, your friends, or your enemies in working the assigned problems, but the final write-up must be entirely your own: you may not copy word for word or equation for equation. When you do obtain outside help you must acknowledge it. (E.g. "By integrating Griffiths equation [8.5] I find that. . ." or "Employing the substitution u = sin(x) (suggested by Carol Hall). . ." or even "In working these problems I benefited from discussions with Mike Fisher and Jim Newton.") Such an acknowledgement will never lower your grade; it is required as a simple matter of intellectual fairness. Each assignment will be graded by a student grader working under my close supervision.

Exams: There will be two in-semester exams and a final. All will be two-hour open-book open-library open-Internet written exams. The in-semester exams will be due at 11:00 am on Wednesday 4 October and on Wednesday 15 November; the final exam will be due at 4:00 pm on Monday 18 December (the time set by the registrar). No collaboration is permitted in working the exams. Calculators are permitted. Before each exam I will distribute a sample exam.

Grading: Each exam contributes 20% to your final grade, and your work on the problem assignments contribute 40%. Anyone earning a final score of 50% or lower will not receive credit for this course.

Topics: (tentative)

  1. The phenomena of quantum mechanics.
    Why do we need a quantum mechanics? The Stern-Gerlach experiment and two-state systems. Quantization, interference, entanglement.
  2. Forging mathematical tools for quantum mechanics.
    What is a quantal state? State vectors, outer products, operators, and measurements -- all for two-state systems. Linear algebra. Formalism ("postulates").
  3. Time evolution.
    The time development operator and the Schrödinger equation. Application to a two-state system: the ammonia maser. Formal properties of time evolution.
  4. The quantum mechanics of position.
    One particle in one dimension -- wavefunction. Two nonidentical particles in one dimension -- configuration space. The Hamiltonian and momentum operators in one dimension. The classical limit (Ehrenfest's theorem).
  5. The infinite square well.
    Energy eigenstates. Time development.
  6. Motion of a free particle.
  7. The simple harmonic oscillator.
    Energy eigenstates through differential equations and through operator factorization. Time development.
  8. Perturbation theory.
    Approximate solutions for the energy eigenproblem.
  9. More dimensions, more particles.
  10. Angular momentum.
    Rotations and symmetries. Eigenproblem. Projections.
  11. Central force motion.
    Use of angular momentum. The Coulomb problem. Hydrogen atom fine structure.
  12. Identical particles.
  13. Return to conceptual foundations.
    Quantal motion as a sum over classical paths.

Quantum Mechanics Bibliography

Here are some books on reserve in the Science Center Library. (They are located on shelves along the south wall, not far to your right when you enter, near some comfy chairs to encourage browsing.)

Popular works:

D.F. Styer, The Strange World of Quantum Mechanics [Science QC174.12.S879 2000].
The calculational machinery of quantum mechanics is so magnificent and so formidable that it is easy to lose sight of what you're trying to calculate. This book works to keep the mathematics from obscuring the physics. (Tips for getting the most out of this book are at http://www.oberlin.edu/physics/dstyer/StrangeQM/.)

R.P. Feynman, QED: The Strange Theory of Light and Matter [Science QC793.5.P422F48 1985].
Another book, beautifully written, that emphasizes physics over mathematical technique. (Tips for getting the most out of this book are at http://www.oberlin.edu/physics/dstyer/TeachQM/QED.html.)

Books with a conceptual orientation:

R.P. Feynman and A.R. Hibbs, Quantum Mechanics and Path Integrals, chapter 1 [Science QC174.12 .F484 2010].
Tips for getting the most out of this book are at http://www.oberlin.edu/physics/dstyer/FeynmanHibbs/.

G. Greenstein and A. Zajonc, The Quantum Challenge: Modern Research on the Foundations of Quantum Mechanics [Science QC174.12.G73 2006].
Books on the foundations of quantum mechanics often wallow in vague philosophy. This one is full of crisp experiments.

S. Brandt and H.D. Dahmen, The Picture Book of Quantum Mechanics [Science QC174.12.B73 1995].
Generally good for developing that elusive quantal intuition, and particularly good concerning identical particles.