Rich Noer: Quantum Entanglement
Expanded description: Albert Einstein was deeply ambivalent about the theory of Quantum Mechanics (developed by others in the late 1920s, building on his 1905 proposal of light quanta, or photons). Seen by most physicists as immensely successful, QM did however seem to imply certain strange behaviors: events that could only be predicted statistically, and particle properties that did not exist until actually measured. Einstein argued in a now famous 1935 paper that the QM-predicted outcome of a certain hypothetical experiment would exhibit “spooky action at a distance”: two particles, once “entangled” by their common origin and shot off in opposite directions, would forever remain entangled, such that whatever happens to the “left” particle would be found to instantaneously influence the “right” particle’s behavior – even if the two particles were light years apart. Surely QM must be faulty if it entailed such inadmissible effects.
For years, that 1935 paper intrigued philosophers but was (at best) ignored by physicists…until philosopher/physicist Abner Shimony happened on an unpublished 1963 paper by theorist John Bell suggesting the possibility of actually testing Einstein’s entanglement prediction, and set off a long series of experiments that have seemingly shown that Einstein was correct in his deduction but wrong in his conclusion. In this course we’ll examine more closely the history sketched above and the recent experiments leading to what is now called by some “the second quantum revolution.”
Our text will be The Age of Entanglement: When Quantum Physics Was Reborn, by Louisa Gilder (Vintage, 2008, paperback; list price $17.95). This is an unusual book, a sort of “historical novel” constructed almost entirely using extensive quotations from the participants in the story. This seemed implausible when I first heard of it, but actually reading the book convinced me that Gilder does an excellent job, well documented and engagingly written in a non-mathematical style for a general audience. We’ll read the entire book, in chunks that average about 40 pages a week.
Classes will consist mainly of informal lectures, easily interrupted by student questions and comments. There will be occasional demonstrations. Most of the class time will be devoted to discussing the relevant ideas and results in ways intended to clarify and expand on the week’s readings. Below is a provisional schedule; in the event of changes, a revised version will be distributed shortly before the first class.
Class Topics Reading (pages)
Jan. 9 The first quantum ideas 3-31
Max Planck quantizes energy
Albert Einstein quantizes light waves into photons
Jan. 16 Early quantum theories 32-73
Neils Bohr quantizes the atom; failure of causality
Matter waves, quantum spin
Wolfgang Pauli’s “exclusion principle”
Jan. 23 The “final” quantum theory; interpretations and objections 74-122
Werner Heisenberg’s matrix theory, Erwin Schrodinger’s wave equation
Max Born’s probability interpretation
Waves vs particles; Bohr’s “complementarity principle”
Indeterminacy vs causality; does God play dice?
Jan. 30 Hidden variables and EPR 123-177
Einstein’s “light box” argument and Bohr’s challenge
Schrodinger‘s “cat paradox”: the role of observation
Einstein, Podolsky, Rosen (EPR) “paradox”: quantum theory is “incomplete”
John von Neumann’s “no-hidden-variables proof”
Feb. 6 David Bohm’s alternative theory 181-230
His textbook on conventional quantum theory
His hidden variables theory (after exposing von Neumann’s error)
Rejection/ignoring by physics establishment
Feb. 13 Basic experimental tests of entanglement 233-281
John Bell’s inequality: quantum theory vs hidden variables
First tests, using photon polarizations (John Clauser/Stuart Freedman)
Feb. 20 Further quantum theory tests 282-315
Anton Zeilinger: 3-particle entanglement
Use of entanglement for secure (no eavesdropping) data transmission
Feb. 27 More experiments and questions 316-337
Alain Aspect demonstrates entanglement over 10 km
Reflections on current state of quantum theory
Note to any graduates of the Quantum Reality course (Winters 2015 and 2016) considering enrollment here:
In this course (Quantum Entanglement) there will be a fair amount of overlap with that earlier course, as can be seen from the topics listed above. The point of view and the depth of treatment here, however, will be different (less detail on the history of quantum theory; more emphasis on entanglement, recent experiments, and applications).