Quantum theory from quantum information? (What would Feynman say?)
Cambridge, Massachusetts (USA)
For the talk slides, see Slides
For the talk video, see Video

How did the field of quantum information begin? To my mind, it was when John Wheeler formed his little group of students and postdocs at the University of Texas in the early 1980s. David Deutsch (first quantum algorithms), Benjamin Schumacher (inventor of the qubit), William Wootters (no-cloning theorem, later quantum teleportation), and Wojciech Zurek (quantum decoherence) were all there. Even Richard Feynman (father of quantum computation) visited once. It was because Wheeler had a single-minded purpose. Of every student who walked into his office ---even the first-year undergraduate--- Wheeler would implore: “Give an information theoretic derivation of quantum theory!” He saw that as the only way to get true understanding of “the quantum.”
In this talk, I will outline how Wheeler’s old hope is still bearing fruit in the context of Quantum Bayesianism (or QBism). Particularly, that context points naturally to a study of a mysterious structure in Hilbert space called the Symmetric Information Complete (SIC) quantum measurement. When these structures exist (and it seems they do for all finite dimensions, though no one has proven it!) they give a very clean way of writing the Born rule in purely probabilistic terms. This gives the hope that all the mathematical structure of quantum theory might be derivable from one very basic gedankenexperiment. It’s not the double-slit experiment that Feynman argued for in his Feynman Lectures, but one might still appeal to his intuition and hope, “In reality, [this new scenario] contains the only mystery [of quantum mechanics].”