Letters to Bill Wootters

• Published in: Coming of Age With Quantum Information pp. 473 - 482
• Main Author: Fuchs, Christopher A.
• Format: Book Chapter
• Language: English
• Published: United Kingdom Cambridge University Press 06.01.2011
• Subjects: Philosophy of science; Quantum physics (quantum mechanics & quantum field theory)
• ISBN: 0521199263; 9780521199261
• DOI: 10.1017/CBO9780511762789.035

October 1997, and to Asher Peres, “Premonition?”I was awakened this morning just in the middle of a complicated dream. I only remember very fuzzy fragments, but there is one in particular that I thought you two would enjoy hearing about. Someone walked up and handed me a newspaper clipping. The headline read, “Bill Wootters and World Renowned Teleporter Asher Peres Attain New Heights.” I didn't see the article, but the headline was accompanied by a picture of you two both wearing lederhosen and Alpine hats, smiling at the camera!!July 1998, “Quantum Giggles”I'm sitting at a little sidewalk cafe in Benasque, Spain thinking of you and all your efforts to find a compelling structure underneath quantum mechanics.It's strange, but for me this has turned out to be a very foundation-oriented conference. Carl Caves and I have been working to construct a quantum version of de Finetti's theorem in classical probability theory. de Finetti's theorem gives the “subjectivist” a way to interpret an “unknown probability” within his framework: probability distributions over the probability simplex are nothing more than shorthand for a certain kind of probability assignment (called “exchangeable”) over a large multi-trial space. What is an unknown quantum state? If you take quantum states to be states of knowledge, as we do, then an unknown quantum state is a troublesome concept. We think that it can be fixed up in roughly the same way – one just has to identify the right notion of an “exchangeable density operator.”