Characterizing quantum theory in terms of information-theoretic constraints

∗Rob Clifton died of cancer on July 31, 2002, while we were working on this project. The final version of the paper reflects his substantial input to an earlier draft, and extensive mutual discussions and correspon-dence. 1 We show that three fundamental information-theoretic constraints—the impossibility of superluminal information transfer between two physical systems by performing measurements on one of them, the impossibility of broadcasting the information contained in an unknown physical state, and the impossibility of unconditionally secure bit commitment—suffice to en-tail that the observables and state space of a physical theory are quantum-mechanical. We demonstrate the converse derivation in part, and consider the implications of alternative answers to a remaining open question abou