Titles and Abstracts

The role of measurement in quantum theory remains both perplexing and controversial, especially for no-collapse interpretations (e.g., many-worlds, or the ``existential'' view). One of the outstanding challenges in these frameworks is to explain preferred bases -i.e., why measurements and observations always break unitary invariance. In this talk, I'll present a framework, motivated by information theory, to address this question -then use it to derive a simple answer to the question ``Why do measurements yield classical information, about a single basis?'' A measurement is any interaction causing knowledge acquisition (development of correlations between observer and observed). Quantum theory supports two kinds of measurements (predictive and retrodictive), in which the observer learns either about the future or the past of the observed system. Generalizing a recent result, which classified the kinds of information that a quantum process can preserve, allows us to analyze both kinds of measurement, yielding a unified answer to the question ``What can one quantum system know about another?'' As an application, I'll prove that that one system (e.g. an apparatus or observer) can have non-classical knowledge about another system's future OR its past -but not both. Eric Cavalcanti: Steering, predictability and other concepts of experimental metaphysics ABSTRACT: Since the seminal work of Bell, inspired by the paradox of Einstein, Podolsky and Rosen, many assumptions and concepts until then considered "metaphysical" were shown to have experimental consequences. In this talk I will review a few of these concepts and show some new results. Since the seminal work of Bell, inspired by the paradox of Einstein, Podolsky and Rosen, many assumptions and concepts until then considered "metaphysical" were shown to have experimental consequences. In this talk I will review a few of these concepts and show some new results. First, I argue that a formalisation of local causality and completeness, in the spirit of Bell, leads to either the notion of quantum separability or to a local hidden state (LHS) model, depending on whether one or both of Alice's and Bob's subsystems are given a quantum description. I therefore argue that the LHS model, the violation of which is called Steering [Phys. Rev. Lett. 98, 140402, (2007)], is the most general formalisation of the EPR paradox, and show that previously known criteria, as well as new ones, can be directly derived from that assumption. Implications to arguments commonly used to defend the epistemic view of quantum states will be discussed. On another of Einstein's contentions with Bohr, I will propose that in the 1927 Solvay conference, Bohr's reply to Einstein could have been stronger. At that conference, Einstein tried to attack not simply the completeness, but the empirical correctness of quantum theory, by attempting to evade Heisenberg's Uncertainty Principle (HUP), which implies that quantum phenomena are irreducibly unpredictable. Bohr's reply established the consistency of the HUP -but not necessarily its correctness -by showing that a consistent application of it does not allow contradictions. I will propose a result that goes beyond that: by carefully defining predictability as distinct from determinism, and considering the (observed) Bell violations, we can show that if relativistic invariance is assumed, Nature must be irreducibly unpredictable. Carl Caves: Should we think of quantum probabilities as Bayesian probabilities? ABSTRACT: Should we? Seems unlikely, since quantum probabilities are part of the fabric of quantum mechanics, the framework for all physical law. Yet all classical probabilities are Bayesian, never dictated by facts, and so it is with all quantum probabilities, suggesting that they, too, should be thought of as Should we? Seems unlikely, since quantum probabilities are part of the fabric of quantum mechanics, the framework for all physical law. Yet all classical probabilities are Bayesian, never dictated by facts, and so it is with all quantum probabilities, suggesting that they, too, should be thought of as Bayesian. I will compare and contrast classical and quantum probabilities and conclude with a stab at the ontology behind quantum mechanics, which lies not in the framework of quantum states, which we use to make inferences and predictions, but rather in the physical laws themselves.