Quantum categories for quantum logic

Giovanni Cinà

This thesis aims at connecting the two research programs known as Categorical Quantum Mechanics and Dynamic Quantum Logic. This is achieved in three steps. First we define a procedure to extract a Modal Logic frame from a small category and a functor into the category of sets and relations. Second, we extend such methodology to locally small categories. Third, we apply it to the category of finite-dimensional Hilbert spaces to recover the semantics of Dynamic Quantum Logic. This process prompts new lines of research. At a general level, we study some logics arising from wide classes of small categories. In the case of Hilbert spaces, we investigate how to obtain richer semantics, containing probabilistic information. We design a logic for this semantics and prove that, via translation, it preserves the validities of Dynamic Quantum Logic.

David Finkelstein

Chris Heunen

We consider categorical logic on the category of Hilbert spaces. More generally, in fact, any pre-Hilbert category suffices. We characterise closed subobjects, and prove that they form orthomodular lattices. This shows that quantum logic is just an incarnation of categorical logic, enabling us to establish an existential quantifier for quantum logic, and conclude that there cannot be a universal quantifier.

Thomas A. Brody

Peter Mittelstaedt

Peter Hines, Samuel L. Braunstein

It is well known that the “quantum logic” approach to the foundations of quantum mechanics is based on the subspace ordering of projectors on a Hilbert space. In this paper, we show that this is a special case of an ordering on partial isometries, introduced by Halmos and McLaughlin. Partial isometries have a natural physical interpretation, however, they are notoriously not closed under composition. In order to take a categorical approach, we demonstrate that the Halmos-McLaughlin partial ordering, together with tools from both categorical logic and inverse categories, allows us to form a category of partial isometries. This category can reasonably be considered a “categorification” of quantum logic – we therefore compare this category with Abramsky and Coecke's “compact closed categories” approach to foundations and with the “monoidal closed categories” view of categorical logic. This comparison illustrates a fundamental incompatibility between these two distinct approaches to the foundations of quantum mechanics. 9.1 Introduction As early as 1936, von Neumann and Birkhoff proposed treating projectors on Hilbert space as propositions about quantum systems (Birkhoff and von Neumann 1936), by direct analogy with classical order-theoretic approaches to logic. Boolean lattices arise as the Lindenbaum-Tarski algebras of propositional logics, and as the set of all projectors on a Hilbert space also forms an orthocomplemented lattice, the operations meet, join , and complement were analogously interpreted as the logical connectives conjunction, disjunction , and negation .