21 research outputs found
Speakable in quantum mechanics: babbling on
This paper consists of a short version of the derivation of the
intuitionistic quantum logic L_QM (which was originally introduced by Caspers,
Heunen, Landsman and Spitters). The elaboration consists of extending this
logic to a classical logic CL_QM. Some first steps are then taken towards
setting up a probabilistic framework based on CL_QM in terms of R\'enyi's
conditional probability spaces. Comparisons are then made with the traditional
framework for quantum probabilities.Comment: In Proceedings QPL 2012, arXiv:1407.842
Topos Quantum Logic and Mixed States
The topos approach to the formulation of physical theories includes a new
form of quantum logic. We present this topos quantum logic, including some new
results, and compare it to standard quantum logic, all with an eye to
conceptual issues. In particular, we show that topos quantum logic is
distributive, multi-valued, contextual and intuitionistic. It incorporates
superposition without being based on linear structures, has a built-in form of
coarse-graining which automatically avoids interpretational problems usually
associated with the conjunction of propositions about incompatible physical
quantities, and provides a material implication that is lacking from standard
quantum logic. Importantly, topos quantum logic comes with a clear geometrical
underpinning. The representation of pure states and truth-value assignments are
discussed. It is briefly shown how mixed states fit into this approach.Comment: 25 pages; to appear in Electronic Notes in Theoretical Computer
Science (6th Workshop on Quantum Physics and Logic, QPL VI, Oxford, 8.--9.
April 2009), eds. B. Coecke, P. Panangaden, P. Selinger (2010
Bohrification of operator algebras and quantum logic
Following Birkhoff and von Neumann, quantum logic has traditionally been
based on the lattice of closed linear subspaces of some Hilbert space, or, more
generally, on the lattice of projections in a von Neumann algebra A.
Unfortunately, the logical interpretation of these lattices is impaired by
their nondistributivity and by various other problems. We show that a possible
resolution of these difficulties, suggested by the ideas of Bohr, emerges if
instead of single projections one considers elementary propositions to be
families of projections indexed by a partially ordered set C(A) of appropriate
commutative subalgebras of A. In fact, to achieve both maximal generality and
ease of use within topos theory, we assume that A is a so-called Rickart
C*-algebra and that C(A) consists of all unital commutative Rickart
C*-subalgebras of A. Such families of projections form a Heyting algebra in a
natural way, so that the associated propositional logic is intuitionistic:
distributivity is recovered at the expense of the law of the excluded middle.
Subsequently, generalizing an earlier computation for n-by-n matrices, we
prove that the Heyting algebra thus associated to A arises as a basis for the
internal Gelfand spectrum (in the sense of Banaschewski-Mulvey) of the
"Bohrification" of A, which is a commutative Rickart C*-algebra in the topos of
functors from C(A) to the category of sets. We explain the relationship of this
construction to partial Boolean algebras and Bruns-Lakser completions. Finally,
we establish a connection between probability measure on the lattice of
projections on a Hilbert space H and probability valuations on the internal
Gelfand spectrum of A for A = B(H).Comment: 31 page