35 research outputs found
On the Cohomology of Contextuality
Recent work by Abramsky and Brandenburger used sheaf theory to give a
mathematical formulation of non-locality and contextuality. By adopting this
viewpoint, it has been possible to define cohomological obstructions to the
existence of global sections. In the present work, we illustrate new insights
into different aspects of this theory. We shed light on the power of detection
of the cohomological obstruction by showing that it is not a complete invariant
for strong contextuality even under symmetry and connectedness restrictions on
the measurement cover, disproving a previous conjecture. We generalise
obstructions to higher cohomology groups and show that they give rise to a
refinement of the notion of cohomological contextuality: different "levels" of
contextuality are organised in a hierarchy of logical implications. Finally, we
present an alternative description of the first cohomology group in terms of
torsors, resulting in a new interpretation of the cohomological obstructions.Comment: In Proceedings QPL 2016, arXiv:1701.0024
Putting the Semantics into Semantic Versioning
The long-standing aspiration for software reuse has made astonishing strides
in the past few years. Many modern software development ecosystems now come
with rich sets of publicly-available components contributed by the community.
Downstream developers can leverage these upstream components, boosting their
productivity.
However, components evolve at their own pace. This imposes obligations on and
yields benefits for downstream developers, especially since changes can be
breaking, requiring additional downstream work to adapt to. Upgrading too late
leaves downstream vulnerable to security issues and missing out on useful
improvements; upgrading too early results in excess work. Semantic versioning
has been proposed as an elegant mechanism to communicate levels of
compatibility, enabling downstream developers to automate dependency upgrades.
While it is questionable whether a version number can adequately characterize
version compatibility in general, we argue that developers would greatly
benefit from tools such as semantic version calculators to help them upgrade
safely. The time is now for the research community to develop such tools: large
component ecosystems exist and are accessible, component interactions have
become observable through automated builds, and recent advances in program
analysis make the development of relevant tools feasible. In particular,
contracts (both traditional and lightweight) are a promising input to semantic
versioning calculators, which can suggest whether an upgrade is likely to be
safe.Comment: to be published as Onward! Essays 202
Efficient Iterative Programs with Distributed Data Collections
Big data programming frameworks have become increasingly important
for the development of applications for which performance and
scalability are critical. In those complex frameworks, optimizing
code by hand is hard and time-consuming, making automated
optimization particularly necessary. In order to automate
optimization, a prerequisite is to find suitable abstractions to
represent programs; for instance, algebras based on monads or
monoids to represent distributed data collections. Currently,
however, such algebras do not represent recursive programs in a way
which allows for analyzing or rewriting them. In this paper, we extend a
monoid algebra with a fixpoint operator for representing recursion
as a first class citizen and show how it enables new optimizations.
Experiments with the Spark platform illustrate performance gains
brought by these systematic optimizations.Comment: 36 page
On monogamy of non-locality and macroscopic averages: examples and preliminary results
We explore a connection between monogamy of non-locality and a weak
macroscopic locality condition: the locality of the average behaviour. These
are revealed by our analysis as being two sides of the same coin.
Moreover, we exhibit a structural reason for both in the case of Bell-type
multipartite scenarios, shedding light on but also generalising the results in
the literature [Ramanathan et al., Phys. Rev. Lett. 107, 060405 (2001);
Pawlowski & Brukner, Phys. Rev. Lett. 102, 030403 (2009)]. More specifically,
we show that, provided the number of particles in each site is large enough
compared to the number of allowed measurement settings, and whatever the
microscopic state of the system, the macroscopic average behaviour is local
realistic, or equivalently, general multipartite monogamy relations hold.
This result relies on a classical mathematical theorem by Vorob'ev [Theory
Probab. Appl. 7(2), 147-163 (1962)] about extending compatible families of
probability distributions defined on the faces of a simplicial complex -- in
the language of the sheaf-theoretic framework of Abramsky & Brandenburger [New
J. Phys. 13, 113036 (2011)], such families correspond to no-signalling
empirical models, and the existence of an extension corresponds to locality or
non-contextuality. Since Vorob'ev's theorem depends solely on the structure of
the simplicial complex, which encodes the compatibility of the measurements,
and not on the specific probability distributions (i.e. the empirical models),
our result about monogamy relations and locality of macroscopic averages holds
not just for quantum theory, but for any empirical model satisfying the
no-signalling condition.
In this extended abstract, we illustrate our approach by working out a couple
of examples, which convey the intuition behind our analysis while keeping the
discussion at an elementary level.Comment: In Proceedings QPL 2014, arXiv:1412.810