12 research outputs found
Feasibility of loophole-free nonlocality tests with a single photon
Recently much interest has been directed towards designing setups that
achieve realistic loss thresholds for decisive tests of local realism, in
particular in the optical regime. We analyse the feasibility of such Bell tests
based on a W-state shared between multiple parties, which can be realised for
example by a single photon shared between spatial modes. We develop a general
error model to obtain thresholds on the efficiencies required to violate local
realism, and also consider two concrete optical measurement schemes.Comment: 8 pages, 5 figure
Exploring the Local Orthogonality Principle
Nonlocality is arguably one of the most fundamental and counterintuitive
aspects of quantum theory. Nonlocal correlations could, however, be even more
nonlocal than quantum theory allows, while still complying with basic physical
principles such as no-signaling. So why is quantum mechanics not as nonlocal as
it could be? Are there other physical or information-theoretic principles which
prohibit this? So far, the proposed answers to this question have been only
partially successful, partly because they are lacking genuinely multipartite
formulations. In Nat. Comm. 4, 2263 (2013) we introduced the principle of Local
Orthogonality (LO), an intrinsically multipartite principle which is satisfied
by quantum mechanics but is violated by non-physical correlations.
Here we further explore the LO principle, presenting new results and
explaining some of its subtleties. In particular, we show that the set of
no-signaling boxes satisfying LO is closed under wirings, present a
classification of all LO inequalities in certain scenarios, show that all
extremal tripartite boxes with two binary measurements per party violate LO,
and explain the connection between LO inequalities and unextendible product
bases.Comment: Typos corrected; data files uploade
Robust nonlocality tests with displacement-based measurements
Lately, much interest has been directed towards designing setups that achieve
decisive tests of local realism. Here we present Bell tests with measurements
based on linear optical displacements and single-photon detection. The scheme
displays good tolerance to loss. In particular, for entangled squeezed states,
we find thresholds compatible with current efficiencies of detectors and
sources. Furthermore, the scheme is easily extendible to any number of
observers, allowing observation of multipartite nonlocality for a single photon
shared among multiple modes. We also consider the case of atom-photon
entanglement, where the loss threshold can be lowered further, as well as local
filters compensating transmission and coupling inefficiencies at the source.Comment: 5 pages, 2 figures, significant content changes from v1, titled
update
Evolution of non-kin cooperation:social assortment by cooperative phenotype in guppies
© 2019 The Authors. Cooperation among non-kin constitutes a conundrum for evolutionary biology. Theory suggests that non-kin cooperation can evolve if individuals differ consistently in their cooperative phenotypes and assort socially by these, such that cooperative individuals interact predominantly with one another. However, our knowledge of the role of cooperative phenotypes in the social structuring of real-world animal populations is minimal. In this study, we investigated cooperative phenotypes and their link to social structure in wild Trinidadian guppies (Poecilia reticulata). We first investigated whether wild guppies are repeatable in their individual levels of cooperativeness (i.e. have cooperative phenotypes) and found evidence for this in seven out of eight populations, a result which was mostly driven by females. We then examined the social network structure of one of these populations where the expected fitness impact of cooperative contexts is relatively high, and found assortment by cooperativeness, but not by genetic relatedness. By contrast, and in accordance with our expectations, we did not find assortment by cooperativeness in a population where the expected fitness impact of cooperative contexts is lower. Our results provide empirical support for current theory and suggest that assortment by cooperativeness is important for the evolution and persistence of non-kin cooperation in real-world populations