22,845 research outputs found
Higher-order interference in extensions of quantum theory
Quantum interference lies at the heart of several quantum computational
speed-ups and provides a striking example of a phenomenon with no classical
counterpart. An intriguing feature of quantum interference arises in a three
slit experiment. In this set-up, the interference pattern can be written in
terms of the two and one slit patterns obtained by blocking some of the slits.
This is in stark contrast with the standard two slit experiment, where the
interference pattern is irreducible. This was first noted by Rafael Sorkin, who
asked why quantum theory only exhibits irreducible interference in the two slit
experiment. One approach to this problem is to compare the predictions of
quantum theory to those of operationally-defined `foil' theories, in the hope
of determining whether theories exhibiting higher-order interference suffer
from pathological--or at least undesirable--features. In this paper two
proposed extensions of quantum theory are considered: the theory of Density
Cubes proposed by Dakic et al., which has been shown to exhibit irreducible
interference in the three slit set-up, and the Quartic Quantum Theory of
Zyczkowski. The theory of Density Cubes will be shown to provide an advantage
over quantum theory in a certain computational task and to posses a
well-defined mechanism which leads to the emergence of quantum theory. Despite
this, the axioms used to define Density Cubes will be shown to be insufficient
to uniquely characterise the theory. In comparison, Quartic Quantum Theory is
well-defined and we show that it exhibits irreducible interference to all
orders. This feature of the theory is argued not to be a genuine phenomenon,
but to arise from an ambiguity in the current definition of higher-order
interference. To understand why quantum theory has limited interference
therefore, a new operational definition of higher-order interference is needed.Comment: Updated in response to referee comments. 17 pages. Comments welcom
Deriving Grover's lower bound from simple physical principles
Grover's algorithm constitutes the optimal quantum solution to the search
problem and provides a quadratic speed-up over all possible classical search
algorithms. Quantum interference between computational paths has been posited
as a key resource behind this computational speed-up. However there is a limit
to this interference, at most pairs of paths can ever interact in a fundamental
way. Could more interference imply more computational power? Sorkin has defined
a hierarchy of possible interference behaviours---currently under experimental
investigation---where classical theory is at the first level of the hierarchy
and quantum theory belongs to the second. Informally, the order in the
hierarchy corresponds to the number of paths that have an irreducible
interaction in a multi-slit experiment. In this work, we consider how Grover's
speed-up depends on the order of interference in a theory. Surprisingly, we
show that the quadratic lower bound holds regardless of the order of
interference. Thus, at least from the point of view of the search problem,
post-quantum interference does not imply a computational speed-up over quantum
theory.Comment: Updated title and exposition in response to referee comments. 6+2
pages, 5 figure
A digital control system for high level acoustic noise generation
As part of the modernization of the Acoustic Test Facility at Lockheed Missiles and Space Company, Sunnyvale, a digital acoustic control system was designed and built. The requirements imposed by Lockheed on the control system and the degree to which those requirements were met are discussed. Acceptance test results as well as some of the features of the digital control system not found in traditional manual control systems are discussed
Oracles and query lower bounds in generalised probabilistic theories
We investigate the connection between interference and computational power
within the operationally defined framework of generalised probabilistic
theories. To compare the computational abilities of different theories within
this framework we show that any theory satisfying three natural physical
principles possess a well-defined oracle model. Indeed, we prove a subroutine
theorem for oracles in such theories which is a necessary condition for the
oracle to be well-defined. The three principles are: causality (roughly, no
signalling from the future), purification (each mixed state arises as the
marginal of a pure state of a larger system), and strong symmetry existence of
non-trivial reversible transformations). Sorkin has defined a hierarchy of
conceivable interference behaviours, where the order in the hierarchy
corresponds to the number of paths that have an irreducible interaction in a
multi-slit experiment. Given our oracle model, we show that if a classical
computer requires at least n queries to solve a learning problem, then the
corresponding lower bound in theories lying at the kth level of Sorkin's
hierarchy is n/k. Hence, lower bounds on the number of queries to a quantum
oracle needed to solve certain problems are not optimal in the space of all
generalised probabilistic theories, although it is not yet known whether the
optimal bounds are achievable in general. Hence searches for higher-order
interference are not only foundationally motivated, but constitute a search for
a computational resource beyond that offered by quantum computation.Comment: 17+7 pages. Comments Welcome. Published in special issue
"Foundational Aspects of Quantum Information" in Foundations of Physic
Telecommunications and economic growth: an empirical analysis of sub-saharan Africa
We examine the effect on economic growth of mobile cellular phones in sub-Saharan Africa where a marked asymmetry is present between land-line penetration and mobile telecommunications expansion. This study extends previous ones along two important dimensions. First, we allow for the potential endogeneity between economic growth and telecommunications expansion by employing a special linear generalized method of moments (GMM) estimator. Second, we explicitly model for varying degrees of substitutability between mobile cellular and land-line telephony, so that greater expansion of mobile telecommunications can have a different impact whenever the level of land-line penetration differs. We find that mobile cellular phone expansion is an important determinant of the rate of economic growth in Sub-Saharan Africa. Moreover, we find that the contribution of mobile cellular phones to economic growth has been growing in importance in the region, and that the marginal impact of mobile telecommunication services is even greater wherever land-line phones are rare. Given the low cost of mobile telecommunications technology relative to other broad infrastructure projects, especially land-line infrastructure, we advocate that mobile telecommunication services be encouraged in the area.
Microgravity combustion of dust suspensions
Unlike the combustion of homogeneous gas mixtures, there are practically no reliable fundamental data (i.e., laminar burning velocity, flammability limits, quenching distance, minimum ignition energy) for the combustion of heterogeneous dust suspensions. Even the equilibrium thermodynamic data such as the constant pressure volume combustion pressure and the constant pressure adiabatic flame temperature are not accurately known for dust mixtures. This is mainly due to the problem of gravity sedimentation. In normal gravity, turbulence, convective flow, electric and acoustic fields are required to maintain a dust in suspension. These external influences have a dominating effect on the combustion processes. Microgravity offers a unique environment where a quiescent dust cloud can in principle be maintained for a sufficiently long duration for almost all combustion experiments (dust suspensions are inherently unstable due to Brownian motion and particle aggregation). Thus, the microgravity duration provided by drop towers, parabolic flights, and the space shuttle, can all be exploited for different kinds of dust combustion experiments. The present paper describes some recent studies on microgravity combustion of dust suspension carried out on the KC-135 and the Caravelle aircraft. The results reported are obtained from three parabolic flight campaigns
Ruling out higher-order interference from purity principles
As first noted by Rafael Sorkin, there is a limit to quantum interference.
The interference pattern formed in a multi-slit experiment is a function of the
interference patterns formed between pairs of slits, there are no genuinely new
features resulting from considering three slits instead of two. Sorkin has
introduced a hierarchy of mathematically conceivable higher-order interference
behaviours, where classical theory lies at the first level of this hierarchy
and quantum theory theory at the second. Informally, the order in this
hierarchy corresponds to the number of slits on which the interference pattern
has an irreducible dependence. Many authors have wondered why quantum
interference is limited to the second level of this hierarchy. Does the
existence of higher-order interference violate some natural physical principle
that we believe should be fundamental? In the current work we show that such
principles can be found which limit interference behaviour to second-order, or
"quantum-like", interference, but that do not restrict us to the entire quantum
formalism. We work within the operational framework of generalised
probabilistic theories, and prove that any theory satisfying Causality, Purity
Preservation, Pure Sharpness, and Purification---four principles that formalise
the fundamental character of purity in nature---exhibits at most second-order
interference. Hence these theories are, at least conceptually, very "close" to
quantum theory. Along the way we show that systems in such theories correspond
to Euclidean Jordan algebras. Hence, they are self-dual and, moreover,
multi-slit experiments in such theories are described by pure projectors.Comment: 18+8 pages. Comments welcome. v2: Minor correction to Lemma 5.1, main
results are unchange
Eccomi pronto : implementation of a Socio-Emotional Development curriculum in a South Korean elementary school
‘Eccomi Pronto’ (EP), an elementary school socio-emotional learning curriculum that
was originally developed and evaluated in Italy was translated in Korean and
implemented and evaluated in 4th grade classrooms of a primary school in South Korea.
Qualitative data from teachers indicated that EP improved the self-reflection and selfdirection
of students, resulted in pedagogically useful insights into the psychological
functioning of students, and enhanced the quality of teacher-student interaction.
However, statistically significant changes in students’ engaged, academic behavior (as
measured by an 8-item survey) were not noted. Teachers reported that the core of the EP
curriculum was appropriate for the South Korean educational context. Teachers also
recommended modifications in the follow-up learning activities to make these activities
more consistent with South Korean education practices.peer-reviewe
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