148 research outputs found
Quantum Advantage in Information Retrieval
Random access codes have provided many examples of quantum advantage in
communication, but concern only one kind of information retrieval task. We
introduce a related task - the Torpedo Game - and show that it admits greater
quantum advantage than the comparable random access code. Perfect quantum
strategies involving prepare-and-measure protocols with experimentally
accessible three-level systems emerge via analysis in terms of the discrete
Wigner function. The example is leveraged to an operational advantage in a
pacifist version of the strategy game Battleship. We pinpoint a characteristic
of quantum systems that enables quantum advantage in any bounded-memory
information retrieval task. While preparation contextuality has previously been
linked to advantages in random access coding we focus here on a different
characteristic called sequential contextuality. It is shown not only to be
necessary and sufficient for quantum advantage, but also to quantify the degree
of advantage. Our perfect qutrit strategy for the Torpedo Game entails the
strongest type of inconsistency with non-contextual hidden variables, revealing
logical paradoxes with respect to those assumptions.Comment: 15 pages, 11 figures; new presentation, additional figures and
reference
Continuous-variable nonlocality and contextuality
Contextuality is a non-classical behaviour that can be exhibited by quantum
systems. It is increasingly studied for its relationship to
quantum-over-classical advantages in informatic tasks. To date, it has largely
been studied in discrete variable scenarios, where observables take values in
discrete and usually finite sets. Practically, on the other hand,
continuous-variable scenarios offer some of the most promising candidates for
implementing quantum computations and informatic protocols. Here we set out a
framework for treating contextuality in continuous-variable scenarios. It is
shown that the Fine--Abramsky--Brandenburger theorem extends to this setting,
an important consequence of which is that nonlocality can be viewed as a
special case of contextuality, as in the discrete case. The contextual
fraction, a quantifiable measure of contextuality that bears a precise
relationship to Bell inequality violations and quantum advantages, can also be
defined in this setting. It is shown to be a non-increasing monotone with
respect to classical operations that include binning to discretise data.
Finally, we consider how the contextual fraction can be formulated as an
infinite linear program, and calculated with increasing accuracy using
semi-definite programming approximations.Comment: 27 pages including 6 pages supplemental material, 2 figure
Corrected Bell and Noncontextuality Inequalities for Realistic Experiments
Contextuality is a feature of quantum correlations. It is crucial from a
foundational perspective as a nonclassical phenomenon, and from an applied
perspective as a resource for quantum advantage. It is commonly defined in
terms of hidden variables, for which it forces a contradiction with the
assumptions of parameter-independence and determinism. The former can be
justified by the empirical property of non-signalling or non-disturbance, and
the latter by the empirical property of measurement sharpness. However, in
realistic experiments neither empirical property holds exactly, which leads to
possible objections to contextuality as a form of nonclassicality, and
potential vulnerabilities for supposed quantum advantages. We introduce
measures to quantify both properties, and introduce quantified relaxations of
the corresponding assumptions. We prove the continuity of a known measure of
contextuality, the contextual fraction, which ensures its robustness to noise.
We then bound the extent to which these relaxations can account for
contextuality, via corrections terms to the contextual fraction (or to any
noncontextuality inequality), culminating in a notion of genuine contextuality,
which is robust to experimental imperfections. We then show that our result is
general enough to apply or relate to a variety of established results and
experimental setups.Comment: 20 pages + 14 pages of appendices, 3 figure
Functional brain neuroimaging-guided repetitive transcranial magnetic stimulation in neurodevelopmental disorders: The case of a schizencephaly-related spastic dystonia
International audienceSpastic dystonia is defined as tonic involuntary muscle activation at rest superimposed over spastic paresis [1]. It occurs in different pathological conditions, ranging from dopamine-dependent dystonia [2] to post-stroke deforming spastic hemiparesis [1]. Even though important burden is associated to spastic dystonia, therapeutic options are scarce and mostly limited to intramuscular botulinum toxin injection and surgical partial nerve section. Repetitive transcranial magnetic stimulation (rTMS) has been proposed as an interesting therapeutic option, but with inconsistent results [3]. We suggest that optimized targeting based on functional brain imaging could enhance the results of rTMS in schizencephaly-related dystonia and improve our knowledge about the technical procedure to become more widely applicable in neurodevelopmental disorders
Do anti-poverty programs sway voters? Experimental evidence from Uganda
High-impact policies may not lead to support for the political party that introduces them. In 2008, Uganda's government encouraged groups of youth to submit proposals to start enterprises. Of 535 eligible groups, a random 265 received grants of nearly $400 per person. Prior work showed that after four years, the Youth Opportunities Program raised employment by 17% and earnings by 38%. Here we show that recipients were no more likely to support the ruling party in elections. Rather, recipients slightly increased campaigning and voting for the opposition. Potential mechanisms include program misattribution, group socialization, and financial independence freeing voters from transactional voting
On differential rotation and overshooting in solar-like stars
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this record.We seek to characterize how the change of global rotation rate influences the overall dynamics and large scale flows arising in the convective envelopes of stars covering stellar spectral types from early G to late K. We do so through numerical simulations with the ASH code, where we consider stellar convective envelopes coupled to a radiative interior with various global properties. As solar-like stars spin down over the course of their main sequence evolution, such change must have a direct impact on their dynamics and rotation state. We indeed find that three main states of rotation may exist for a given star: anti-solar-like (fast poles, slow equator), solar-like (fast equator, slow poles), or a cylindrical rotation profile. Under increasingly strict rotational constraints, the latter profile can further evolve into a Jupiter-like profile, with alternating prograde and retrograde zonal jets. We have further assessed how far the convection and meridional flows overshoot into the radiative zone and investigated the morphology of the established tachocline. Using simple mixing length arguments, we are able to construct a scaling of the fluid Rossby number , which we calibrate based on our 3-D ASH simulations. We can use this scaling to map the behavior of differential rotation versus the global parameters of stellar mass and rotation rate. Finally, we isolate a region on this map () where we posit that stars with an anti-solar differential rotation may exist in order to encourage observers to hunt for such targets.We acknowledge funding by ERC STARS2 207430 grant, ANR Blanc Toupies SIMI5-6 020 01, INSU/PNST, CNES SolarOrbiter, PLATO and GOLF grants, FP7 SpaceInn 312844 grant, and NASA grants NNX11AJ36G, NNX13AG18G and NNX16AC92G. K. C. Augustson is funded through the
ERC SPIRE 647383 grant. A. Strugarek acknowledges support from the Canadian Institute of Theoretical Astrophysics (National Fellow), from Canadas Natural Sciences and Engineering Research Council and from CNES postdoctoral fellowship
Perceval: A Software Platform for Discrete Variable Photonic Quantum Computing
We introduce Perceval, an evolutive open-source software platform for
simulating and interfacing with discrete variable photonic quantum computers,
and describe its main features and components. Its Python front-end allows
photonic circuits to be composed from basic photonic building blocks like
photon sources, beam splitters, phase shifters and detectors. A variety of
computational back-ends are available and optimised for different use-cases.
These use state-of-the-art simulation techniques covering both weak simulation,
or sampling, and strong simulation. We give examples of Perceval in action by
reproducing a variety of photonic experiments and simulating photonic
implementations of a range of quantum algorithms, from Grover's and Shor's to
examples of quantum machine learning. Perceval is intended to be a useful
toolkit both for experimentalists wishing to easily model, design, simulate, or
optimise a discrete variable photonic experiment, and for theoreticians wishing
to design algorithms and applications for discrete-variable photonic quantum
computing platforms
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