4,819 research outputs found
Negativity and contextuality are equivalent notions of nonclassicality
Two notions of nonclassicality that have been investigated intensively are:
(i) negativity, that is, the need to posit negative values when representing
quantum states by quasiprobability distributions such as the Wigner
representation, and (ii) contextuality, that is, the impossibility of a
noncontextual hidden variable model of quantum theory (also known as the
Bell-Kochen-Specker theorem). Although both of these notions were meant to
characterize the conditions under which a classical explanation cannot be
provided, we demonstrate that they prove inadequate to the task and we argue
for a particular way of generalizing and revising them. With the refined
version of each in hand, it becomes apparent that they are in fact one and the
same. We also demonstrate the impossibility of noncontextuality or
nonnegativity in quantum theory with a novel proof that is symmetric in its
treatment of measurements and preparations.Comment: 5 pages, published version (modulo some supplementary material
Persistence of Tripartite Nonlocality for Non-inertial Observers
We consider the behaviour of bipartite and tripartite non-locality between
fermionic entangled states shared by observers, one of whom uniformly
accelerates. We find that while fermionic entanglement persists for arbitrarily
large acceleration, the Bell/CHSH inequalities cannot be violated for
sufficiently large but finite acceleration. However the Svetlichny inequality,
which is a measure of genuine tripartite non-locality, can be violated for any
finite value of the acceleration.Comment: 4 pages, pdflatex, 2 figure
Long-range quantum entanglement in noisy cluster states
We describe a phase transition for long-range entanglement in a
three-dimensional cluster state affected by noise. The partially decohered
state is modeled by the thermal state of a suitable Hamiltonian. We find that
the temperature at which the entanglement length changes from infinite to
finite is nonzero. We give an upper and lower bound to this transition
temperature.Comment: 7 page
Pre- and Post-selection paradoxes and contextuality in quantum mechanics
Many seemingly paradoxical effects are known in the predictions for outcomes
of intermediate measurements made on pre- and post-selected quantum systems.
Despite appearances, these effects do not demonstrate the impossibility of a
noncontextual hidden variable theory, since an explanation in terms of
measurement-disturbance is possible. Nonetheless, we show that for every
paradoxical effect wherein all the pre- and post- selected probabilities are 0
or 1 and the pre- and post-selected states are nonorthogonal, there is an
associated proof of contextuality. This proof is obtained by considering all
the measurements involved in the paradoxical effect -- the pre-selection, the
post-selection, and the alternative possible intermediate measurements -- as
alternative possible measurements at a single time.Comment: 5 pages, 1 figure. Submitted to Phys. Rev. Lett. v2.0 revised in the
light of referee comments, results unchange
Imaging with a small number of photons
Low-light-level imaging techniques have application in many diverse fields,
ranging from biological sciences to security. We demonstrate a single-photon
imaging system based on a time-gated inten- sified CCD (ICCD) camera in which
the image of an object can be inferred from very few detected photons. We show
that a ghost-imaging configuration, where the image is obtained from photons
that have never interacted with the object, is a useful approach for obtaining
images with high signal-to-noise ratios. The use of heralded single-photons
ensures that the background counts can be virtually eliminated from the
recorded images. By applying techniques of compressed sensing and associated
image reconstruction, we obtain high-quality images of the object from raw data
comprised of fewer than one detected photon per image pixel.Comment: 9 pages, 4 figure
High-fidelity entanglement swapping with fully independent sources
Entanglement swapping allows to establish entanglement between independent
particles that never interacted nor share any common past. This feature makes
it an integral constituent of quantum repeaters. Here, we demonstrate
entanglement swapping with time-synchronized independent sources with a
fidelity high enough to violate a Clauser-Horne-Shimony-Holt inequality by more
than four standard deviations. The fact that both entangled pairs are created
by fully independent, only electronically connected sources ensures that this
technique is suitable for future long-distance quantum communication
experiments as well as for novel tests on the foundations of quantum physics.Comment: added technical details and extended introduction and conclusion,
slightly modified the abstract, corrected a mistake in the affiliation
ILR Impact Brief - Knowledge, Skills, and Performance: Getting the Most From Team Training
Teams are an integral feature of the American workplace; indeed, more than 80% of the Fortune 500 companies make extensive use of work teams. Action teams, pulled together to carry out a particular time-limited function that requires the specialized expertise of its members, are becoming increasingly common. Researchers have noted that the success of these teams is often thwarted by their lack of information about teamwork in general and their insufficient mastery of basic team competencies. Most organizations train team members for the particular job at hand, so the question arises as to the utility of generic team training. In other words, would imparting knowledge and skills that could be applied in, and adapted to, any number of situations improve outcomes, and if so, what is the mechanism that facilitates this result
A macro-realism inequality for opto-electro-mechanical systems
We show how to apply the Leggett-Garg inequality to opto-electro-mechanical
systems near their quantum ground state. We find that by using a dichotomic
quantum non-demolition measurement (via, e.g., an additional circuit-QED
measurement device) either on the cavity or on the nanomechanical system
itself, the Leggett-Garg inequality is violated. We argue that only
measurements on the mechanical system itself give a truly unambigous violation
of the Leggett-Garg inequality for the mechanical system. In this case, a
violation of the Leggett-Garg inequality indicates physics beyond that of
"macroscopic realism" is occurring in the mechanical system. Finally, we
discuss the difficulties in using unbound non-dichotomic observables with the
Leggett-Garg inequality.Comment: 9 pages, 2 figures. Added additional figure (2b), and associated
conten
The Impact of Task- and Team-Generic Teamwork Skills Training on Team Effectiveness
This study examined the effects of training team members in three task- and teamgeneric teamwork skills: planning and task coordination, collaborative problem solving, and communication. We first examined the degree to which task- and team-generic teamwork skills training impacted team performance on a task unrelated to the content of the training program.We then examined whether the effects of task- and team-generic teamwork skills training on team performance were due to the transfer of skills directly related to planning and task coordination, collaborative problem solving, and communication. Results from 65 four-person project teams indicated that task- and team-generic teamwork skills training led to significantly higher levels of team performance. Results also indicated that the effects of task- and teamgeneric teamwork skills training on team performance were mediated by planning and task coordination and collaborative problem solving behavior. Although communication was positively affected by the task- and team-generic teamwork skills training, it did not mediate the relationship between task- and team-generic teamwork skills training and team performance.Theoretical and practical implications of these results are discussed, as well as possible limitations and directions for future research
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