902 research outputs found
Implications of Teleportation for Nonlocality
Adopting an approach similar to that of Zukowski [Phys. Rev. A 62, 032101
(2000)], we investigate connections between teleportation and nonlocality. We
derive a Bell-type inequality pertaining to the teleportation scenario and show
that it is violated in the case of teleportation using a perfect singlet. We
also investigate teleportation using `Werner states' of the form x P + (1-x)
I/4, where P is the projector corresponding to a singlet state and I is the
identity. We find that our inequality is violated, implying nonlocality, if x >
1/sqrt(2). In addition, we extend Werner's local hidden variable model to
simulation of teleportation with the x = 1/2 Werner state. Thus teleportation
using this state does not involve nonlocality even though the fidelity achieved
is 3/4 which is greater than the `classical limit' of 2/3. Finally, we comment
on a result of Gisin's and offer some philosophical remarks on teleportation
and nonlocality generally.Comment: 10 pages, no figures. Title changed to accord with Phys. Rev. A
version. A note and an extra reference have been added. Journal reference
adde
expansion of maxillary arches with crossbite a systematic review of rcts in the last 12 years
The aim of this study was to review recent randomized clinical trials (RCTs) dealing with the effectiveness of various modalities of orthopaedic/orthodontic expansion of maxillary arches with crossbite and the associated 6 month post retention stability. The study selection criteria included RCTs involving subjects with maxillary deficiency with crossbite, with no limits of age. The authors searched the following electronic databases from 1999 to January 2011: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, LILACS, and WEB of SCIENCE. The search strategy resulted in 12 articles meeting the inclusion criteria. Most of the studies did not meet major methodological requirements; some studies were not relevant because of small sample size, possible bias and unaccounted for confounding variables, lack of blinding in measurements, and deficient statistical methods. Treatment outcomes were different depending on the appliance used, tooth tissue-borne/tooth-borne expanders, bonded semi-rapid maxillary expansion (SRME), or rapid maxillary expansion (RME); in any case, methodological flaws prevent any sound conclusion. Stable results have been measured at the 6 month follow-up after removal of the retention plate in the treated groups in the maxillary intermolar and intercanine distances. Long-term stability results should be assessed. The Consolidated Standards of Reporting Trials (CONSORT) Statement could be helpful in improving the reporting of RCTs
Optical generation of hybrid entangled state via entangling single-photon-added coherent state
We propose a feasible scheme to realize the optical entanglement of
single-photon-added coherent state (SPACS) and show that, besides the Sanders
entangled coherent state, the entangled SPACS also leads to new forms of hybrid
entanglement of quantum Fock state and classical coherent state. We probe the
essential difference of two types of hybrid entangled state (HES). This HES
provides a novel link between the discrete- and the continuous-variable
entanglement in a natural way.Comment: 6 pages, 2 figure
Hidden-variable theorems for real experiments
It has recently been questioned whether the Kochen-Specker theorem is
relevant to real experiments, which by necessity only have finite precision. We
give an affirmative answer to this question by showing how to derive
hidden-variable theorems that apply to real experiments, so that non-contextual
hidden variables can indeed be experimentally disproved. The essential point is
that for the derivation of hidden-variable theorems one does not have to know
which observables are really measured by the apparatus. Predictions can be
derived for observables that are defined in an entirely operational way.Comment: 4 page
3D simulations of vertical displacement events in tokamaks: A benchmark of M3D-C<sup>1</sup>, NIMROD, and JOREK editors-pick
MGP versus Kochen-Specker condition in hidden variables theories
Hidden variables theories for quantum mechanics are usually assumed to
satisfy the KS condition. The Bell-Kochen-Specker theorem then shows that these
theories are necessarily contextual. But the KS condition can be criticized
from an operational viewpoint, which suggests that a weaker condition (MGP)
should be adopted in place of it. This leads one to introduce a class of hidden
parameters theories in which contextuality can, in principle, be avoided, since
the proofs of the Bell-Kochen-Specker theorem break down. A simple model
recently provided by the author for an objective interpretation of quantum
mechanics can be looked at as a noncontextual hidden parameters theory, which
shows that such theories actually exist.Comment: 10 pages, new updated footnotes and quotation
Generalized quantum measurements and local realism
The structure of a local hidden variable model for experiments involving
sequences of measurements rigorously is analyzed. Constraints imposed by local
realism on the conditional probabilities of the outcomes of such measurement
schemes are explicitly derived. The violation of local realism in the case of
``hidden nonlocality'' is illustrated by an operational example.Comment: Revtex, 12 pages; Some modifications of introduction has been made; a
note stating that part of results had been obtained earlier by other authors,
has been added; one postscript figure available at request from
[email protected]
Multi-Prover Commitments Against Non-Signaling Attacks
We reconsider the concept of multi-prover commitments, as introduced in the
late eighties in the seminal work by Ben-Or et al. As was recently shown by
Cr\'{e}peau et al., the security of known two-prover commitment schemes not
only relies on the explicit assumption that the provers cannot communicate, but
also depends on their information processing capabilities. For instance, there
exist schemes that are secure against classical provers but insecure if the
provers have quantum information processing capabilities, and there are schemes
that resist such quantum attacks but become insecure when considering general
so-called non-signaling provers, which are restricted solely by the requirement
that no communication takes place.
This poses the natural question whether there exists a two-prover commitment
scheme that is secure under the sole assumption that no communication takes
place; no such scheme is known.
In this work, we give strong evidence for a negative answer: we show that any
single-round two-prover commitment scheme can be broken by a non-signaling
attack. Our negative result is as bad as it can get: for any candidate scheme
that is (almost) perfectly hiding, there exists a strategy that allows the
dishonest provers to open a commitment to an arbitrary bit (almost) as
successfully as the honest provers can open an honestly prepared commitment,
i.e., with probability (almost) 1 in case of a perfectly sound scheme. In the
case of multi-round schemes, our impossibility result is restricted to
perfectly hiding schemes.
On the positive side, we show that the impossibility result can be
circumvented by considering three provers instead: there exists a three-prover
commitment scheme that is secure against arbitrary non-signaling attacks
Entanglement swapping using continuous variables
We investigate the efficacy with which entanglement can be teleported using a
continuous measurement scheme. We show that by using the correct gain for the
classical channel the degree of violation of locality that can be demonstrated
(using a CH type inequality) is {\it not} a function of the level of
entanglement squeezing used in the teleportation. This is possible because a
gain condition can always be choosen such that passage through the teleporter
is equivalent to pure attenuation of the input field.Comment: 8 pages, 4 figure
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