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

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