Quantum cost for sending entanglement

Establishing quantum entanglement between two distant parties is an essential step of many protocols in quantum information processing. One possibility for providing long-distance entanglement is to create an entangled composite state within a lab and then physically send one subsystem to a distant lab. However, is this the "cheapest" way? Here, we investigate the minimal "cost" that is necessary for establishing a certain amount of entanglement between two distant parties. We prove that this cost is intrinsically quantum, and is specified by quantum correlations. Our results provide an optimal protocol for entanglement distribution and show that quantum correlations are the essential resource for this task.Comment: Added a reference to the related article arXiv:1203.1268 by T. K. Chuan et a

Easy implementable algorithm for the geometric measure of entanglement

We present an easy implementable algorithm for approximating the geometric measure of entanglement from above. The algorithm can be applied to any multipartite mixed state. It involves only the solution of an eigenproblem and finding a singular value decomposition, no further numerical techniques are needed. To provide examples, the algorithm was applied to the isotropic states of 3 qubits and the 3-qubit XX model with external magnetic field.Comment: 9 pages, 3 figure

Efficient design of piezoresitive sensors based on carbon black conductive composites

Flexible and stretchable sensors are widely investigated taking into account their potential for wearable electronics, such as electronic skin, healthcare monitoring, human-machine interfaces, and soft robotics. In this contribution, highly sensitive conductive polymer composites (CPCs) for piezoresistive sensing are summarized, considering a straightforward manufacturing process based on extrusion of thermoplastic polyurethane (TPU) and/or olefin block copolymer (OBC), carbon black (CB), and additionally polyethylene-octene elastomer (POE) grafted with maleic anhydride (POE-g-MA). The design of the formulation variables is successfully performed to enable both low and high strain sensing, as highlighted by both static and dynamic testing

Experimental generation of pseudo bound entanglement

We use Nuclear Magnetic Resonance (NMR) to experimentally generate a bound entangled (more precisely: pseudo bound entangled) state, i.e. a quantum state which is non-distillable but nevertheless entangled. Our quantum system consists of three qubits. We characterize the produced state via state tomography to show that the created state has a positive partial transposition with respect to any bipartite splitting, and we use a witness operator to prove its entanglement.Comment: 5 page

Reversible quantum teleportation in an optical lattice

We propose a protocol, based on entanglement procedures recently suggested by [D. Jaksch et al., Phys. Rev. Lett. 82, 1975 (1999)], which allows the teleportation of an unknown state of a neutral atom in an optical lattice to another atom in another site of the lattice, without any irreversible detection.Comment: 8 pages, 3 figure

Linking a distance measure of entanglement to its convex roof

An important problem in quantum information theory is the quantification of entanglement in multipartite mixed quantum states. In this work, a connection between the geometric measure of entanglement and a distance measure of entanglement is established. We present a new expression for the geometric measure of entanglement in terms of the maximal fidelity with a separable state. A direct application of this result provides a closed expression for the Bures measure of entanglement of two qubits. We also prove that the number of elements in an optimal decomposition w.r.t. the geometric measure of entanglement is bounded from above by the Caratheodory bound, and we find necessary conditions for the structure of an optimal decomposition.Comment: 11 pages, 4 figure

A field deployable method for a rapid screening analysis of inorganic arsenic in seaweed

The authors thank the support for getting the seaweed samples from the projects funded under the Department of Agriculture, Food and the Marine’s Competitive research programmes in Ireland. Reference number 14 SF 860. The authors thank Corny Brombach for the graphical abstract.Peer reviewedPublisher PD

Effect of magnesium therapy on nocturnal leg cramps: a systematic review of randomized controlled trials with meta-analysis using simulations

Background and objective. Nocturnal leg cramps (NLC) are common in primary care and may cause severe pain and sleep disturbance. We systematically reviewed the effectiveness of magnesium in treating NLC and the side-effect profile of magnesium compared to placebo. Methods. We searched Medline, Embase, Cochrane Library, ClinicalTrials.gov, the International Standard Randomised Controlled Trial Number and the International Clinical Trials Registry Platform registries until August 2012. All randomized controlled trials (RCTs) comparing magnesium therapy for NLC in adults with any other comparator were eligible. Two investigators independently selected, extracted data from and rated the risk of bias of relevant studies. To compensate for the heterogeneity in outcome measures, simulations were used to summarize the data. Results. Seven RCTs were included in the review (n = 361), all comparing magnesium to placebo. Three of these trials included only pregnant women. The difference in the median number of leg cramps per week between the placebo and the intervention groups was 0.345 (quantile 2.5%: −0.133, quantile 97.5%: 0.875). This difference was 0.807 (quantile 2.5%: 0.015, quantile 97.5%: 1.207) in the three studies involving only pregnant women and 0.362 (quantile 2.5%: −0.386, quantile 97.5%: 1.148) in the others. Overall gastrointestinal side effects were slightly more common with magnesium therapy than with placebo. The strength of this evidence was weak, mainly due to small study sizes and short follow-up. Conclusions. Magnesium therapy does not appear to be effective in the treatment of NLC in the general population, but may have a small effect in pregnant women. Further research using better designed RCTs is necessar

Finite key analysis for symmetric attacks in quantum key distribution

We introduce a constructive method to calculate the achievable secret key rate for a generic class of quantum key distribution protocols, when only a finite number n of signals is given. Our approach is applicable to all scenarios in which the quantum state shared by Alice and Bob is known. In particular, we consider the six state protocol with symmetric eavesdropping attacks, and show that for a small number of signals, i.e. below the order of 10^4, the finite key rate differs significantly from the asymptotic value for n approaching infinity. However, for larger n, a good approximation of the asymptotic value is found. We also study secret key rates for protocols using higher-dimensional quantum systems.Comment: 9 pages, 5 figure