Device-Independent Detection of Genuine Multipartite Entanglement for All Pure States.

We show that genuine multipartite entanglement of all multipartite pure states in arbitrary finite dimension can be detected in a device-independent way by employing bipartite Bell inequalities on states that are deterministically generated from the initial state via local operations. This leads to an efficient scheme for large classes of multipartite states that are relevant in quantum computation or condensed-matter physics, including cluster states and the ground state of the Affleck-Kennedy-Lieb-Tasaki (AKLT) model. For cluster states the detection of genuine multipartite entanglement involves only measurements on a constant number of systems with an overhead that scales linearly with the system size, while for the AKLT model the overhead is polynomial. In all cases our approach shows some robustness against experimental imperfections.

Multipartite state generation in quantum networks with optimal scaling.

We introduce a repeater scheme to efficiently distribute multipartite entangled states in a quantum network with optimal scaling. The scheme allows to generate graph states such as 2D and 3D cluster states of growing size or GHZ states over arbitrary distances, with a constant overhead per node/channel that is independent of the distance. The approach is genuine multipartite, and is based on the measurement-based implementation of multipartite hashing, an entanglement purification protocol that operates on a large ensemble together with local merging/connection of elementary building blocks. We analyze the performance of the scheme in a setting where local or global storage is limited, and compare it to bipartite and hybrid approaches that are based on the distribution of entangled pairs. We find that the multipartite approach offers a storage advantage, which results in higher efficiency and better performance in certain parameter regimes. We generalize our approach to arbitrary network topologies and different target graph states.

Long-Range Big Quantum-Data Transmission.

We introduce an alternative type of quantum repeater for long-range quantum communication with improved scaling with the distance. We show that by employing hashing, a deterministic entanglement distillation protocol with one-way communication, one obtains a scalable scheme that allows one to reach arbitrary distances, with constant overhead in resources per repeater station, and ultrahigh rates. In practical terms, we show that, also with moderate resources of a few hundred qubits at each repeater station, one can reach intercontinental distances. At the same time, a measurement-based implementation allows one to tolerate high loss but also operational and memory errors of the order of several percent per qubit. This opens the way for long-distance communication of big quantum data.

Hybrid architecture for encoded measurement-based quantum computation.

We present a hybrid scheme for quantum computation that combines the modular structure of elementary building blocks used in the circuit model with the advantages of a measurement-based approach to quantum computation. We show how to construct optimal resource states of minimal size to implement elementary building blocks for encoded quantum computation in a measurement-based way, including states for error correction and encoded gates. The performance of the scheme is determined by the quality of the resource states, where within the considered error model a threshold of the order of 10% local noise per particle for fault-tolerant quantum computation and quantum communication.

Experimental violation of multipartite Bell inequalities with trapped ions.

We report on the experimental violation of multipartite Bell inequalities by entangled states of trapped ions. First, we consider resource states for measurement-based quantum computation of between 3 and 7 ions and show that all strongly violate a Bell-type inequality for graph states, where the criterion for violation is a sufficiently high fidelity. Second, we analyze Greenberger-Horne-Zeilinger states of up to 14 ions generated in a previous experiment using stronger Mermin-Klyshko inequalities, and show that in this case the violation of local realism increases exponentially with system size. These experiments represent a violation of multipartite Bell-type inequalities of deterministically prepared entangled states. In addition, the detection loophole is closed.

Measurement-based quantum computation with trapped ions.

Measurement-based quantum computation represents a powerful and flexible framework for quantum information processing, based on the notion of entangled quantum states as computational resources. The most prominent application is the one-way quantum computer, with the cluster state as its universal resource. Here we demonstrate the principles of measurement-based quantum computation using deterministically generated cluster states, in a system of trapped calcium ions. First we implement a universal set of operations for quantum computing. Second we demonstrate a family of measurement-based quantum error correction codes and show their improved performance as the code length is increased. The methods presented can be directly scaled up to generate graph states of several tens of qubits.

Universal and optimal error thresholds for measurement-based entanglement purification.

We investigate measurement-based entanglement purification protocols (EPP) in the presence of local noise and imperfections. We derive a universal, protocol-independent threshold for the required quality of the local resource states, where we show that local noise per particle of up to 24% is tolerable. This corresponds to an increase of the noise threshold by almost an order of magnitude, based on the joint measurement-based implementation of sequential rounds of few-particle EPP. We generalize our results to multipartite EPP, where we encounter similarly high error thresholds.

Efectos de dos técnicas manuales aplicadas en la región lumbar en el patrón de activación del erector espinal / Effects of two different manual techniques in the lumbar region on the erector spinae activation pattern

Objetivo Estudiar el comportamiento del músculo erector espinal durante la flexo-extensión de tronco, tras la aplicación de una técnica de inducción miofascial y una técnica manipulativa. Hipótesis Tras la aplicación de dichas técnicas podría producirse una disminución en la intensidad de la actividad electromiográfica (EMG) del erector espinal. Material y métodos En 32 sujetos voluntarios sanos se registró bilateralmente la actividad EMG de superficie del erector espinal, durante la realización de cinco flexo-extensiones de tronco, antes y después de cada una de las técnicas. Las variables del estudio fueron la actividad EMG media durante el silencio mioeléctrico, así como la EMG máxima y media del erector espinal durante sus contracciones concéntrica y excéntrica. Resultados Tras la aplicación de la técnica miofascial y manipulativa, se observó una disminución significativa en todas las variables estudiadas excepto en la EMG máxima durante las fases concéntrica y excéntrica. Conclusión Tras una intervención combinada de inducción miofascial de la fascia toracolumbar y manipulación vertebral a nivel de L3, se produce una disminución en la actividad EMG del erector espinal, lo que podría deberse a una inhibición de dicha musculatura (AU)

Objective To study erector spinae behavior during trunk flexion and extension, following the application of a myofascial induction technique and a spinal manipulation. Hypotheses The application of these techniques could cause a decrease in the electromyographic activity (EMG) of the erector spinae. Material and methods The EMG activity of the erector spinae surface during five trunk flexion and extension, before and after each one of the techniques was recorded in 32 healthy volunteer subjects. The study variables were mean EMG activity during myoelectrical silence and the maximum and median EMG of the erector spinae during its concentric and eccentric phases. Results A significant reduction in all the variables studied except maximum EMG during the concentric and eccentric phases was observed following the application of the myofascial technique and spinal manipulation. Conclusion After a combined intervention of a myofascial induction technique of the thoracolumbar fascia and a spinal manipulation at L3 level, a decrease in the EMG activity of erector spinae is found. This could be due to an inhibition of the erector spinae muscle (AU)