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Alcock J.,University of New Mexico | Maley C.C.,Center for Evolution and Cancer | Maley C.C.,University of California at San Francisco | Maley C.C.,Institute for Advanced Study Berlin | And 4 more authors.
BioEssays | Year: 2014

Microbes in the gastrointestinal tract are under selective pressure to manipulate host eating behavior to increase their fitness, sometimes at the expense of host fitness. Microbes may do this through two potential strategies: (i) generating cravings for foods that they specialize on or foods that suppress their competitors, or (ii) inducing dysphoria until we eat foods that enhance their fitness. We review several potential mechanisms for microbial control over eating behavior including microbial influence on reward and satiety pathways, production of toxins that alter mood, changes to receptors including taste receptors, and hijacking of the vagus nerve, the neural axis between the gut and the brain. We also review the evidence for alternative explanations for cravings and unhealthy eating behavior. Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating. © 2014 The Authors.

Trotzky S.,Ludwig Maximilians University of Munich | Trotzky S.,Max Planck Institute of Quantum Optics | Trotzky S.,Johannes Gutenberg University Mainz | Chen Y.-A.,Ludwig Maximilians University of Munich | And 12 more authors.
Nature Physics | Year: 2012

The problem of how complex quantum systems eventually come to rest lies at the heart of statistical mechanics. The maximum-entropy principle describes which quantum states can be expected in equilibrium, but not how closed quantum many-body systems dynamically equilibrate. Here, we report the experimental observation of the non-equilibrium dynamics of a density wave of ultracold bosonic atoms in an optical lattice in the regime of strong correlations. Using an optical superlattice, we follow its dynamics in terms of quasi-local densities, currents and coherences-all showing a fast relaxation towards equilibrium values. Numerical calculations based on matrix-product states are in an excellent quantitative agreement with the experimental data. The system fulfills the promise of being a dynamical quantum simulator, in that the controlled dynamics runs for longer times than present classical algorithms can keep track of. © 2012 Macmillan Publishers Limited. All rights reserved.

Barthel T.,University of Potsdam | Kliesch M.,University of Potsdam | Eisert J.,University of Potsdam | Eisert J.,Institute for Advanced Study Berlin
Physical Review Letters | Year: 2010

Real-space renormalization approaches for quantum lattice systems generate certain hierarchical classes of states that are subsumed by the multiscale entanglement renormalization Ansatz (MERA). It is shown that, with the exception of one spatial dimension, MERA states are actually states with finite correlations, i.e., projected entangled pair states (PEPS) with a bond dimension independent of the system size. Hence, real-space renormalization generates states which can be encoded with local effective degrees of freedom, and MERA states form an efficiently contractible class of PEPS that obey the area law for the entanglement entropy. It is further pointed out that there exist other efficiently contractible schemes violating the area law. © 2010 The American Physical Society.

Ohliger M.,University of Potsdam | Kieling K.,University of Potsdam | Eisert J.,University of Potsdam | Eisert J.,Institute for Advanced Study Berlin
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We discuss the potential and limitations of Gaussian cluster states for measurement-based quantum computing. Using a framework of Gaussian-projected entangled pair states, we show that no matter what Gaussian local measurements are performed on systems distributed on a general graph, transport and processing of quantum information are not possible beyond a certain influence region, except for exponentially suppressed corrections. We also demonstrate that even under arbitrary non-Gaussian local measurements, slabs of Gaussian cluster states of a finite width cannot carry logical quantum information, even if sophisticated encodings of qubits in continuous-variable systems are allowed for. This is proven by suitably contracting tensor networks representing infinite-dimensional quantum systems. The result can be seen as sharpening the requirements for quantum error correction and fault tolerance for Gaussian cluster states and points toward the necessity of non-Gaussian resource states for measurement-based quantum computing. The results can equally be viewed as referring to Gaussian quantum repeater networks. © 2010 The American Physical Society.

Gross D.,Leibniz University of Hanover | Eisert J.,University of Potsdam | Eisert J.,Institute for Advanced Study Berlin
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We discuss the notion of quantum computational webs: These are quantum states universal for measurement-based computation, which can be built up from a collection of simple primitives. The primitive elements-reminiscent of building blocks in a construction kit-are (i) one-dimensional states (computational quantum wires) with the power to process one logical qubit and (ii) suitable couplings, which connect the wires to a computationally universal web. All elements are preparable by nearest-neighbor interactions in a single pass, of the kind accessible in a number of physical architectures. We provide a complete classification of qubit wires, a physically well-motivated class of universal resources that can be fully understood. Finally, we sketch possible realizations in superlattices and explore the power of coupling mechanisms based on Ising or exchange interactions. © 2010 The American Physical Society.

Gogolin C.,University of Potsdam | Gogolin C.,University of Würzburg | Gogolin C.,University of Bristol | Muller M.P.,University of Potsdam | And 3 more authors.
Physical Review Letters | Year: 2011

We establish a link between unitary relaxation dynamics after a quench in closed many-body systems and the entanglement in the energy eigenbasis. We find that even if reduced states equilibrate, they can have memory on the initial conditions even in certain models that are far from integrable. We show that in such situations the equilibrium states are still described by a maximum entropy or generalized Gibbs ensemble, regardless of whether a model is integrable or not, thereby contributing to a recent debate. In addition, we discuss individual aspects of the thermalization process, comment on the role of Anderson localization, and collect and compare different notions of integrability. © 2011 American Physical Society.

Mari A.,University of Potsdam | Kieling K.,University of Potsdam | Nielsen B.M.,Niels Bohr Institute | Polzik E.S.,Niels Bohr Institute | And 2 more authors.
Physical Review Letters | Year: 2011

We establish a method of directly measuring and estimating nonclassicality-operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows us to certify nonclassicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the nonclassicality of quantum mechanical modes. This method also provides a practical tool to eventually certify such features in mechanical degrees of freedom in opto-mechanics. The proof of the result is based on Bochner's theorem characterizing classical and quantum characteristic functions and on semidefinite programming. In this joint theoretical- experimental work we present data from experimental optical Fock state preparation. © 2011 The American Physical Society.

Cramer M.,University of Ulm | Cramer M.,Imperial College London | Eisert J.,Imperial College London | Eisert J.,University of Potsdam | Eisert J.,Institute for Advanced Study Berlin
New Journal of Physics | Year: 2010

We prove that quantum many-body systems on a one-dimensional lattice locally relax to Gaussian states under non-equilibrium dynamics generated by a bosonic quadratic Hamiltonian. This is true for a large class of initial states-pure or mixed-which have to satisfy merely weak conditions concerning the decay of correlations. The considered setting is a proven instance of a situation where dynamically evolving closed quantum systems locally appear as if they had truly relaxed, to maximum entropy states for fixed second moments. This furthers the understanding of relaxation in suddenly quenched quantum many-body systems. The proof features a non-commutative central limit theorem for non-i.i.d. random variables, showing convergence to Gaussian characteristic functions, giving rise to trace-norm closeness. We briefly link our findings to the ideas of typicality and concentration of measure. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Kieling K.,University of Potsdam | O'Brien J.L.,University of Bristol | Eisert J.,University of Potsdam | Eisert J.,Institute for Advanced Study Berlin
New Journal of Physics | Year: 2010

As primitives for entanglement generation, controlled phase gates have a central role in quantum computing. Especially in ideas realizing instances of quantum computation in linear optical gate arrays, a closer look can be rewarding. In such architectures, all effective nonlinearities are induced by measurements. Hence the probability of success is a crucial parameter of such quantum gates. In this paper, we discuss this question for controlled phase gates that implement an arbitrary phase with one and two control qubits. Within the class of post-selected gates in dual-rail encoding with vacuum ancillas, we identify the optimal success probabilities. We construct networks that allow for implementation using current experimental capabilities in detail. The methods employed here appear specifically useful with the advent of integrated linear optical circuits, providing stable interferometers on monolithic structures. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Wolf H.,Institute for Advanced Study Berlin | Wolf H.,University of Ulm
Journal of Experimental Biology | Year: 2011

Animals have needed to find their way about almost since a free-living life style evolved. Particularly, if an animal has a home - shelter or nesting site - true navigation becomes necessary to shuttle between this home and areas of other activities, such as feeding. As old as navigation is in the animal kingdom, as diverse are its mechanisms and implementations, depending on an organism's ecology and its endowment with sensors and actuators. The use of landmarks for piloting or the use of trail pheromones for route following have been examined in great detail and in a variety of animal species. The same is true for senses of direction - the compasses for navigation - and the construction of vectors for navigation from compass and distance cues. The measurement of distance itself - odometry - has received much less attention. The present review addresses some recent progress in the understanding of odometers in invertebrates, after outlining general principles of navigation to put odometry in its proper context. Finally, a number of refinements that increase navigation accuracy and safety are addressed. © 2011.

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