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TABLE OF CONTENTS April 2014 Volume 10, Issue 4 Insight Editorials Thesis Research Highlights News and Views Commentaries Progress Article Reviews Letters Articles Futures Subscribe   Facebook   RSS   Recommend to library   Twitter   Advertisement Nature Physics Insight: Foundations of quantum mechanics  Published in April 2014 this Insight explores recent trends in the study of the foundations of quantum mechanics: from expanding or even rethinking quantum theory, to ambitious new experiments that will seek the elusive effects of quantum gravity.    Insight Top Insight on Foundations of Quantum Mechanics Table of contents Over the past two decades, the fields of quantum information theory and quantum technology have emerged and matured. The theoretical and experimental tools developed in this context are now making it possible to revisit the very foundations of quantum theory, and to explore the terra incognita that may lie beyond. In this Insight, we survey recent trends in the study of the foundations of quantum mechanics: from the expansion or even rethinking of quantum theory, to ambitious new experiments that will seek the elusive effects of quantum gravity. Editorials Top Strength in numbers   p241 doi:10.1038/nphys2953 A spectacular result for inflationary cosmology needs independent confirmation. Thesis Top Great leap outwards   p243 Mark Buchanan doi:10.1038/nphys2943 Research Highlights Top Razzle dazzle 'em | Two by two | Electrons of a different stripe | Know your onions | No coincidence News and Views Top Microwave photonics: Optomechanics sets the beat   pp245 - 246 Mankei Tsang doi:10.1038/nphys2923 A tiny drum converts between infrared and microwave signals with record efficiency by keeping the beat of both. See also: Article by Andrews et al. Quasicrystals: Making ends meet   p246 Bart Verberck doi:10.1038/nphys2944 Topological insulators: Strain away   pp247 - 248 Jinfeng Jia doi:10.1038/nphys2936 Surface states are the salient feature of topological insulators. Now, experiments demonstrate that surface states can be enhanced or destroyed by applying compressive or tensile strain. See also: Letter by Liu et al. Bell's theorem: Closing the loopholes   p248 Iulia Georgescu doi:10.1038/nphys2945 Organic spintronics: Pumping spins through polymers   pp249 - 250 Bert Koopmans doi:10.1038/nphys2928 Spin pumping and spin-to-charge conversion in hybrid metal-organic devices reveal the physical mechanisms at work in semiconducting polymers. See also: Article by Watanabe et al. Physics JOBS of the week Tenure-Track Position in Materials Chemistry and Physics Université du Québec à Trois-Rivières (UQTR) PhD Position for Computer Simulations in Soft Matter Physics Forschungszentrum Jülich - Helmholtz Association PhD Studentship in Physics of Aerospace Metals The University of Manchester Senior Lecturer / Lecturer in Physics Stellenbosch University (South Africa) Post-doctoral Research Associate in Biomedical Optics and Physics University of North Carolina at Chapel Hill More Science jobs from Physics EVENT 2nd Frontiers in Computational Physics: Energy Sciences 8th Sept 2014 ETH Zurich, Switzerland More science events from Editorial Top Insight on Foundations of Quantum Mechanics Foundations of quantum mechanics   p253 Iulia Georgescu doi:10.1038/nphys2934 Commentaries Top Insight on Foundations of Quantum Mechanics Gravity in quantum mechanics   pp254 - 255 Giovanni Amelino-Camelia doi:10.1038/nphys2876 Gravity and quantum mechanics tend to stay out of each other's way, but this might change as we devise new experiments to test the applicability of quantum theory to macroscopic systems and larger length scales. Insight on Foundations of Quantum Mechanics Quantum entanglement   pp256 - 258 Vlatko Vedral doi:10.1038/nphys2904 Recent advances in quantum information theory reveal the deep connections between entanglement and thermodynamics, many-body theory, quantum computing and its link to macroscopicity. Progress Article Top Insight on Foundations of Quantum Mechanics Quantum causality   pp259 - 263 Časlav Brukner doi:10.1038/nphys2930 Revisiting the notion of causality in quantum mechanics may lead to new directions in quantum information theory and quantum gravity research. Reviews Top Insight on Foundations of Quantum Mechanics Nonlocality beyond quantum mechanics   pp264 - 270 Sandu Popescu doi:10.1038/nphys2916 There are good reasons to consider nonlocality to be the defining feature of quantum mechanics, but stronger nonlocal correlations than those predicted by quantum theory could exist, which raises the intriguing question of what lies beyond. Insight on Foundations of Quantum Mechanics Testing the limits of quantum mechanical superpositions   pp271 - 277 Markus Arndt and Klaus Hornberger doi:10.1038/nphys2863 Testing the limits of the quantum mechanical description of nature has become a subject of intense experimental interest. Recent advances in investigating macroscopic quantum superpositions are pushing these limits. Insight on Foundations of Quantum Mechanics Testing foundations of quantum mechanics with photons   pp278 - 286 Peter Shadbolt, Jonathan C. F. Mathews, Anthony Laing and Jeremy L. O'Brien doi:10.1038/nphys2931 Starting with wave-particle duality, experiments with light have played a major role in the development of quantum theory. Advances in photonic technologies allow for improved tests of quantum complementarity, delayed-choice and nonlocality. Letters Top Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice   pp289 - 293 Matthias Punk, Debanjan Chowdhury and Subir Sachdev doi:10.1038/nphys2887 A quantum spin liquid is a spin state with no magnetic order even at the lowest temperatures. To explain neutron scattering data on a 'kagome lattice' antiferromagnet, visons (elementary excitations of vortices) must be included, in addition to the usual fractionalized spinons. Tuning Dirac states by strain in the topological insulator Bi2Se3   pp294 - 299 Y. Liu, Y. Y. Li, S. Rajput, D. Gilks, L. Lari et al. doi:10.1038/nphys2898 Bismuth selenide is a prototypical 3D topological insulator; its electronic spectrum features a Dirac cone populated by surface states. Now, it is experimentally and numerically shown that a bandgap forms beyond a certain critical compressive strain, destroying the surface states. See also: News and Views by Jia Bipartite magnetic parent phases in the iron oxypnictide superconductor   pp300 - 303 M. Hiraishi, S. Iimura, K. M. Kojima, J. Yamaura, H. Hiraka et al. doi:10.1038/nphys2906 Superconductivity in iron pnictide compounds occurs near a magnetic phase and magnetic spin fluctuations are prime candidates for the superconducting pairing mechanism. What does this mean now that a second magnetic phase, next to another superconducting phase, is found at higher doping levels? Origins of bad-metal conductivity and the insulator-metal transition in the rare-earth nickelates   pp304 - 307 R. Jaramillo, Sieu D. Ha, D. M. Silevitch and Shriram Ramanathan doi:10.1038/nphys2907 Bad metals, such as the copper oxide superconductors, do conduct electricity but the origin of their poor conductivity is unclear. A study of disordered rare-earth nickelates now provides microscopic insights into bad-metal behaviour Articles Top Polaron spin current transport in organic semiconductors   pp308 - 313 Shun Watanabe, Kazuya Ando, Keehoon Kang, Sebastian Mooser, Yana Vaynzof et al. doi:10.1038/nphys2901 The transport and relaxation mechanisms in organic semiconductors are still insufficiently understood, but measurements now show that in these materials polarons carry pure spin currents over extended distances with long relaxation times, and uncover the role of spin-orbit coupling in this process. See also: News and Views by Koopmans Experimental determination of the finite-temperature phase diagram of a spin-orbit coupled Bose gas   pp314 - 320 Si-Cong Ji, Jin-Yi Zhang, Long Zhang, Zhi-Dong Du, Wei Zheng et al. doi:10.1038/nphys2905 Spin-orbit coupling in Bose gases is expected to lead to new phenomena, but the thermodynamic properties are not yet fully understood. An ultracold atom experiment using artificial spin-orbit coupling uncovers the finite-temperature phase diagram and a transition between a stripe-ordered and a magnetized phase. Bidirectional and efficient conversion between microwave and optical light   pp321 - 326 R. W. Andrews, R. W. Peterson, T. P. Purdy, K. Cicak, R. W. Simmonds et al. doi:10.1038/nphys2911 An optomechanical system that converts microwaves to optical frequency light and vice versa is demonstrated. The technique achieves a conversion efficiency of approximately 10%. The results indicate that the device could work at the quantum level, up- and down-converting individual photons, if it were cooled to millikelvin temperatures. It could, therefore, form an integral part of quantum-processor networks. See also: News and Views by Tsang Futures Top The stuff we don't do   p328 Marissa Lingen doi:10.1038/nphys2952 It's time for a life lesson. 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