Nature Physics 5, 775 (2009). doi:10.1038/nphys1440

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Nature Physics 5, 780 (2009). doi:10.1038/nphys1454

Author: Ed Gerstner

The 2009 Nobel Prize in Physics has been awarded to Charles K. Kao for the development of optical fibres for telecommunications, and to Willard S. Boyle and George E. Smith for the invention of charge-coupled device sensors.

Nature Physics 5, 781 (2009). doi:10.1038/nphys1435

Author: Helmut Ritsch

Cold atoms and photons confined together in high-quality optical resonators self-organize into complicated crystalline structures that have an optical-wavelength scale. Complex solid-state phenomena can be studied in real time on directly observable scales.

Nature Physics 5, 783 (2009). doi:10.1038/nphys1434

Author: Friedrich C. Simmel

Coating nanowires with lipid bilayers allows the use of biological ion channels as biosensors.

Nature Physics 5, 784 (2009). doi:10.1038/nphys1439

Author: Kareljan Schoutens

Proliferation of so-called anyonic defects in a topological phase of quantum matter leads to a critical state that can be visualized as a 'quantum foam', with topology-changing fluctuations on all length scales.

Nature Physics 5, 786 (2009). doi:10.1038/nphys1448

Author: R. Paul Drake

One way to collect data about black holes is to analyse the X-rays emitted from the surrounding plasmas heated to extreme temperatures by the flux of photons flowing into them. The use of intense lasers to recreate these conditions in the lab provides a potentially valuable tool for understanding what these data mean.

Nature Physics 5, 787 (2009). doi:10.1038/nphys1449

Author: C. W. Chu

The discovery of iron-based pnictide superconductors may have reinvigorated the field of high-temperature superconductivity, but the cuprate superconductors are still in the game.

Nature Physics 5, 791 (2009). doi:10.1038/nphys1400

Authors: François Mallet, Florian R. Ong, Agustin Palacios-Laloy, François Nguyen, Patrice Bertet, Denis Vion & Daniel Esteve

The future development of quantum information using superconducting circuits requires Josephson qubits with long coherence times combined with a high-fidelity readout. Significant progress in the control of coherence has recently been achieved using circuit quantum electrodynamics architectures, where the qubit is embedded in a coplanar waveguide resonator, which both provides a well-controlled electromagnetic environment and serves as qubit readout. In particular, a new qubit design, the so-called transmon, yields reproducibly long coherence times. However, a high-fidelity single-shot readout of the transmon, desirable for running simple quantum algorithms or measuring quantum correlations in multi-qubit experiments, is still lacking. Here, we demonstrate a new transmon circuit where the waveguide resonator is turned into a sample-and-hold detector—more specifically, a Josephson bifurcation amplifier—which allows both fast measurement and single-shot discrimination of the qubit states. We report Rabi oscillations with a high visibility of 94%, together with dephasing and relaxation times longer than 0.5 μs. By carrying out two measurements in series, we also demonstrate that this new readout does not induce extra qubit relaxation.

Nature Physics 5, 796 (2009). doi:10.1038/nphys1392

Authors: Kristjan Haule & Gabriel Kotliar

Complex electronic matter shows subtle forms of self-organization, which are almost invisible to the available experimental tools. One prominent example is provided by the heavy-fermion material URu2Si2. At high temperature, the 5f electrons of uranium carry a very large entropy. This entropy is released at 17.5 K by means of a second-order phase transition to a state that remains shrouded in mystery, termed a ‘hidden order’ state. Here, we develop a first-principles theoretical method to analyse the electronic spectrum of correlated materials as a function of the position inside the unit cell of the crystal and use it to identify the low-energy excitations of URu2Si2. We identify the order parameter of the hidden-order state and show that it is intimately connected to magnetism. Below 70 K, the 5f electrons undergo a multichannel Kondo effect, which is ‘arrested’ at low temperature by the crystal-field splitting. At lower temperatures, two broken-symmetry states emerge, characterized by a complex order parameter ψ. A real ψ describes the hidden-order phase and an imaginary ψ corresponds to the large-moment antiferromagnetic phase. Together, they provide a unified picture of the two broken-symmetry phases in this material.

Nature Physics 5, 800 (2009). doi:10.1038/nphys1397

Authors: Jinho Lee, M. P. Allan, M. A. Wang, J. Farrell, S. A. Grigera, F. Baumberger, J. C. Davis & A. P. Mackenzie

The intriguing idea that strongly interacting electrons can generate spatially inhomogeneous electronic liquid-crystalline phases is over a decade old, but these systems still represent an unexplored frontier of condensed-matter physics. One reason is that visualization of the many-body quantum states generated by the strong interactions, and of the resulting electronic phases, has not been achieved. Soft condensed-matter physics was transformed by microscopies that enabled imaging of real-space structures and patterns. A candidate technique for obtaining equivalent data in the purely electronic systems is spectroscopic imaging scanning tunnelling microscopy (SI-STM). The core challenge is to detect the tenuous but ‘heavy’ momentum (k)-space components of the many-body electronic state simultaneously with its real-space constituents. Sr3Ru2O7 provides a particularly exciting opportunity to address these issues. It possesses a very strongly renormalized ‘heavy’ d-electron Fermi liquid and exhibits a field-induced transition to an electronic liquid-crystalline phase. Finally, as a layered compound, it can be cleaved to present an excellent surface for SI-STM.

Nature Physics 5, 805 (2009). doi:10.1038/nphys1364

Authors: Alberto Amo, Jérôme Lefrère, Simon Pigeon, Claire Adrados, Cristiano Ciuti, Iacopo Carusotto, Romuald Houdré, Elisabeth Giacobino & Alberto Bramati

Superfluidity, the ability of a quantum fluid to flow without friction, is one of the most spectacular phenomena occurring in degenerate gases of interacting bosons. Since its first discovery in liquid helium-4 (refs 1, 2), superfluidity has been observed in quite different systems, and recent experiments with ultracold trapped atoms have explored the subtle links between superfluidity and Bose–Einstein condensation. In solid-state systems, it has been anticipated that exciton–polaritons in semiconductor microcavities should behave as an unusual quantum fluid, with unique properties stemming from its intrinsically non-equilibrium nature. This has stimulated the quest for an experimental demonstration of superfluidity effects in polariton systems. Here, we report clear evidence for superfluid motion of polaritons. Superfluidity is investigated in terms of the Landau criterion and manifests itself as the suppression of scattering from defects when the flow velocity is slower than the speed of sound in the fluid. Moreover, a Čerenkov-like wake pattern is observed when the flow velocity exceeds the speed of sound. The experimental findings are in quantitative agreement with predictions based on a generalized Gross–Pitaevskii theory, and establish microcavity polaritons as a system for exploring the rich physics of non-equilibrium quantum fluids.

Nature Physics 5, 811 (2009). doi:10.1038/nphys1393

Authors: J. J. H. Pijpers, R. Ulbricht, K. J. Tielrooij, A. Osherov, Y. Golan, C. Delerue, G. Allan & M. Bonn

One of the important factors limiting solar-cell efficiency is that incident photons generate one electron–hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells. Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions. Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carrier-multiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.

Nature Physics 5, 815 (2009). doi:10.1038/nphys1398

Authors: Dylan C. Yost, Thomas R. Schibli, Jun Ye, Jennifer L. Tate, James Hostetter, Mette B. Gaarde & Kenneth J. Schafer

Recent demonstrations of high-harmonic generation (HHG) at very high repetition frequencies (∼100 MHz) may allow for the revolutionary transfer of frequency combs to the vacuum-ultraviolet range. This advance necessitates unifying optical frequency-comb technology with strong-field atomic physics. Whereas strong-field studies of HHG have often focused on above-threshold harmonic generation (photon energy above the ionization potential), for vacuum-ultraviolet frequency combs an understanding of below-threshold harmonic orders and their generation process is crucial. Here, we present a new and quantitative study of the harmonics 7–13 generated below and near the ionization threshold in xenon gas with an intense 1,070 nm driving field. We show multiple generation pathways for these harmonics that are manifested as on-axis interference in the harmonic yield. This discovery provides a new understanding of the strong-field, below-threshold dynamics under the influence of an atomic potential and allows us to quantitatively assess the achievable coherence of a vacuum-ultraviolet frequency comb generated through below-threshold harmonics. We find that under reasonable experimental conditions, temporal coherence is maintained. As evidence, we present the first explicit vacuum-ultraviolet frequency-comb structure beyond the third harmonic.

Nature Physics 5, 821 (2009). doi:10.1038/nphys1402

Authors: Shinsuke Fujioka, Hideaki Takabe, Norimasa Yamamoto, David Salzmann, Feilu Wang, Hiroaki Nishimura, Yutong Li, Quanli Dong, Shoujun Wang, Yi Zhang, Yong-Joo Rhee, Yong-Woo Lee, Jae-Min Han, Minoru Tanabe, Takashi Fujiwara, Yuto Nakabayashi, Gang Zhao, Jie Zhang & Kunioki Mima

X-ray spectroscopy is an important tool for understanding the extreme photoionization processes that drive the behaviour of non-thermal equilibrium plasmas in compact astrophysical objects such as black holes. Even so, the distance of these objects from the Earth and the inability to control or accurately ascertain the conditions that govern their behaviour makes it difficult to interpret the origin of the features in astronomical X-ray measurements. Here, we describe an experiment that uses the implosion driven by a 3 TW, 4 kJ laser system to produce a 0.5 keV blackbody radiator that mimics the conditions that exist in the neighbourhood of a black hole. The X-ray spectra emitted from photoionized silicon plasmas resemble those observed from the binary stars Cygnus X-3 (refs 7, 8) and Vela X-1 (refs 9, 1011) with the Chandra X-ray satellite. As well as demonstrating the ability to create extreme radiation fields in a laboratory plasma, our theoretical interpretation of these laboratory spectra contrasts starkly with the generally accepted explanation for the origin of similar features in astronomical observations. Our experimental approach offers a powerful means to test and validate the computer codes used in X-ray astronomy.

Nature Physics 5, 826 (2009). doi:10.1038/nphys1404

Authors: Matthias Fuchs, Raphael Weingartner, Antonia Popp, Zsuzsanna Major, Stefan Becker, Jens Osterhoff, Isabella Cortrie, Benno Zeitler, Rainer Hörlein, George D. Tsakiris, Ulrich Schramm, Tom P. Rowlands-Rees, Simon M. Hooker, Dietrich Habs, Ferenc Krausz, Stefan Karsch & Florian Grüner

Synchrotrons and free-electron lasers are the most powerful sources of X-ray radiation. They constitute invaluable tools for a broad range of research; however, their dependence on large-scale radiofrequency electron accelerators means that only a few of these sources exist worldwide. Laser-driven plasma-wave accelerators provide markedly increased accelerating fields and hence offer the potential to shrink the size and cost of these X-ray sources to the university-laboratory scale. Here, we demonstrate the generation of soft-X-ray undulator radiation with laser-plasma-accelerated electron beams. The well-collimated beams deliver soft-X-ray pulses with an expected pulse duration of ∼10 fs (inferred from plasma-accelerator physics). Our source draws on a 30-cm-long undulator and a 1.5-cm-long accelerator delivering stable electron beams with energies of ∼210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centred at a wavelength of ∼18 nm (fundamental), a second peak near ∼9 nm (second harmonic) and a high-energy cutoff at ∼7 nm. Magnetic quadrupole lenses ensure efficient electron-beam transport and demonstrate an enabling technology for reproducible generation of tunable undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of tunable, brilliant, ultrashort-pulsed X-ray sources for small-scale laboratories.

Nature Physics 5, 830 (2009). doi:10.1038/nphys1389

Authors: Erez Berg, Eduardo Fradkin & Steven A. Kivelson

Nature Physics 5, 834 (2009). doi:10.1038/nphys1396

Authors: Charlotte Gils, Simon Trebst, Alexei Kitaev, Andreas W. W. Ludwig, Matthias Troyer & Zhenghan Wang

Nature Physics 5, 840 (2009). doi:10.1038/nphys1399

Authors: J. Červenka, M. I. Katsnelson & C. F. J. Flipse

Nature Physics 5, 845 (2009). doi:10.1038/nphys1403

Authors: Sarang Gopalakrishnan, Benjamin L. Lev & Paul M. Goldbart