The rise of big data represents an opportunity for physicists. To take full advantage, however, they need a subtle but important shift in mindset.

]]>Author: Jeff Byers

Physicists are accustomed to dealing with large datasets, yet they are fortunate in that the quality of their experimental data is very good. The onset of big data has led to an explosion of datasets with a far more complex structure — a development that requires new tools and a different mindset.

]]>Author: Mark Buchanan

]]>Author: Federico Levi

]]>Author: Andreas Trabesinger

]]>Author: Iulia Georgescu

]]>Author: Federico Levi

]]>Author: Yun Li

]]>Author: Luke Fleet

]]>Author: Raffaele Flaminio

The Einstein–Podolsky–Rosen type of quantum entanglement can be used to improve the sensitivity of laser interferometer gravitational-wave detectors beyond the quantum limit.

]]>Author: Monika Schleier-Smith

Quantum information encoded in one of many interacting particles quickly becomes scrambled. A set of tools for tracking this process is on its way.

]]>Author: Koji Muraki

An excitonic Bose–Einstein condensate has so far been realized only in particular semiconductor heterostructure setups. Now, experiments show that such condensates can form in double graphene bilayers separated by hexagonal boron nitride.

]]>Author: Klaus Kroy

Standard rheology tells us how a cell responds to deformation. But ramping up the frequency reveals more about its internal dynamics and morphology, mapping a route to improved drug treatments — and possible insight into the malignancy of cancers.

]]>Authors: Jacob Johansen, B. J. DeSalvo, Krutik Patel & Cheng Chin

Efimov physics is a universal phenomenon in quantum three-body systems. For systems with resonant two-body interactions, Efimov predicted an infinite series of three-body bound states with geometric scaling symmetry. These Efimov states, first observed in cold caesium atoms, have been recently reported in a variety of other atomic systems. The intriguing prospect of a universal absolute Efimov resonance position across Feshbach resonances remains an open question. Theories predict a strong dependence on the resonance strength for closed-channel-dominated Feshbach resonances, whereas experimental results have so far been consistent with the universal prediction. Here we directly compare the Efimov spectra in a 6Li–133Cs mixture near two Feshbach resonances which are very different in their resonance strengths, but otherwise almost identical. Our result shows a clear dependence of the absolute Efimov resonance position on Feshbach resonance strength and a clear departure from the universal prediction for the narrow Feshbach resonance.

]]>Authors: P. A. McClarty, F. Krüger, T. Guidi, S. F. Parker, K. Refson, A. W. Parker, D. Prabhakaran & R. Coldea

The twin discoveries of the quantum Hall effect, in the 1980s, and of topological band insulators, in the 2000s, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has initiated a hunt for topological insulators in bosonic systems: in photonic crystals, in the vibrational modes of crystals, and in the excitations of ordered magnets. Using inelastic neutron scattering along with theoretical calculations, we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu2(BO3)2 is a bosonic topological insulator with topologically protected chiral edge modes of triplon excitations.

]]>Authors: K. Grube, S. Zaum, O. Stockert, Q. Si & H. v. Löhneysen

The third law of thermodynamics states that the entropy of any system in equilibrium has to vanish at absolute zero temperature. At nonzero temperatures, on the other hand, matter is expected to accumulate entropy near a quantum critical point, where it undergoes a continuous transition from one ground state to another. Here, we determine, based on general thermodynamic principles, the spatial-dimensional profile of the entropy S near a quantum critical point and its steepest descent in the corresponding multidimensional stress space. We demonstrate this approach for the canonical quantum critical compound CeCu 6−xAux near its onset of antiferromagnetic order. We are able to link the directional stress dependence of S to the previously determined geometry of quantum critical fluctuations. Our demonstration of the multidimensional entropy landscape provides the foundation to understand how quantum criticality nucleates novel phases such as high-temperature superconductivity.

]]>Authors: Xiaomeng Liu, Kenji Watanabe, Takashi Taniguchi, Bertrand I. Halperin & Philip Kim

An exciton condensate is a Bose–Einstein condensate of electron and hole pairs bound by the Coulomb interaction. In an electronic double layer (EDL) subject to strong magnetic fields, filled Landau states in one layer bind with empty states of the other layer to form an exciton condensate. Here we report exciton condensation in a bilayer graphene EDL separated by hexagonal boron nitride. Driving current in one graphene layer generates a near-quantized Hall voltage in the other layer, resulting in coherent exciton transport. Owing to the strong Coulomb coupling across the atomically thin dielectric, quantum Hall drag in graphene appears at a temperature ten times higher than previously observed in a GaAs EDL. The wide-range tunability of densities and displacement fields enables exploration of a rich phase diagram of Bose–Einstein condensates across Landau levels with different filling factors and internal quantum degrees of freedom. The observed robust exciton condensation opens up opportunities to investigate various many-body exciton phases.

]]>Authors: J. I. A. Li, T. Taniguchi, K. Watanabe, J. Hone & C. R. Dean

A spatially indirect exciton is created when an electron and a hole, confined to separate layers of a double quantum well system, bind to form a composite boson. Such excitons are long-lived, and in the limit of strong interactions are predicted to undergo a Bose–Einstein condensate-like phase transition into a superfluid ground state. Here, we report evidence of an exciton condensate in the quantum Hall effect regime of double-layer structures of bilayer graphene. Interlayer correlation is identified by quantized Hall drag at matched layer densities, and the dissipationless nature of the phase is confirmed in the counterflow geometry. A selection rule for the condensate phase is observed involving both the orbital and valley indices of bilayer graphene. Our results establish double bilayer graphene as an ideal system for studying the rich phase diagram of strongly interacting bosonic particles in the solid state.

]]>Authors: Landry Bretheau, Joel I-Jan Wang, Riccardo Pisoni, Kenji Watanabe, Takashi Taniguchi & Pablo Jarillo-Herrero

A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties. This proximity effect microscopically originates from the formation in the conductor of entangled electron–hole states, called Andreev states. Spectroscopic studies of Andreev states have been performed in just a handful of systems. The unique geometry, electronic structure and high mobility of graphene make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor–graphene–superconductor junctions. The measured energy spectra, which depend on the phase difference between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between different mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent–phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson effect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials.

]]>Authors: Eva-Maria Roller, Lucas V. Besteiro, Claudia Pupp, Larousse Khosravi Khorashad, Alexander O. Govorov & Tim Liedl

Plasmonic nanoparticles hold great promise as photon handling elements and as channels for coherent transfer of energy and information in future all-optical computing devices. Coherent energy oscillations between two spatially separated plasmonic entities via a virtual middle state exemplify electron-based population transfer, but their realization requires precise nanoscale positioning of heterogeneous particles. Here, we show the assembly and optical analysis of a triple-particle system consisting of two gold nanoparticles with an inter-spaced silver island. We observe strong plasmonic coupling between the spatially separated gold particles, mediated by the connecting silver particle, with almost no dissipation of energy. As the excitation energy of the silver island exceeds that of the gold particles, only quasi-occupation of the silver transfer channel is possible. We describe this effect both with exact classical electrodynamic modelling and qualitative quantum-mechanical calculations. We identify the formation of strong hotspots between all particles as the main mechanism for the lossless coupling and thus coherent ultrafast energy transfer between the remote partners. Our findings could prove useful for quantum gate operations, as well as for classical charge and information transfer processes.

]]>Authors: L. Seiffert, Q. Liu, S. Zherebtsov, A. Trabattoni, P. Rupp, M. C. Castrovilli, M. Galli, F. Süßmann, K. Wintersperger, J. Stierle, G. Sansone, L. Poletto, F. Frassetto, I. Halfpap, V. Mondes, C. Graf, E. Rühl, F. Krausz, M. Nisoli, T. Fennel, F. Calegari & M. F. Kling

The scattering of electrons in dielectric materials is central to laser nanomachining, light-driven electronics and radiation damage. Here, we demonstrate real-time access to electron scattering by implementing attosecond streaking spectroscopy on dielectric nanoparticles: photoelectrons are generated inside the nanoparticles and both their transport through the material and photoemission are tracked on an attosecond timescale. We develop a theoretical framework for attosecond streaking spectroscopy in dielectrics and identify that the presence of the internal field inside the material cancels the influence of elastic scattering, enabling the selective characterization of the inelastic scattering time. The approach is demonstrated on silica nanoparticles, where an inelastic mean-free path is extracted for 20–30 eV. Our approach enables the characterization of inelastic scattering in various dielectric solids and liquids, including water, which can be studied in the form of droplets.

]]>Authors: Annafrancesca Rigato, Atsushi Miyagi, Simon Scheuring & Felix Rico

Living cells are viscoelastic materials, dominated by an elastic response on timescales longer than a millisecond. On shorter timescales, the dynamics of individual cytoskeleton filaments are expected to emerge, but active microrheology measurements on cells accessing this regime are scarce. Here, we develop high-frequency microrheology experiments to probe the viscoelastic response of living cells from 1 Hz to 100 kHz. We report the viscoelasticity of different cell types under cytoskeletal drug treatments. On previously inaccessible short timescales, cells exhibit rich viscoelastic responses that depend on the state of the cytoskeleton. Benign and malignant cancer cells revealed remarkably different scaling laws at high frequencies, providing a unique mechanical fingerprint. Microrheology over a wide dynamic range—up to the frequency characterizing the molecular components—provides a mechanistic understanding of cell mechanics.

]]>Authors: Yiqiu Ma, Haixing Miao, Belinda Heyun Pang, Matthew Evans, Chunnong Zhao, Jan Harms, Roman Schnabel & Yanbei Chen

]]>Authors: Martin Gärttner, Justin G. Bohnet, Arghavan Safavi-Naini, Michael L. Wall, John J. Bollinger & Ana Maria Rey

]]>Authors: L. D. Tóth, N. R. Bernier, A. Nunnenkamp, A. K. Feofanov & T. J. Kippenberg

]]>Authors: Po-Yao Chang, Onur Erten & Piers Coleman

]]>Authors: Zhenyu Wang, Daniel Walkup, Philip Derry, Thomas Scaffidi, Melinda Rak, Sean Vig, Anshul Kogar, Ilija Zeljkovic, Ali Husain, Luiz H. Santos, Yuxuan Wang, Andrea Damascelli, Yoshiteru Maeno, Peter Abbamonte, Eduardo Fradkin & Vidya Madhavan

]]>Authors: S. Peli, S. Dal Conte, R. Comin, N. Nembrini, A. Ronchi, P. Abrami, F. Banfi, G. Ferrini, D. Brida, S. Lupi, M. Fabrizio, A. Damascelli, M. Capone, G. Cerullo & C. Giannetti

]]>Authors: Sang Mo Yang, Anna N. Morozovska, Rajeev Kumar, Eugene A. Eliseev, Ye Cao, Lucie Mazet, Nina Balke, Stephen Jesse, Rama K. Vasudevan, Catherine Dubourdieu & Sergei V. Kalinin

]]>Author: Steven T. Bramwell

Assigning dimensions to physical quantities is not just for practicality. Steven T. Bramwell reflects on the deeper physical connotations of it all.

]]>