Volume 12 Issue 8, August 2016

Paul Ginsparg shares his thoughts about the future of the preprint server he created 25 years ago.

A movie of ultrafast electron dynamics driven by lightwaves shows that wide-bandgap semiconductors could form the building blocks of petahertz electronic devices.

Owing to the extreme sensitivity of a microscopic cantilever to optical forces, it is possible to uncover the fine structure of optical momenta and associated mechanical effects in evanescent fields.

Jammed states in growing yeast populations share intriguing similarities with amorphous solids, despite being generated through self-replication. The impact this behaviour has on cell division highlights one way that physical forces regulate biological function.

Due to their chirality, the massless fermions inside Weyl semimetals can take unusual paths that are governed by chiral dynamics, potentially providing a direct method to explore their topological nature.

The detection of a discrete knot of particle emission from the active galaxy M81* reveals that black hole accretion is self-similar with regard to mass, producing the same knotty jets irrespective of black hole mass and accretion rate.

An unexpected optical momentum and force perpendicular to the wavevector are measured using a nano-cantilever in an evanescent optical field, confirming a 75-year-old prediction.

The change in pitch of a passing car engine is a classic example of the translational Doppler effect, but rotational Doppler shifts can also arise, as shown for circularly polarized light passing through a spinning nonlinear optical crystal.

Experiments showing that electron dynamics can be controlled on attosecond timescales suggest that wide-bandgap semiconductors could be exploited for petahertz signal processing technologies.

A phenomenon known as magnetic fragmentation is observed by means of neutron scattering in the spin ice candidate Nd₂Zr₂O₇.

A scanning tunnelling microscopy study demonstrates that one-dimensional charge density waves can form at twin boundaries in a monolayer transition metal dichalcogenide.

The molecular motors that package DNA into viruses stall frequently under conditions promoting DNA–DNA attraction. Single-molecule experiments suggest the stalling is due to a nonequilibrium jamming transition induced by the attractive interactions.

Populations of growing yeast are shown to undergo a jamming transition typically observed in gravity-driven granular flows. The pressures generated by intercellular forces are found to be large enough to destroy the cells’ micro-environment.

The final stage of the Venus Express mission involved aerobraking — or deceleration by atmospheric drag — through the upper atmosphere above the northern pole of Venus. Concurrent measurements revealed two kinds of waves.

Radio and X-ray observations of the jet emission from M81^∗, the nearest low-luminosity supermassive black hole, reveal a knot structure. The knot is unexpected, as models generally assume a continuous and compact jet.

Entanglement in many-body systems is notoriously hard to quantify, but in certain situations relevant to atomic and condensed-matter experiments an entanglement witness, the quantum Fisher information, becomes measurable by means of the dynamic susceptibility.

Atoms in optical lattices are interesting for quantum technologies but engineering entanglement between atom pairs is difficult. Using the double-well potentials of a superlattice, the generation and detection of entanglement is more straightforward.

It takes extreme sensitivity to measure the elementary excitations in liquid helium-4. An optomechanical cavity with a thin film of superfluid inside can be used to both observe and control phonons in real time.

Defects affect materials’ properties. A method is now presented for studying dynamic processes during the growth of thin films — specifically, the evolution of defects — based on the coherent mixing of bulk and surface X-ray scattering signals.

Inertial confinement fusion, based on laser-heating a deuterium–tritium mixture, is one of the approaches towards energy production from fusion reactions. Now, record energy-yield experiments are reported—bringing us closer to ignition conditions.

The IceCube neutrino telescope in the South Pole has observed several high-energy neutrinos of undetermined origin. Could the third detected PeV event be from blazar PKS B1424–418?

Michel Van Camp and Olivier de Viron are attracted to the fluctuations in the Earth's gravitational pull.