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Bell’s equations enable scientists to test the fundamental implications of quantum physics. A central tenet of this idea is that the choice of measurement is truly random. Researchers now show that some Bell experiments can even increase randomness in cases where choice is not entirely free. The concept could increase the usefulness of weakly random sources for more thorough tests of quantum mechanics.
The proximity effect enables the injection of Cooper pairs from a superconductor into a normal metal, but they usually do not travel far into the metal. A study of the propagation of Cooper pairs from irregularly shaped superconducting islands on a metal film finds that they can travel further than expected for certain island geometries.
Despite their name, the bulk electrical conductivity of most topological insulators is relatively high, masking many of the important characteristics of its protected, surface conducting states. Counter-doping reduces the bulk conductivity of Bi2Se3 significantly, allowing these surface states and their properties to be clearly identified.
An interferometric implementation of Young’s double-slit experiment is used to probe quantum correlations that are manifest in the distribution of local spin fluctuations in a two-component degenerate Fermi gas.
Bose–Einstein condensation is usually considered to be an inherently quantum mechanical phenomenon. An observation of the condensation in a classical system of light waves in a nonlinear crystal demonstrates that it is a general wave-mechanical phenomenon.
Conventional approaches to optomechanics control and monitor the motion of nanoscale mechanical resonators by coupling it to a high-quality photonic cavity. An all-mechanical implementation is now demonstrated by creating a so-called phonon cavity from different oscillating modes of the resonator. This idea opens a route to using solid-state systems to investigate physics not accessible in their analogous, but better developed, quantum-optics counterpart.
An outstanding question about the iron-based superconductors has been whether or not their magnetic characteristics are dominated by itinerant or localized magnetic moments. Absolute measurements and calculations of the magnetic response of undoped and Ni-doped BaFe2As2 indicate the latter.
It is well known that graphene deposited on hexagonal boron nitride produces moiré patterns in scanning tunnelling microscopy images. The interaction that produces this pattern also produces a commensurate periodic potential that generates a set of Dirac points that are different from those of the graphene lattice itself.
A cross-validation study comparing experimental findings obtained with a system of ultracold fermions with the results of a method based on computing contributions from millions of Feynman diagrams underlines the potential of the so-called bold diagrammatic Monte Carlo technique for solving problems in the area of strongly correlated quantum matter.
The Cooper pairs of conventional superconductors exhibit a nodeless s-wave symmetry, and most unconventional superconductors, including cuprates and heavy-fermion materials, exhibit nodal d-wave pairing. In contrast to both, angle-resolved photoemission spectroscopy measurements indicate that the iron-based superconductor BaFe2(As0.7P0.3)2 exhibits an unusual nodal s-wave pairing.
Squeezed states—which permit precision beyond the scope of Heisenberg’s uncertainty relation—are well established for spin-1/2 particles. Now an elegant demonstration of squeezing in spin-1 condensates generalizes the criteria for squeezed states to higher spin dimensions.
Magnetic reconnection is a process by which the field lines of a magnetized plasma undergo dramatic realignment, releasing large amounts of energy. Large-scale simulations of reconnection events in the Earth’s magnetosphere suggest that this process takes place over much greater distances than previously expected.
An experiment demonstrates that the motion of so-called skyrmions—topologically quantized magnetic whirls—causes an emergent electric field that inherits the topological quantization of the skyrmions and is directly visible in the Hall effect.
The degree to which an electrical current is spin polarized is usually determined by how easily it travels across an interface with a magnetic contact. By using nonlinear interactions between spin and charge in graphene, the polarization of spin currents can be measured without magnetic contacts.
Liquid 3He in silica aerogel exhibits no trace of the chiral superfluid phase present in bulk 3He. Stretching the aerogel axially introduces an anisotropy that stabilizes the chiral phase, supporting a transition to a new disordered phase at low temperatures.
One proposed explanation of unconventional superconductivity involves describing it in terms of a crossover from a conventional superconducting state to a Bose–Einstein condensate state. Angle-resolved photoelectron measurements of an iron chalcogenide superconductor could provide evidence for such crossover behaviour.
Geomagnetic storms driven by the solar wind can cause a dramatic drop in the flux of high-energy electrons in the Earth’s outer Van Allen belt. Analysis of data obtained during such an event by three different sets of spacecraft suggests that these electrons are directed into space rather than lost to the atmosphere.
Measurements of Hanbury Brown and Twiss correlations in atomic gases near the Bose–Einstein condensation threshold reveal strong signatures of interactions between the constituent atoms, and establish such correlation measurements as a sensitive probe for the quantum properties of matter-wave sources.
A novel mechanism for cooling tiny mechanical resonators is now demonstrated. Inelastic scattering of light from phonons in an electrostrictive material attenuates the Brownian motion of the mechanical mode.
According to Heisenberg, the more precisely, say, the position of a particle is measured, the less precisely we can determine its momentum. The uncertainty principle in its original form ignores, however, the unavoidable effect of recoil in the measuring device. An experimental test now validates an alternative relation, and the uncertainty principle in its original formulation is broken.
