LR11774BR
Dissipationless flow of electrons---one by one
Electrons can flow without dissipation between two superconductors in
close proximity by transferring a pair of electrons---known as Cooper
pairs---at a time, a phenomena known as Josephson effect. We
theoretically discovered a dissipationless one-by-one electron
transfer from one superconductor to the other giving rise to
``fractional Josephson effect''. This occurs when the two neighboring
superconductors are connected by a new state of matter called a
topological insulator, which was theorized in 2005 and experimentally
discovered a year ago. The usual two-charge transfer occurs because
two electrons tend to bind together and form a Cooper pair inside a
superconductor. The new single-charge transfer that we predict is
possible because an individual electron finds an extra zero energy
"Majorana bound state" to stay at the interface between the
superconductor and the topological insulator. Our prediction can be
readily tested in future experiments
***
LX11765
Imaging Beyond the Diffraction Limit by Resistive means
Diffraction sets a fundamental limit to the resolution of an imaging system, restricting the ability to discriminate objects smaller than a wavelength. Here we present an approach for subwavelength imaging using a mundane conducting film as a natural optical superlens. It is theoretically predicted that near field sub–diffraction-limited imaging is possible as the film allows the recovery of critical evanescent waves that define a sharp image. This happens because space acts like a low pass filter for highly evanescent field components, and if a sheet or thin layer of imperfectly conducting material is placed adjacent to a source, such that the layer overcomes the larger impedance of the spatial low pass filter, no relative attenuation of evanescent components is experienced at the location of the sheet, resulting in a very sharp image (spot sizes of roughly 5% of the illumination wavelength are observed). The conducting layer enables us to trade definition for amplitude. Impedance sheets are commonplace in RF/microwaves, hence the phenomenon identified here is widespread, and can be easily extended into the Infrared and Terahertz regions, as well as to other areas of Physics where wave motion exists.
***
LW11257B
Spontaneous localization of dynamic energy in a simple ionic crystal
It has been shown over the last decade that driving a discrete
nonlinear lattice can cause dynamical energy to spontaneously
localize. A fundamental question in condensed-matter sciences and
nonlinear dynamics is whether or not such intrinsic localized modes
(ILMs) can appear in an atomic lattice in thermal equilibrium.
Neutron scattering measurements of He-4 and in alpha-U at high
temperatures have indicated new modes, possibly attributable to ILMs,
but these interpretations remain speculative since realistic models
of the nonlinear lattice dynamics are not available. These systems
are also exceptional in that both exhibit many exotic phenomena;
alpha-U is the only element to exhibit a charge density wave and
solid bcc He-4 is a quantum solid. The occurrence of new modes in
either of these systems, while interesting, does not have broad
implications since the underlying cause is related to rather unique
properties. By contrast, here we report the experimental observation
of ILMs in a remarkably simple ionic crystal, NaI, at high
temperatures and further show that these results are consistent with
realistic molecular dynamic simulations. Our work presents the first
observation of intrinsic 3-D localization requiring only discreteness
and nonlinearity in an atomic solid.
***
LZ11265AJ
Can relativity bother quantum cryptography?
Modern physics is dominated by quantum mechanics and relativity.
This is fair to say that Bell inequalities probe one of the deepest
aspects of quantum mechanics. The genesis of the Bell's discovery
can be traced back to the Einstein, Podolsky and Rosen seminal
paper about the completeness of quantum mechanics. They have
argued there that quantum mechanics would not provide a complete
description of nature if locality is assumed. Quantum mechanics
had to wait thirty years to be vindicated by John Bell who introduced
the inequalities which allow to test quantum mechanics against
competitive local hidden variable theories. If the spooky quantum
mechanical effect named entanglement [where non-causally related
particles can influence one another (see PHYSICAL REVIEW FOCUS,
27 December, "Spooky at any speed")] were correct, Bell inequalities
would be necessarily violated. Remarkably Bell inequalities have
been shown to be violated by 30 standard deviations, which strongly
supports quantum mechanics.
On the other hand, the fact that causally disconnected particles
can influence one another if they are quantum mechanically entangled
has raised an intense debate on the interplay between relativity and
quantum mechanics. In our work "Influence of detector motion in Bell
inequalities with entangled fermions", we investigate how relativity
influences the spin correlation of entangled fermions measured by
moving detectors. Suppose the physical situation where two entangled
spin-1/2 electrons described by wave packets fly in opposite directions.
At some point when they are far away one from the other (and thus
causally disconnected) each particle finds a spin detector. Although
actual experiments confirm that Bell inequalities are violated as
predicted by quantum mechanics when the detectors lie at rest,
we show that quantum mechanics will predict a quite different
output if the left and right spin detectors are set in fast enough
relativistic motion, namely, the CHSH Bell inequality will be
*satisfied* rather than violated.
Entanglement of quantum systems is currently used in many applications
including quantum cryptography protocols which is beginning to be
commercially traded. As technology develops, we expect that
quantum cryptography will be used to exchange messages around
the globe with the help of satellites. Because they move fast with
respect to the Earth surface, our work anticipates that relativity
should play some role here. This is difficult to anticipate at this
point whether or not this is going to be a protagonist one as in the
GPS case.
***
BZ10846
Listening to Underground Phonons
Ultrathin metal films on stiffer substrates can guide various kinds of
sound waves, some travelling at the surface, some underneath, and some at
the interface with the substrate. Not just the surface waves, largely
exploited in surface acoustic wave (SAW) devices, but especially their
sub-surface companions promise a future in novel electro- and
opto-acoustic devices, thus widely extending their application spectrum.
However, the rich family of sub-surface phonons remained so far elusive to
current surface probes such as electron energy loss spectroscopy. It comes
now as a surprise that the gentlest of all surface probes, helium atom
beams, can actually measure the dispersion of most sub-surface phonons.
Although He atoms merely tickle the surface a few Ångstroms above the
topmost atoms, they perceive the motion of the underground atoms via the
electron density oscillations at the surface. This mechanism, first
pinpointed in a previous study on the surface of copper, is now found
to work best with ultrathin lead metal films. Its electrons are highly
responsive to atomic motion making lead the element with the second
highest superconducting transition temperature (7.23K). Since this
responsiveness, shared by most metals, governs many thin-film transport
phenomena, measuring underground phonons is not only a significant step in
surface spectroscopy, but also points the way towards new nanometric
devices.
