LW12620

Superconducting quantum computing leaps ahead

Atoms and molecules jump abruptly between discrete quantum levels when observed. For the first time, we have seen the same phenomenon in a macroscopic electrical circuit – an “artificial atom” — engineered to exhibit quantum behavior. The key to the success of the experiment was the development of a new type of amplifier. Just like a fancy stereo allows one to hear the subtleties of a musical piece, our ultra-low noise amplifier enabled us to see the delicate quantum dance of our “artificial atom”. Both the amplifier and the “artificial atom” were constructed using superconducting circuits made out of aluminum and cooled to a fraction of a degree above absolute zero. The combination of low loss in the superconductor and the extremely low temperatures enabled the electrical circuit to display quantum behavior. This is a major step for solid-state quantum computing as high fidelity measurements of this type are crucial for correcting errors in a quantum computer. Such computers would harness quantum physics to perform calculations and promise to be more powerful than any non-quantum computer that could ever be built.



***

BZR1120

Controlling the charge state of nitrogen-vacancy centers

In our recent study, we managed to control and switch the charge state and, consequently, the color of nitrogen-vacancy (NV) centers in diamond. The NV center, which lends its color to some gemstone diamonds, is a lattice defect with an ionization energy within the diamond bandgap. Due to their suitable optical properties, NV centers are promising candidates for qubits and highly sensitive magnetic field sensors. Up to date, most of research has been focused on the naturally more abundant, negatively charged and purple-colored NV- state of these
centers.

We now demonstrated a controlled way to convert these negatively charged centers into their neutral state NV0. To achieve this, we focused on shallow centers which were implanted only few nanometers under the diamond surface. In this region, the Fermi level depends strongly on the surface termination. By terminating the diamond surface with hydrogen, we managed to lower the Fermi level below that off NV-, so that ionization into NV0 became favorable. This result, changing the color of a diamond from purple to yellow, is not only aesthetic, but will also enable a detailed understanding of the neutral change state of NV centers. Furthermore, the controlled alteration of the charge of NV centers described in our work is a crucial step towards the demonstration of the electronic control of the charge state of single NV centers in diamond, and thus opening attractive alternatives for the realization of diamond-based quantum computers.

***

LZ12582

Intergalactic alcohol probes drifting constants

In this Letter we propose to use methyl alcohol (CH3OH) for probing the variation of the proton-to-electron mass ratio. Methyl alcohol is one of the simplest molecules that exhibits internal rotation; the methyl (CH3) group rotates with respect to the alcohol (OH) group. In addition, the molecule rotates as a whole. We found that microwave transitions that convert the internal rotation to overall rotation – and vice versa – are very sensitive to the proton-to-electron mass ratio. When the proton-to-electron mass ratio changes by a certain fraction, the resulting fractional frequency change in methyl alcohol is up to 50 times this fraction. This is an order of magnitude larger than the transitions used so far in searches for possible spatial of temporal variations of the proton-to-electron mass ratio.

***

LX12353

COULD RELIC GRAVITONS BE LEFT-HANDED?

Could the graviton be more like the neutrino, which is only
present in Nature in a left-handed version? The possibility of
gravitational handedness has long been entertained in Ashtekar's
formulation of quantum gravity. In our Letter we reevaluated the
mechanism producing gravitational waves in the early Universe.
Relic gravitational waves are generated as microscopical vacuum
quantum fluctuations, which are then stretched to cosmological
sizes by a period of accelerated expansion. We found that
Ashtekar's formulation, while predicting equivalent right and left
handed graviton states, leaves a distinctive parity violating mark
in their vacuum fluctuations. At its most extreme it could be that
only right or left handed gravitons are produced in the early
Universe. Such a "chiral'' background of gravitational waves
would have a dramatic observational fingerprint. Current and
upcoming cosmic microwave background experiments focus on its
polarization. It is known that one particular polarization
component can only be produced by gravitational waves. But more
importantly, some polarization measures are non-zero only if, in
addition, the gravitational wave background is chiral. Therefore
the effect reported here could open up the doors of
experimentation to quantum gravity, at long last.



***

BZ11478

New Experimental Opportunities for Studying Structure and Atomic Mobility of Melts

A novel electrostatic levitation furnace for neutron scattering experiments on melts has been developed. The electrostatic levitation technique allows processing and melting of both electrically conductive and insulating materials under high vacuum conditions. By this containerless technique even chemically reactive melts can be investigated at high temperatures as well as in the undercooled liquid below the melting temperature. The avoidance of crucible materials in the vicinity of the freely suspended sample (see figure) results in an excellent signal-to-background ratio in scattering experiments. To enable appropriate scattering rates we increased the typical sample volume by one order of magnitude as compared to former generations of electrostatic levitators.

First experiments using the electrostatic levitator allowed us to investigate glass-forming Zr-Ni melts by neutron diffraction and quasielastic neutron scattering in a broad temperature range in the stable melt above the melting point and in the undercooled regime nearly 200 K below the melting temperature, determining structure factors and Ni self-diffusion coefficients. We demonstrate that this new approach results in a significant improvement of the quality of the data and an increased range of accessible temperatures.

***

EW10532

Electrical memory in human skin

In this paper electrical conductance in human skin is shown to display some memory of its electrical history. This can only be understood by using a newly realized, yet fundamental, memory element in electrical theory, namely the so-called memristor. Memristors clarify basic electrical circuit theory, complementing resistors, capacitors and coils. We show that the memristor is a good candidate for explaining many very important bioelectrical phenomena that are yet not fully understood. In particular, this holds for transport of ions in capillaries and pores, systems that are very common in living systems as well as in other solid state materials. Such flow of ions is important and a prerequisite for living cells as well as for many other biological processes. In overall, the memristor is shown to open a neglected field in bioelectricity, and hence is expected to be of particular interest in the future.


***

LX12388

Giant Gamma-Ray Bubbles are as Old as Galaxy

Recently NASA announced the startling discovery by its orbiting gamma-ray telescope, Fermi, of two enormous gamma-ray emission structures that hang like lightglobes above and below the centre of the Milky Way. These `Fermi bubbles' extend an astounding 30 thousand lightyears from the plane of the Galaxy. Thus far the Bubbles have been understood as illuminated by a mysterious population of youthful and highly energetic electrons. In this astrophysics context, `youthful' means an age of 10 million years or so. Now astrophysicists assert that the Bubbles have been inflated and illuminated by a wind of cosmic ray nuclei and super-hot plasma that has been blowing out of the centre of the Galaxy for almost 10 _billion_ years. This wind is driven by the sustained star-formation that has occurred in the Galactic nucleus since the youth of the Milky Way. In fact, the Bubbles constitute a perfect calorimetric recording of Galactic centre activity over the history of the Galaxy.


***


LT12340

Damage to DNA achieved gently, but effectively!

While it has long been established that damage to DNA occurs upon irradiation by energetic gamma rays and x-rays, results of laser-based experiments of DNA plasmids in liquids now reveal that disruption of DNA structure can also be induced by very low-energy electrons and radicals like OH. Exposure of a mixture of DNA and water to ultrashort pulses (lasting only a few tens of femtoseconds) of high-intensity laser light gives rise to the formation of low-energy electrons and OH radicals as water molecules undergo ionization and break-up. The resulting low-energy fragments have been shown to induce nicks in the DNA structure, with the OH radicals being about four times more effective in inducing damage than electrons. These findings may have implications in the use of high-intensity lasers in biomedical applications like laser surgery.

LY12164

Rebuilding a pulse of light in space and time

Multiple light scattering in disordered materials such as paint, paper or biological tissue breaks apart a laser pulse in space and time, a process that appears to be completely irreversible. In this Letter, we demonstrate that the reverse is possible: by spatially structuring broad-band light incident on a scattering medium, we are able to rebuild an intense ultra-short laser pulse from the fragments of the scattered light. The new method to control light in space and time has promising applications in imaging, sensing, and selective destruction inside opaque materials. Moreover, it will greatly enhance control of light when combined with new optical structures such as nanophotonic devices and metamaterials.


***

LW11796E

Boiling on the nanometer scale

Interaction of ultra-short laser pulses with solid state is still not completely understood although studied for several decades. According to the commonly-accepted theory, after the pulse is absorbed by the metal surface, the temperature of the latter increases and the metal melts, evaporates, and solidifies again. The remarkable feature of this process is that the temperature increases faster than the liquid metal can start boiling. As the result, a thin layer of superheated liquid metal appears on the surface. In this paper we demonstrate self-organized pattern appearing by explosive boiling of thin films of superheated melts. As the surface temperature decreases below the melting point, the still boiling liquid solidifies and the pattern gets frozen and can be studied afterwards by mean of common experimental tools like electron microscopy. The characteristic length scale of the pattern is in the range of several hundred nanometers and can be easily tuned in the experiments by changing the laser energy. Due to this property the self-organized nanopatterns could be of interest for nanotechnology.

***

LU12747 and DX10739

Solution of Cosmology's Biggest Problem Suggests A New View of Time

Did the past happen as we remember it? A new solution to one of
cosmology biggest problems suggests not. For thirteen years, we have
known that the expansion of the Universe is being accelerated by a
mysterious `dark energy’. The simplest explanation of this dark
energy is Einstein’s cosmological constant, Lambda, a form of energy
that fills the vacuum and drives the universe apart. However, there
is a problem with Lambda: it is some 123 orders of magnitude smaller
than we expect it to be. Not only is Lambda very small, but it also
defines a fundamental time scale that is, coincidently, the same
magnitude as the current age of the Universe. This remarkable
coincidence and the smallness of Lambda represent the biggest unsolved
problem in cosmology today: the cosmological constant problem. In
our PRL letter and PRD article we present a new solution to this
problem that avoids small numbers, does not require new and undetected
forms of matter, and which is subject to a high precision test in the
near future. Excitingly, our solution implies an radical new
understanding of time in which our past, and remembrance of it, slowly
changes over time.


***

LY12463

Creasing to Cratering under Voltages

A team of researchers has observed, for the first
time, the creasing to cratering instability in polymers under
electrical voltages. When bread dough is raised in a bowl, the top
surface of the dough may fold upon itself to form creases due to
compressive stresses developed in the dough. Surprisingly, this
phenomenon may be related to failures of electrical polymers that are
widely used in energy-related applications. Subjected to a voltage, a
substrate-bonded polymer film develops a biaxial compressive stress
parallel to the film. When the voltage reaches a critical value, the
compressive stress induces a pattern of creases on the polymer. If the
voltage further rises, the creases strikingly evolve into craters in
the polymer, as the electrical stress pulls the creases open. Polymers
usually breakdown electrically immediately after the creasing
instability, which can cause failures of insulating cables and organic
capacitors. The team innovatively introduces a protective layer
right beneath the polymer film. The protective layer prevents the
electrical breakdown, but allows the team to observe the creasing to
cratering instability for the first time.

***

LY12048

Detecting Vanishing Dimensions Via Primordial Gravitational Wave Astronomy

Lower-dimensionality at higher energies has manifold theoretical advantages
as recently pointed out - it removes the standard model hierarchy problem,
enables much easier quantization of gravity, and allows one to attack the
cosmological constant problem in a completely new way. Moreover, it appears
that experimental evidence may already exists for it - a statistically
significant planar alignment of events with energies higher than TeV has
been observed in some earlier cosmic ray experiments. If the dimensional
cross-over really happens at TeV scale, then one can make definite
predictions for the collider experiments. Finally, gravitational wave
astronomy enables a robust and independent test for this new paradigm. Since
(2+1)-dimensional spacetimes have no gravitational degrees of freedom,
gravity waves cannot be produced in that epoch in the history of the
universe. This places a universal maximum frequency at which primordial
waves can propagate, marked by the transition between dimensions. This
cut-off frequency is accessible to future gravitational wave detectors such
as LISA, which allows for a clear cut falsification or confirmation of this
paradigm.