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LARES: a nearly ideal satellite to test fundamental physics (Vol. 44 No. 1)

The LARES satellite (courtesy of ASI)

The discovery of the accelerating expansion of the Universe, thought to be driven by a ‘dark energy’ constituting most of the Universe, has further revived the interest in testing Einstein’s theory of General Relativity (GR). Frame-dragging in the gravitational field generated by a rotating body or by a current of mass-energy is one of the most fascinating phenomena predicted by GR. The recently launched LARES (LAser RElativity Satellite) space mission is aimed at improving of about one order of magnitude the accuracy of the previous frame-dragging measurements by the LAGEOS and LAGEOS 2 satellites, using GRACE-derived Earth gravity determinations. After some years of orbital analysis of LARES, LAGEOS and LAGEOS 2 satellite laser-ranging data, frame-dragging should be tested within a few percents.

However, at the very foundation of Einstein’s theory is the geodesic motion of a small, structureless ‘test-particle’. Depending on the physical context, a star, planet or satellite can behave nearly like a test-particle, so geodesic motion is used to calculate the advance of the perihelion of a planet’s orbit and the dynamics of a binary pulsar system and of an Earth-orbiting satellite. Verifying geodesic motion is thus a test of paramount importance to GR and other theories of fundamental physics. On the basis of the first few months of satellite laser-ranging observations of the LARES satellite, its orbit shows the best agreement of any satellite with the test-particle motion predicted by GR. That is, after modelling its known non-gravitational perturbations, the orbit of LARES shows the smallest deviations from geodesic motion of any artificial satellite: its residual mean acceleration away from geodesic motion is less than 0.5 x 10-12 m/s2x. LARES-type satellites and accurate satellite laser ranging measurements can thus be used for further tests of gravitational and fundamental physics.

I. Ciufolini, A. Paolozzi, E. Pavlis, J. Ries, V. Gurzadyan, R. Koenig, R. Matzner, R. Penrose, and G. Sindoni, ‘Testing General Relativity and gravitational physics using the LARES satellite’, Eur. Phys. J. Plus , 133 (2012)
[Abstract]

Largest ever gas mix caught in ultra-freeze trap (Vol. 43 No. 2)

image Absorption images of the MOTs and the doubly-integrated optical density profile , recorded with a resonant imaging beam

The article summarised here leads to a better understanding of subatomic particles using a new cold-atom setup. The work make it easier to study atomic or subatomic-scale properties of the building blocks of matter (which also include protons, neutrons and electrons) known as fermions by slowing down the movement of a large quantity of gaseous atoms at ultra-low temperature.

Thanks to the laser cooling method for which Claude Cohen-Tannoudji, Steven Chu and William D. Phillips received the Nobel Prize in 1997, the authors succeeded in creating the largest Lithium 6 (6Li) and Potassium 40 (40K) gas mixture to date. The experimental approach involved confining gaseous atoms under ultra-high vacuum using electromagnetic forces, in an ultra-freeze trap of sorts.

This trap enabled them to load twice as many atoms than previous attempts at studying such gas mixtures, reaching a total on the order of a few billion atoms under study at a temperature of only a few hundred microKelvins (corresponding to a temperature near the absolute zero of roughly -273 °C).

Given that the results of this study significantly increased the number of gaseous atoms under study, it will facilitate future simulation of subatomic-scale phenomena in gases. In particular, it will enable future experiments in which the gas mixture is brought to a so-called degenerate state characterised by particles of different species with very strong interactions. Following international efforts to produce the conditions to study subatomic-scale properties of matter under the quantum simulation program, this could ultimately help scientists to understand quantum mechanical phenomena occurring in neutron stars and so-called many-body problems such as high-temperature superconductivity.

Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
A. Ridinger, S. Chaudhuri, T. Salez, U. Eismann, D. Rio Fernandes, D. Wilkowski, F. Chevy and C. Salomon, Eur. Phys. J. D, 65, 1-2. (2011) - cold quantum matter special issue.
[Abstract]

Laser detectors of possibly toxic gases (Vol. 44 No. 3)

Envelope function and two spectra illustrating the continuous tuning range of the realized single mode SMM VCSEL structures.

It is the increasing demand of safety at work and also at home, which acts as the driving force for new developments in nanotechnology and laser physics. Hazardous and toxic gases are representing maybe the most severe risk as being invisible, fast, deleterious and partially lethal in its effect. Handheld systems, which can be used for the on-site detection of these gases, are of huge interest these days. With the present Surface Micro Machined (SMM) Micro-Electro-Mechanical-System Vertical-Cavity-Surface-Emitting-Lasers (MEMS VCSEL) devices, the key technology for these systems has been realized. VCSELs are vertically emitting laser devices with extremely low thresholds but sufficiently high optical output power for gas sensing applications. A monolithically integrated membrane as top reflector on every single VCSEL device (described by the acronym MEMS) serves as deflectable element, which can be actuated both, electro-thermally and electro-statically. The generated air-gap underneath can be continuously changed by this technique and hence the emission wavelength. This enables continuous scanning over specific gas absorption lines. The present lasers are the first widely tunable ones in this wavelength range. Devices with 50 nm of continuous tuning, 50 dB of side mode suppression ratio (30 dB would already be sufficient for sensing applications), peak optical powers of 1 to 2 mW and extremely low threshold current densities of 2.2 kA/cm2 are perfect for this application.

T. Gruendl and 10 co-authors, ‘50 nm continuously tunable MEMS VCSEL devices with surface micromachining operating at 1.95 μm emission wavelength’, Semicond. Sci. Technol. 28, 012001 (2013)
[Abstract]

Laser-atom interacts: the electron at the mercy of the laser (Vol. 43 No. 3)

image Double-differential electron momentum distributions

The interaction between atoms and intense electromagnetic pulses with durations in the (sub) femtosecond time domain has proved to be a powerful tool to understand the dynamics of electrons inside matter. Among the theoretical methods developed to describe the electronic transitions produced by such ultrashort pulses we can mention the Coulomb-Volkov (CV) approximation, in which the combined action of both the atomic and laser potentials is taken into account only in the final channel. The CV approach has become a widespread method to investigate the physics behind photoinduced ionization processes. Nevertheless, it fails when the perturbative conditions are not fulfilled, for instance, when the ionization produced by an intense laser field takes place in an effective time much shorter than the pulse duration, or when the ionization requires multiphoton transitions.

Here we propose a doubly distorted CV (DDCV) model that goes beyond the standard CV theory by incorporating the effect of the laser field on both the initial and final electronic states on an equal footing. This improvement allows the method to account for dynamic Stark effects, which play an important role for long electron excursions originated by the laser electric field.

We found that the DDCV approach provides reliable predictions of photoinduced electron emission distributions from H(1s) for different field intensities and wavelengths, including a range of laser parameters where the CV approach is inadequate. In addition, the extension of the DDCV approximation to complex atoms and molecules appears to be perfectly viable.

Doubly-distorted-wave method for atomic ionization by ultrashort laser pulses
M. S.Gravielle, D. G.Arbó, J. E. Miraglia and M. F. Ciappina, J. Phys. B: At. Mol. Opt. Phys. 45, 015601 (2012)
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Laser-based accelerators: yes, we CAN! (Vol. 47 No. 1)

Cover picture of the EPJ Special Topic issue on the Science and the applications of the coherent amplifying network (CAN) laser
© Fraunhofer IOF
Jena, Germany, Bernd Müller

Future ultra-fast high power lasers, dubbed Coherent Amplification Network (CAN) lasers, will deliver unprecedented accelerating power and efficiency

Few technologies have the power that particle accelerator technology has to touch upon such a broad range of applications at the many frontiers of modern science. Today, thanks to improvements in laser technology, a new generation of accelerators could soon emerge to replace accelerators relying on radio frequencies. This special issue explores the requirements necessary to make such laser accelerators a reality, by presenting the work of the International Coherent Amplification Network (ICAN) research collaboration. The articles study: average/peak power and efficiency limits of coherently combined ultrafast laser systems; synchronization, spatial and temporal recombination of a large number of fibre amplifiers; temporal and spatial beam quality; combining efficiency of coherent addition amplitude and phase stability as a function of the number of fibres and their individual performance; and reduction of pulse duration and manipulation of pulse shape. Potential applications include future colliders, solutions for vacuum physics, design of Higgs-particle factories, and creation of sources of high-flux protons and of neutrons, among others. Further, such accelerators open the door to solutions in nuclear pharmacology and proton therapy as well as orbital debris remediation.

Science and applications of the coherent amplifying network (CAN) laser, Eur. Phys. J. Special Topics, 224, Number 13 (2015)
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Laser-based prototype probes cold atom dynamics (Vol. 51, No. 2)

Apparatus for cold atom inertial sensing.

A new prototype design doubles the frequencies of widely used telecommunications lasers to study the dynamics of cold atoms while in space.

By tracking the motions of cold atom clouds, astronomers can learn much about the physical processes which play out in the depths of space. In this work, an innovative prototype for a new industrial laser system is presented that paves the way for development of cold atom inertial sensors in space.

R. Caldani, S. Merlet, F.P. Dos Santos, G. Stern, A. Martin, B. Desruelle, V. Ménoret, A prototype industrial laser system for cold atom inertial sensing in space, European Physical Journal D 73, 248 (2019)
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Laser-ranged satellite measurement now accurately reflects Earth's tidal perturbations (Vol. 49, No. 2)

Lustbühel Satellite Laser Tacking. Credit: Jörg Weingrill (CC BY 2.0 [5])

The most precise ever laser satellite measurement method provides new clues to relativity

Tides on Earth have a far-reaching influence, including disturbing satellites’ measurements by affecting their motion. This disturbance can be studied using a model for the gravitational potential of the Earth, taking into account the fact that Earth’s shape is not spherical. The LAser RElativity Satellite (LARES), is the best ever relevant test particle to move in the Earth’s gravitational field. In a new study published, LARES proves its efficiency for high-precision probing of General Relativity and fundamental physics. By studying the Earth’s tidal perturbations acting on the LARES, the authors demonstrate the value of laser-range satellites for high-precision measurements.

V.G. Gurzadyan, I. Ciufolini, H.G. Khachatryan, S. Mirzoyan, A. Paolozzi, and G. Sindoni, On the Earth’s tidal perturbations for the LARES satellite, Eur. Phys. J. Plus 132, 548 (2017)
[Abstract]

Lasing with topological defects (Vol. 47 No. 1)

Scanning-electron microscope (SEM) images of the topological defect laser where a photonic crystal surrounds the optical cavity.

A new laser based on a swirling vortex of light has been created by the authors. The ‘topological-defect laser’ could be a useful addition to lab-on-a-chip devices, where it could manipulate fluids and tiny particles. The design could also be modified to create beams of light with orbital angular momentum.

Conventional lasers confine light by bouncing it back and forth in an optical cavity made of two opposing mirrors. The authors have taken a new twist on this design by making an optical cavity that confines light by having it swirl around in a vortex. They made their optical cavity within a photonic crystal, which is a material containing a regular array of elements which are separated by distances on par with the wavelength of light. Light at certain wavelengths and travelling in certain directions will pass freely through a photonic crystal, whereas light not meeting these criteria will be diffracted into a new trajectory.

S. Knitter, S. F. Liew, W. Xiong, M. I. Guy, G. S. Solomon and H. Cao, Topological defect lasers, J. Opt. 18, 014005 (2016)
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Lattice Improvement in Lattice Effective Field Theory (Vol. 50, No. 2)

The dimer-boson inverse scattering length $1/a{3}$ versus lattice spacing at LO, NLO, and N2LO. The vertical lines give the upper limits of the fit range

Lattice calculations using the framework of effective field theory have been applied to a wide range of few-body and many-body systems. One of the challenges of these calculations is to remove systematic errors arising from the nonzero lattice spacing. While the lattice improvement program pioneered by Symanzik provides a formalism for doing this and has already been utilized in lattice effective field theory calculations, the effectiveness of the improvement program has not been systematically benchmarked.

In this work lattice improvement is used to remove lattice errors for a one-dimensional system of bosons with zero-range interactions. To this aim the improved lattice action up to next-to-next-to-leading order is constructed and it is verified that the remaining errors scale as the fourth power of the lattice spacing for observables involving as many as five particles. These results provide a guide for increasing the accuracy of future calculations in lattice effective field theory with improved lattice actions.

N. Klein, D. Lee and U.-G. Meißner,, Lattice improvement in lattice effective field theory, Eur. Phys. J. A 54, 233 (2018)
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Law governing anomalous heat conduction revealed (Vol. 46 No. 5-6)

Heat conductance as the function of temperature T for different lattice size N = 50; 100; 200; 400; 800 and 1600

Study finds the law governing how heat transport scales up with temperature.

How heat travels, matters. Yet, there is still no consensus on the exact physical mechanism that causes anomalous heat conduction—despite the existence of previous numerical simulation, theoretical predictions and experimental observations. Now, the authors have demonstrated that electron transport depends on temperature. It follows a scaling governed by a power law—and not the exponential scaling previously envisaged. These findings were published recently. Heat conduction depends on the internal energy transferred by microscopic diffusion and collisions of particles, such as electrons, within a given body. Anomalous heat conduction can be best studied in a particular kind of model: one that accounts for the thermal transport in a one-dimensional (1D) lattice. In this study, the chosen 1D model is dubbed the coupled rotator lattice model. The authors systematically investigated how heat conductivity changes with temperature. This approach led them to the thesis that heat conductivity correlates with a power law, instead of an exponential scaling as previously predicted. Further, this phenomenon occurs without a transition temperature above which the heat conduction is normal and below which it is anomalous.

Y. Li, N. Li and B. Li, Temperature dependence of thermal conductivities of coupled rotator lattice and the momentum diffusion in standard map, Eur. Phys. J. B, 88, 182 (2015)
[Abstract]

Leidenfrost propulsion on a ratchet (Vol. 43 No. 1)

image Levitating Leidenfrost drop on a hot ratchet: a force acts on the drop, which deflects a fiber plunging in it.

The Leidenfrost phenomenon is observed when depositing liquids on solids much hotter than their boiling point. Liquids then levitate on a cushion of their own vapour, and slowly evaporate without boiling, due to the absence of contact with the substrate. The vapour cushion also makes liquids ultra-mobile, and Linke discovered in 2006 that Leidenfrost drops on a hot ratchet self-propel, in the direction of "climbing" the teeth steps. The corresponding forces were found to be 10 to 100 µN, much smaller than the liquid weight, yet enough to generate velocities of order 10 cm/s.

The origin of the motion was not really clear, despite stimulating propositions in Linke's original paper. As a first step, it was reported in 2011 by Lagubeau et al. that disks of sublimating dry ice also levitate and self-propel on hot ratchets: liquid deformations are not responsible for the motion. However, the levitating object in all these experiments squeezes the vapour below, and the resulting flow might be rectified by the asymmetric profile of the ratchet. The key question was not only to check this assumption, but also to determine in which privileged direction the vapour flows. By tracking tiny glass beads in the vapour, it was shown that rectification indeed takes place, along the descending slope of the teeth - the vapour escaping laterally once reaching the step of the teeth. Hence the levitating body is entrained by the viscous drag arising from this directional vapour flow. Goldstein et al. reached a similar conclusion in a paper to appear in the Journal of Fluid Mechanics. Many questions however remain: ratchets also generate special frictions (the liquid hits the teeth as it progresses), and the optimal ratchet (maximizing the speed of these little hovercrafts) has not yet been designed.

Viscous mechanism for Leidenfrost propulsion on a ratchet
G. Dupeux, M. Le Merrer, G. Lagubeau, C. Clanet, S. Hardt and D. Quéré, EPL, 96, 58001 (2011)
[Abstract]

Lifshitz transitions and correlation effects in unconventional superconductors (Vol. 47 No. 2)

Calculation of the effective mass as a function of thermal energy and the shift of the top of a hole pocket (Et) relative to the Fermi energy

Unconventional superconductivity is observed in heavy fermion systems, cuprates, molecular crystals, and iron-based superconductors close to a point in the phase diagram where as a function of a control parameter (pressure or doping), the antiferromagnetic order is suppressed. A widespread view is that at this point, which is called a quantum critical point (QCP), strong antiferromagnetic fluctuations are a candidate for the glue mediating superconductivity and also account for the normal state non-Fermi-liquid behaviour. Recent ARPES results on ferropnictides have shown that in these compounds the non-Fermi-liquid like scattering rate does not diverge at the QCP, as expected in the quantum critical scenario. Rather, near the QCP it is constant over a large range of the control parameter. In this study, a new scenario is proposed using minimum model calculations: a co-action of hole vanishing Lifshitz transitions and correlation effects is able to explain the ARPES results as well as the strange normal state transport and thermal properties.

J. Fink, Influence of Lifshitz transitions and correlation effects on the scattering rates of the charge carriers in iron-based superconductors, EPL 113, 27002 (2016)
[Abstract]

Like a game of 'spot the difference' for disease-prone versus healthy people (Vol. 48, No. 5-6)

Dynamical behaviour of different low-density lipoproteins as a function of temperature and pressure

The change in behaviour of natural nanoparticles, called lipoproteins, under pressure could provide new insights to better understand the genesis of high cholesterol and atherosclerosis

Understanding common diseases sometimes boils down to grasping some of their basic mechanisms. For instance, a specific kind of natural nanoparticles, called low-density lipoproteins (LDL), are fascinating scientists because their modification plays a key role in people affected by high cholesterol. They are also known for their role in the formation of atherosclerosis. The authors mimicked variations of LDL found in people affected by such diseases. They then compared their responses to temperature variations and increased pressure with those of lipoproteins found in healthy people. Their findings, recently published, show that the LDL from healthy people behaved differently when subjected to high pressure compared to LDL affected by the common diseases studied. The authors found that when LDL particles were subjected to variations in temperature, their behaviour was very similar. In fact, a rise in temperature increased their dynamics at the molecular level. However, when the authors increased the pressure on LDL particles, they found that their flexibility actually increased under pressure in healthy people. By contrast, their flexibility clearly decreased for the two modified forms mimicking disease states. This difference, the authors believe, could stem from a slightly different lipid composition.

J. Peters, N. Martinez, B. Lehofer and R. Prassl, Low-density lipoproteins investigated under high hydrostatic pressure by elastic incoherent neutron scattering, Eur. Phys. J. E 40, 68 (2017)
[Abstract]

Liquid foam: plastic, elastic and fluid (Vol. 47 No. 2)

Snapshot of a foam in a convergent channel

New study elucidates the plastic flows behind the motion of liquid foams, whose ability to absorb all kinds of waves makes them well-suited as acoustic insulators, or as explosion wave absorbers.

What differentiates complex fluids from mere fluids? What makes them unique is that they are neither solid nor liquid. Among such complex fluids are foams. They are used as a model to understand the mechanisms underlying complex fluids flow. Now, the authors have gained new insights into predicting how complex fluids react under stretching conditions due to the interplay between elasticity, plasticity and flow. These findings were recently published by the authors. Ultimately, potential applications include the design of new, optimised acoustic insulators based on liquid forms, or the mitigation of blast waves caused by explosions.

B. Dollet and C. Bocher, Flow of foam through a convergent channel, Eur. Phys. J. E 38, 123 (2015)
[Abstract]

Liquid jets break up more readily on a substrate (Vol. 50, No. 3)

Liquid jets break up more readily on a substrate
Filaments

Using computational models to investigate how liquid drops behave on surfaces

Whether we're aware of it or not, in day-to-day life we often witness an intriguing phenomenon: the breakup of jets of liquid into chains of droplets. It happens when it rains, for example, and it is important for inkjet printers. However, little is known about what happens when a liquid jet, also known as a liquid filament, breaks up on top of a substrate. According to a new study, the presence of a nearby surface changes the way the filament breaks up into smaller droplets. In a new paper published recently, computer simulations are used to show that a filament is more likely to break up near a surface. When a filament is broken into multiple droplets, the structure is unstable because surface tension means liquids tend to shrink to have the smallest-possible surface area.

A. Dziedzic, M. Nakrani, B. Ezra, M. Syed, S. Popinet, and S. Afkhami (2019), Breakup of finite-size liquid filaments: Transition from no-breakup to breakup including substrate effects, Eur. Phys. J. E 42 ,18 (2018)
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