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Twisted waves in a magnetoplasma (Vol. 48, No. 3)

Twisted wave propagating in a magnetized plasma along an arbitrary direction

In recent years, the properties of twisted light beams have been widely explored. In particular, it was realized that twisted laser beams are able to excite twisted density perturbations in a plasma, and that these density perturbations are indeed new forms of twisted waves. Each twisted wave solution is characterized by a topological charge. A further step in the understanding of twisted light was recently made, by studying twisted wave solutions in a magnetized plasma. This leads to a variety of twisted wave solutions, both electrostatic and electromagnetic, depending on the angle of propagation with respect to the static magnetic field. These waves can also be seen as quasi-particles, carrying an intrinsic angular momentum, which is determined by the value of their topological charge.

Furthermore, the kinetic description of a gas of such quasi-particles can also be established. This leads to a generalized concept of plasma turbulence, made of a gas of several types of twisted quasi-particles. An example of application was considered, where two twisted modes with different topological charge interact with each other, exchanging energy and angular momentum inside the plasma.

J. T. Mendonça and J. P. S. Bizarro, Twisted waves in a magnetized plasma, Plasma Phys. Control. Fusion 59, 054003 (2017)
[Abstract]

Two-loop self-energy correction in hydrogen Lamb shift (Vol. 42, No. 1)

image Comparison of the results of the numerical all-order calculations as a function of the nuclear charge Z (dots and solid line) and the analytical perturbative result (diamond on the y-axis) for the higher-order two-loop self-energy correction.

The results of the recent measurement of the Lamb shift in muonic hydrogen [R. Pohl et al., Nature 466, 213 (2010)] created what is now widely known as "the proton charge radius puzzle". The charge radius of the proton derived in this experiment turned out to be 4% smaller than that obtained from the Lamb shift in ordinary hydrogen. This discrepancy is very surprising, given that the underlying theory, QED, is one of the most precise and well-tested fundamental theories. Half a year has passed since the announcement of the unexpected results and theoreticians have checked and double-checked QED calculations in both muonic and ordinary hydrogen. However, despite all the efforts, no plausible ideas about the cause of the discrepancy have been suggested, and the puzzle remains unsolved.

This paper deals with the most problematic QED effect in ordinary hydrogen, the two-loop self-energy correction. It is this effect that induces the main theoretical error in the hydrogen proton charge radius. Previous calculations have demonstrated a disagreement between two different methods: the one based on the perturbative expansion in the binding nuclear field and the one including binding effects to all orders. Though this disagreement is too small to explain the puzzle, it still needs to be resolved to clarify the uncertainty of the hydrogen proton charge radius. In this paper, a new technique is developed for calculations of the two-loop self-energy diagrams treated in the mixed coordinate-momentum space. This technique increases the numerical accuracy of the results, reducing without eliminating the disagreement between the two approaches (Fig.).

The two-loop self-energy: diagrams in the coordinate-momentum representation
V.A. Yerokhin, Eur. Phys. J. D 58, 57-68 (2010)
[Abstract] | [PDF]

Two-site Bose-Hubbard model in waveguides (Vol. 42, No. 2)

image Optical realization of the two-site Bose-Hubbard model based on light transport in a waveguide array with engineered refractive index profile. The figure shows an example of Josephson oscillations in Fock space, in which light trapped in the various waveguides gives the occupation probability of the Fock states.

Light transport in waveguide lattices has provided over the past decade a test bench to visualize the classical analogues of a wide variety of coherent single-particle quantum phenomena generally encountered in condensed matter or matter wave systems. Since photons in linear optical structures do not interact, it is a common belief that the use of photonics as a model system for quantum physics carries the intrinsic drawback of being limited to visualize single-particle phenomena, missing the possibility to simulate the richer physics of interacting many-particle systems.

In this paper, the author has now pushed the realm of quantum-optical analogies beyond the single-particle phenomena, demonstrating that linear photonics can provide an accessible laboratory system to visualize in a purely classical setting the very basic dynamical aspects embodied in the physics of interacting quantum particles. In particular, a classical realization of the famous Bose-Hubbard Hamiltonian, which provides a paradigmatic model to describe the physics of strongly interacting bosons, has been theoretically proposed for light transport in engineered waveguide lattices. The author has shown that spatial propagation of light waves along the photonic crystal structure mimics in the Fock space the temporal dynamics of ultracold bosonic atoms trapped in a double-well potential, the so-called bosonic junction. While for ultracold atoms the full multi-particle dynamics is typically not accessible, the present work proposes a new route to simulate the Bose-Hubbard model which overcomes such a limitation, thus opening a new route to the realization of classical simulators of many-particle quantum physics.

Optical realization of the two-site Bose-Hubbard model in waveguide lattices
S. Longhi, J. Phys. B: At. Mol. Opt. Phys. 44 051001 (2011)
[Abstract] | [PDF]

Ultra-cold atom transport made simple (Vol. 45 No.4)

Schematic representation of the physical system consisting of a ring trap and two dipole waveguides for injecting neutral atoms into, extracting them from, and velocity filtering them in the ring waveguide. Credit: Loiko et al.

New study provides proof of the validity of a filtering device for ultra-cold neutral atoms based on tunnelling.

A new study gives a proof of principle, confirmed by numerical simulations, of the applicability to ultra-cold atoms of a very efficient and robust transport technique called spatial adiabatic passage (SAP). The authors have, for the first time, applied SAP to inject, extract, and filter the velocity of neutral atoms from and into a ring trap.

They focused on controlling the transfer of a single atom between the outermost waveguides of a system composed of two dipole waveguides and a ring trap, using the SAP technique. They calculated the explicit conditions for SAP tunnelling, which depend on two factors: the atomic velocity along the input waveguide and the initial atom population distribution among what physicists refer to as the transverse vibrational states.

To check the performance of the proposed approach, they relied on a numerical integration of the corresponding equation with parameter values for rubidium atoms and an optical dipole ring trap.

Y. Loiko, V. Ahufinger, R. Menchon-Enrich, G. Birkl and J. Mompart, “Coherent injecting, extracting, and velocity filtering of neutral atoms in a ring trap via spatial adiabatic passage”, Eur. Phys. J. D, 68, 147 (2014)
[Abstract]

Ultrafast laser for crafting ever thinner solar cells (Vol. 46 No. 2)

Interaction between ultrashort pulse laser and a target.

Solar-cell efficiency depends on how thin it can be manufactured. Now, a new model exploits femtosecond laser sources to get higher efficiency at lower cost.

The race for ever more efficient and cheaper solar cells tests the limits of manufacturing. To achieve this, photovoltaic solar cells need to become thinner and are made of more complex inner structures. Now, the authors have investigated and expanded a model elucidating the dominant physical processes when ultra-fast lasers are used in manufacturing solar cells to these specifications.

The authors rely on ultra-fast lasers, to develop a process called ablation, used to allow the formation of the metal contacts. It involves selectively removing the upper dielectric layer of the photovoltaic cell material without damaging the semiconductor beneath. Compared to previous methods, it offers many advantages—it reduces heat damage while improving the precision, energy efficiency and speed of the process.

A. Gurizzan and P. Villoresi, “Ablation model for semiconductors and dielectrics under ultrafast laser pulses for solar cells micromachining”, Eur. Phys. J. Plus 130, 16 (2015)
[Abstract]

Ultrafast x-rays capture the electron and nuclear dance (Vol. 49, No. 2)

Experimental techniques used in ultrafast x-ray science

There has been revolutionary progress in producing ultrafast short-wavelength radiation and dreams of visualizing electronic and nuclear motion in complex systems on their natural timescales are rapidly unfolding. Accelerator-driven free-electron-laser sources of ultrafast, ultraintense x-ray pulses that open the door to nonlinear multiphoton x-ray phenomena, though rare (seven worldwide), have basically doubled their operating number in the past year. Laboratory-based ultrafast x-ray pulses based upon high harmonic radiation from infrared lasers, present and affordable at many institutions, have decreased in pulse duration from a longstanding record of 67 attoseconds to 43 attoseconds recently, and, have increased in photon energy to >1 keV.

The roadmap presents independent perspectives from 17 leading groups on further source developments and their potential impacts on atomic and molecular physics. We start with familiar processes, i.e. ultrafast photoexcited molecular dynamics followed with femtosecond x-ray pulses, then discuss phenomena enabled only by intense x-ray pulses from the accelerator-based free-electron-laser sources, i.e. multidimensional x-ray spectroscopies, nonlinear scattering and single-shot imaging, and conclude with the attosecond frontier where new source developments enable fundamental understanding of how charge migrates and how electrons are ejected.

L. Young and 26 co-authors, Roadmap of ultrafast x-ray atomic and molecular physics, J. Phys. B: At. Mol. Opt. Phys., 51, 032003 (2018)
[Abstract]

Unfolding quantum jumps (Vol. 47 No. 2)

Example of a quantum trajectory displayed in real time (top) and in effective time (bottom)

A novel way of defining time parameterisation in continuous measurements sheds a new light on quantum jumps and helps unravel hidden phenomena.

The evolution of a continuously and weakly monitored quantum system is given by a quantum trajectory. The stronger the measurement gets, the less regular the trajectory becomes with the progressive emergence of seemingly instantaneous jumps and sharp spikes which make the analysis of this interesting regime difficult in practice. The authors have proposed to locally redefine time as a function of the measurement back-action in order to blow up the details which are lost in physical time. This new parameterisation unfolds quantum jumps which become continuous and provides a well defined strong measurement limit. This method yields a finer description than the standard von Neumann projective approach to strong measurements: anomalous observables that show non-zero fluctuations in the former would appear trivial in the latter. In addition to its theoretical interest, the technique presented has the advantage of being readily applicable to existing experimental datasets.

M. Bauer, D. Bernard and A. Tilloy, Zooming in on quantum trajectories, J. Phys. A: Math. Theor. 49, 10LT01 (2016)
[Abstract]

Unidirectional control of optically induced spin waves (Vol. 48, No. 4)

Optically induced spin waves propagating to the right.”

For future information technologies, the field of magnonics is rapidly emerging. Spin waves ̶collective modes of spin precessions ̶ are promising information carriers in magnonics, as Joule heating is negligible and propagation damping is low. Spatial control of the spin wave is indispensable for future application such as spin-wave switching, spin-wave-assisted recording, and sensing of small magnetic fields. In this article, unidirectional control of optically induced spin waves in a rare-earth iron garnet crystal is demonstrated. We observed the interference of two spin-wave packets with different initial phases generated by circularly polarized light pulses. This interference results in unidirectional propagation if the spin-wave sources are spaced apart at 1/4 of the wavelength of the spin waves and the initial phase difference is set to π/2. The propagating direction of the spin wave is switched by the polarization helicity of the light pulses. Moreover, in a numerical simulation, applying more than two spin-wave sources with a suitable polarization and spot shape, arbitrary manipulation of the spin wave by the phased array method was replicated. This achievement opens up a field of magnetic materials science and explores an alternative sensing technique using magnetic fields.

I. Yoshimine, Y. Y. Tanaka, T. Shimura and T. Satoh, Unidirectional control of optically induced spin waves, EPL 117, 67001 (2017)
[Abstract]

Uniformity: the secret of better fusion ignition (Vol. 45 No. 1)

Non-uniformity as a function of the power imbalance.

One of the ways to achieve thermonuclear fusion is through a controlled reaction between deuterium and tritium. The authors have made theoretical calculations indicating how best to improve the ignition stage of fusion reaction. This approach involves increasing the uniformity of irradiation using high-power laser beams on the external shell of a spherical capsule containing a mix of deuterium and tritium.

Reaching uniformity of irradiation matters for reaching the ignition conditions of thermonuclear fusion. In this study, the authors analyse the possibility of using the UK-based Orion facility’s high-power laser beams of to study uniformity. Specifically, the authors use numerical simulations to analyse the uniformity of the illumination of a spherical target both in the case of circular or elliptical laser intensity profiles. They demonstrate that this approach reduces considerably the non-uniformity of the capsule irradiation—by 50% and 35%, for elliptical and circular intensity profiles respectively.

M. Temporal, B. Canaud, W.J. Garbett, F. Philippe and R. Ramis, “Polar Direct Drive Illumination Uniformity Provided by the Orion Facility”, Eur. Phys. J. D, 67, 205 (2013)
[Abstract]

Universality in the symmetric exclusion process (Vol. 44 No. 6)

A system connected to two sources of heat or particles reaches, in the long time limit, a non-equilibrium steady state characterized by a non-vanishing and fluctuating current. Its study is an active topic in both classical and quantum systems. A relevant observable is the number Qt of particles flowing through the system during a time t. It can be calculated for simple models such as the symmetric simple exclusion process (SSEP), which describes two reservoirs at fixed densities connected by an L-site chain on which particles diffuse with a same site hard core repulsion. The corresponding cumulants of Qt are exactly known in one dimension and they coincide with those computed for the transport of free fermions through a mesoscopic conductor. We have generalized these results to arbitrary large but finite d-dimensional domains or graphs. Our numerical results indicate that, for large enough lattices and contacts to the reservoirs, the ratios of the cumulants of Qt take universal values, independent of the domain dimension and shape.

E. Akkermans, T. Bodineau, B. Derrida and O. Shpielberg, ‘Universal current fluctuations in the symmetric exclusion process and other diffusive systems, EPL, 103, 20001 (2013)
[Abstract]

Unlocking fuel cell conductivity (Vol. 44 No. 3)

Temperature dependence of conductivity data of bulk YSZ

Yttria stabilized zirconia, also known as YSZ, is a material of great interest because of its relatively high oxygen-ion based conductivity. In particular, it finds applications in electrochemical devices, such as solid oxide fuel cells and oxygen sensors. The present work developes a model of the oxygen-ion dynamics contributing to the conductivity of YSZ. The problem is that fuel cells currently operate above 700 ºC, which strongly limits their use. Understanding oxygen-ion diffusion is key in helping lower operating temperature towards ambient. Previous attempts to do so were done with the so-called coupling model (CM), describing simple physical concepts related to ion-ion interaction. This helped uncover the importance of ion-ion correlation in limiting long-range ion mobility, and thus conductivity.

The trouble is that experiments show that ionic conductivity in YSZ requires an activation energy that is much higher than that supplied by computer simulations describing independent ion hopping. Relying on the CM model, the authors first established a quantitative description of the ion dynamics in YSZ. Then they compared the predictions of the CM with experimental results and with simulations, particularly those of nanometric-scale thin films, published in the last ten years.

Thus, the present model establishes the connection between the level of the energy barrier for independent ion-hopping simulations and the level of activation energy of long-range oxygen ions measured experimentally. This model could also be used to study the conductivity relaxation of so-called molten, glassy and crystalline ionic conductors and ambient temperature ionic liquids.

K. L. Ngai, J. Santamaria and C. Leon, ‘Dynamics of interacting oxygen ions in yttria stabilized zirconia: bulk material and nanometer thin films’, Eur. Phys. J. B, 86, 7 (2013)
[Abstract]

Unpacking the mystery of Feynman’s reference amplifier (Vol. 51, No. 1)

Pixantrone thoroughly damages cancer cell DNA

A review of lectures given by Feynman between 1946 and 1971 showcase the strong influence that his involvement in the Manhattan Project held on his research, while revealing an intriguing mystery surrounding one particular amplifier device.

Richard Feynman was one of the 20th century’s most celebrated physicists. In 1943, he began his career in the Manhattan Project, where one of his tasks was to develop a device which could count the neutrons produced by nuclear reactions. Neutron signals emerging from counters must be strongly amplified to achieve this, but in the 1940s, practical amplification devices were hindered by their distorted signals. To overcome the issue, Feynman proposed a theoretical ‘reference amplifier’, which could provide amplifiers with a standard signal to be compared with. Through analysis published in EPJ H, researchers at the University of Naples, Italy, propose that this line of research exemplifies the influence which Feynman’s involvement in the Manhattan Project held over his later teaching and research.

V. d’Alessandro, S. Daliento, M. Di Mauro, S. Esposito, A. Naddeo, Searching for a response: the intriguing mystery of Feynman’s theoretical reference amplifier, European Physical Journal H 44, 331 (2019)
[Abstract]

Unresolved puzzles in exotic nuclei (Vol. 49, No. 3)

Closed points are matter radii extracted from experiments for isotopes of Helium (diamonds), Lithium (squares), and Beryllium (triangles)

A new review highlights the historical developments in our understanding of the nuclear structure of unstable and unbound forms of helium, lithium and beryllium

Research into the origin of elements is still of great interest. Many unstable atomic nuclei live long enough to be able to serve as targets for further nuclear reactions—especially in hot environments like the interior of stars. And some of the research with exotic nuclei is, for instance, related to nuclear astrophysics. In this review published recently, the author discusses the structure of unstable and unbound forms of Helium, Lithium, and Beryllium nuclei that have unusually large neutron to proton ratios—dubbed ‘exotic’ light nuclei. The author offers an account of historical milestones in measurements and the interpretation of results pertaining to these nuclei. The author also delineates some of the unresolved puzzles concerning the connection between microscopic structure and the values of quantities that are observable experimentally-- particularly the interplay between energies, widths or strengths and microscopic structure. For example, physicists have yet to resolve what is the occupancy of an orbital, called 2s1/2, in the ground state of beryllium-12? Or what is the nature of the unbound ground state of helium-10?

H. T. Fortune, Structure of exotic light nuclei: Z = 2, 3, 4, Eur. Phys. J. A, 54, 51 (2018)
[Abstract]

Unstable radioactive nuclei’s dual traits study in open refereed paper (Vol. 48 No. 1)

HIE-ISOLDE production yields.

HIE-ISOLDE acceleration of radioactive beams to peer into the dual state of matter unique to nuclei.

Radioactive nuclides, found within an atom's core, all share a common feature: they have too many or too few neutrons to be stable. In a new review published recently, the authors explain how overcoming technical difficulties in accelerating such radioactive nuclei beams can help push back the boundaries of nuclear physics research. This fascinating topic is the first EPJ A paper to be subjected to an open referee process, whereby the referee's comments are included. The authors outline how the new CERN project HIE-ISOLDE will reach the energy levels needed to make two nuclei overcome the electric repulsion between them—referred to as the Coulomb barrier. This means that it will be possible to design experimental tools to explore both single-particle and collective degrees of radioactive nuclei freedom. This will improve our understanding of the unique duality in the degrees of freedom, which no other state of matter exhibits. Ultimately, physicists aim to have a “dial-a-radioactive-nuclei beam” of the same quality as stable nuclei beams.

M.J.G. Borge and K. Riisager, HIE-ISOLDE, the project and the physics opportunities, Eur. Phys. J. A 52, 334 (2016)
[Abstract]

UV absorption spectroscopy to monitor reactive plasma (Vol. 42, No. 4)

image Absorbance of the HBr gas at three pressures, as used in silicon gate etching processes.

A new high sensitivity technique is developed by extending the broad-band absorption spectroscopy to the vacuum ultraviolet (VUV) spectral region. It is well adapted for the detection and density measurement of closed-shell molecules that have strong electronic transitions in the 110-200 nm range. Among them, molecules such as Cl2, HBr, BrCl, Br2, HCl, BCl3, SiCl4, SiF4, CCl4, SF6, CH2F2 and O2, used in the microelectronics industry for etching or deposition processes, are of prime interest. In our system, the light of a deuterium lamp crosses a 50 cm diameter industrial etch reactor containing the gas of interest. The transmitted light is recorded with a 20 cm focal length VUV scanning spectrometer backed with a photomultiplier tube (PMT). The attached figure shows the absorbance at three pressures of the HBr gas, which is used in silicon gate etching processes. Peaks at 137, 143 and 150 nm, which show a non-linear, but very strong absorbance, correspond to transitions to Rydberg states of the molecule and can be used for the detection of very small HBr densities. In our present experiment, an absorption rate of 2%, corresponding to about 0.03 mTorr of HBr, can be easily detected on the 143 nm absorption peak. Replacing the PMT detector by a VUV sensitive CCD camera, would permit to reach the same signal to noise ratio with a few seconds acquisition time. For HBr pressures in the 1 to 100 mTorr range, the continuum part of the absorption spectrum (160-200 nm), which shows a weak but linear absorbance can be used. The technique is applied to monitor in Cl2-HBr mixture the dissociation rate of HBr and the amount of Br2 molecule formation at different plasma conditions.

Vacuum UV broad-band absorption spectroscopy: a powerful diagnostic tool for reactive plasma monitoring
G Cunge, M Fouchier, M Brihoum, P Bodart, M Touzeau and N Sadeghi, J. Phys. D: Appl. Phys. 44, 122001 (2011)
[Abstract]

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