Vol. 49 No.3 - Highlights
Disordered configurations of the Glauber model on two-dimensional networks (Vol. 49, No. 3)
The Glauber model provides a paradigm for modeling ordering processes in complex systems. The question that we answer is: How is the efficiency of the ordering process in the Glauber model affected if we rewire the links of the two-dimensional host lattice? Our research reveals that the fraction of disordered configurations exhibits a nonlinear dependence on the rewiring probability. In the small-world regime, the Glauber dynamics remains trapped in a metastable configuration that is disordered. In fact, we have observed a stationary state that consists of two intertwined domains of similar size, as shown in the figure. For higher rewiring probabilities, we observe isolated droplets of spins, which emerge due to poorly connected nodes in the network. We have also studied what happens to the ordering process on two-layer networks, in particular comparing outcomes on a multiplex network and on the corresponding network with random inter-layer connections. We have shown that, in this case, the properties of the stationary state are strongly affected by the type of inter-layer connections.
I. Baĉić, I. Franović and M. Perc , Disordered configurations of the Glauber model
in two-dimensional networks, EPL, 120, 68001 (2017)
Unresolved puzzles in exotic nuclei (Vol. 49, No. 3)
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)
High-energy ions’ movement affected by silicon crystal periodicity (Vol. 49, No. 3)
Thinnest-ever silicon crystal enhances ion channelling performance in particle accelerators.
The thinner the silicon crystal, the better. Indeed, thinner crystals provide better ways to manipulate the trajectories of very high-energy ions in particle accelerators. Further applications include materials analysis, semiconductor doping and beam transport in large particle accelerators. All of these rely on our understanding of how positively-charged high-energy particles move through crystals. This process, called ion channelling, is the focus of a new paper published recently. In this paper, the authors study how the crystal periodicity affects the motion of ions whose energy belongs to a 1 to 2 MeV range, as they are transmitted through very thin crystals on the order of a few hundred nanometres, and how it impacts their angular distribution. What is so interesting about this work is that it relies on an advanced process of fabricating much thinner crystals than was previously possible, reaching 55 nanometres. This, in turn, makes it possible to observe much more sensitive and fine angular structures in the distribution of transmitted ions.
M. Motapothula and M. B. H. Breese, A study of small impact parameter ion channeling effects in thin crystals, Eur. Phys. J. B 91, 49 (2018)
Shedding new light on angle-selective Huygens’ metasurfaces (Vol. 49, No. 3)
Huygens’ metasurfaces form a class of ultra-thin optical devices which allow scientists to reshape the wavefront of an incident beam of light. Representatives of this class include highly efficient flat lenses, beam shapers, and holographic phase masks.
More specifically, such metasurfaces are composed of a carefully designed, two-dimensional arrangement of high-refractive-index dielectric nanoparticles, which show virtually no absorption losses and exhibit electric and magnetic dipole resonances known from Mie scattering. When these resonances are designed to overlap spectrally, the nanoparticles scatter almost all light in the forward-direction only, and thereby emulate the behavior of the forward-propagating elementary wavelets known from Huygens’ principle. The authors have investigated this effect in dependence on the incidence angle and polarization of incident plane waves for a metasurface composed of silicon nanocylinders. They showed that the resonance overlap can be designed to appear at an arbitrary incidence angle. Furthermore, since the metasurface blocks all light incident at angles other than the design angle, angle-selective functionalities may be implemented as well. These findings open interesting opportunities for the design of advanced wavefront-shaping devices and computer-generated holograms.
D. Arslan, K. E. Chong, A. E. Miroshnichenko, D.-Y. Choi, D. N. Neshev, T. Pertsch, Y. S. Kivshar and I. Staude, Angle-Selective All-Dielectric Huygens' Metasurfaces,
J. Phys. D: Appl. Phys. 50, 434002 (2017)
Six decades of cosmology (Vol. 49, No. 3)
The personal memories of Jayant Narlikar point to the need for restoring cosmology as the flagship of astronomy.
"Cosmologists are often wrong but never in doubt,” Russian physicist Lev Landau once said. In the early days, astronomers began by observing and modelling stars in different stages of evolution and comparing their findings with theoretical predictions. Stellar modelling uses well-tested physics, with concepts such as hydrostatic equilibrium, law of gravitation, thermodynamics, nuclear reactions etc. Yet in contrast, cosmology is based on a large number of untested physical assumptions, like nonbaryonic dark matter and dark energy whose physics has no proven link with the rest of physics. In a paper published recently, the author shares his personal reminiscences of the evolution of the subject of cosmology over six decades. He tells of the increase in our confidence in the standard model of cosmology to the extent that it has become a dogma. The German physicist Max Born said many years ago: "Modern cosmology has strayed from the sound empirical road to a wilderness where statements can be made without fear of observational check...”. The author feels that those comments apply very well to the present state of cosmology.
J. V.Narlikar , The evolution of modern cosmology as seen through a personal walk across six decades, Eur. Phys. J. H 43, 43 (2018)
Non-Stationary Noise with Memory in Josephson Junctions (Vol. 49, No. 3)
In addition to the non-dissipative supercurrent, Josephson junctions also possess a dissipative memristive current component, meaning that the instantaneous resistance of the junction depends on the history of the current. Devices that display this exotic behavior are currently under intense study due to possible applications ranging from fast, high-density, nonvolatile computer memories to neuromorphic computing. In a previous work, the authors suggested a novel device to isolate this current component and thus realize a superconducting memristor. In this work the manifestation of the memristive behaviour in the current noise is considered. The presence of memory renders this noise non-stationary. The authors theoretically characterize both the thermal noise and the 'dynamic'-noise arising across a biased junction, using a mixed time-frequency description. A way to detect this effect of the memristive behaviour on the current noise is also proposed, which should be feasible with current experimental tools.
F. Sheldon, S. Peotta and M. Di Ventra, Phase-dependent noise in Josephson junctions, Eur. Phys. J. Appl. Phys. 81, 10601 (2018)
Approximate quantum cloning: the new way of eavesdropping in quantum cryptography (Vol. 49, No. 3)
New approximate cloning method avoids the previous limitations of quantum cloning to enhance quantum computing and quantum cryptography leaks
Cloning of quantum states is used for eavesdropping in quantum cryptography. It also has applications in quantum computation based on quantum information distribution. Uncertainty at the quantum scale makes exact cloning of quantum states impossible. Yet, they may be copied in an approximate way—with a certain level of probability—using a method called probabilistic quantum cloning, or PQC. In a new study published recently, the authors demonstrate that partial PQC of a given quantum state secretly chosen from a certain set of states, which can be expressed as the superposition of the other states, is possible. This cloning operation is very important with regard to classical computing. It allows scientists to make many copies of the output of computations—which take the form of unitary operations. These can, in turn, be used as input and fed into various further processes. In quantum computing, for example, previous studies have shown that PQC can help to enhance performance compared to alternative methods. This means that when unitary operations generate some linearly-dependent states, partial PQC can be helpful.
P. Rui, W. Zhang, Y. Liao and Z. Zhang, Probabilistic quantum cloning of a subset of linearly dependent states, Eur. Phys. J. D 72, 26 (2018)
Rare events in “noisy” networks (Vol. 49, No. 3)
Bringing diseases to extinction and mitigating the effects of human-caused environmental changes which accelerate the rate of species extinction are issues of worldwide importance. Both phenomena are typically rare events, relying on the interplay between network topology, nonlinear dynamics, and random fluctuations from the environment and interactions. However, the prediction of such rare events in general stochastic networks was an unsolved problem, despite extensive work in network dynamics. Here we solve the problem of predicting rare events as large fluctuations from metastable states with a general theory that combines mean-field approximations, large-deviation techniques and network topology. A benefit of our approach is its flexibility in describing the effects of multiple sources of different continuous and discrete noise. Using our theory, we demonstrate that networks with both internal interaction noise and external parameter noise exhibit a cross-over where the familiar exponential scaling of rare-event times with the number of nodes in the network is lost, and parametric noise dominates.
J. Hindes and I. B. Schwartz, Rare events in networks with internal and external noise, EPL 120, 56004 (2017)
A happy marriage between critical phenomena and spintronics (Vol. 49, No. 3)
Spintronics is a technology that aims to use spin in information processing for practical application, whereas critical phenomena belong to an academic subject that deals with phase transition. These two seemingly different subfields meet at the interface between a magnetic insulator and a paramagnetic metal. The thermal spin injection from an insulating magnet into the adjacent heavy metal is referred to as spin Seebeck effect. Since its discovery in 2008, this phenomenon has attracted much attention as a simple and versatile means for generating spin current that is needed to drive the functionality of spintronic devices. The spin Seebeck effect has been investigated extensively over the last few years, but only a little is known about its behaviour near the magnetic phase transition.
Using a stochastic model established through the study of dynamic critical phenomena, the authors have investigated the behavior of the spin Seebeck effect near the Curie temperature Tc of a simple ferromagnet which is composed of a single sublattice such as EuO. They have clarified theoretically that the spin Seebeck signal scales with the magnetization, i.e., ~(T-Tc)1/2. Because no corresponding experiments have been reported so far, the theoretical prediction awaits experimental proof.
H. Adachi, Y. Yamamoto and M. Ichioka, Spin Seebeck effect in a simple ferromagnet near Tc: a Ginzburg–Landau approach, J. Phys. D: Appl. Phys. 51, 144001 (2018)