Statistical uncertainty in line shift and width interpretation (Vol. 43 No. 6)

I.H. Hutchinson, ‘Statistical uncertainty in line shift and width interpretation’, Eur. Phys. J. Plus, 127, 81 (2012)
[Abstract]

Stimulating resonance with two very different forces (Vol. 51, No. 3)

In some specialised oscillators, two driving forces with significantly different frequencies can work together to make the whole system resonate.

“Nonlinear’ systems can display dramatic responses when the forces which cause them to vibrate are changed. Some of these systems are sensitive to changes in the parameters which define their driving forces, and can be well described using mathematical equations. In this work, it is shown in detail for the first time that some ‘parametric’ oscillators can be made to resonate when tuned by a high driving frequency to match a separate, far lower frequency.

S Roy, D Das, D Banerjee, Nonlinear Response of a Parametric Bistable Oscillator with Multiple Excitations, Eur. Phys. J. B 93, 12 (2020)
[Abstract]

Strong field ionization yields in linear and asymmetric top molecules (Vol. 43 No. 2)

Total ionization yield of field-free aligned OCS (blue triangles, <cos²θ₂d> = 0.84) and adiabatically aligned OCS molecules (red squares, <cos²θ₂d> = 0.90) as a function of the angle between the polarization axes of the alignment and probe pulses (dashed curves are included to guide the eye). The ionization yield is modeled using standard MO-ADK (solid magenta) and Stark-shift-modified MO-ADK (solid green). Both calculations assume <cos²θ₂d> = 0.90.

Orientation-dependent ionization yields from strong-field ionization of fixed-in-space linear and asymmetric top molecules
J. L. Hansen, L. Holmegaard, J. H. Nielsen, H. Stapelfeldt, D. Dimitrovski and L. B. Madsen, J. Phys. B: At. Mol. Opt. Phys. 45, 015101 (2012)
[Abstract]

Structure-function clustering in multiplex brain networks (Vol. 48 No. 1)

A key question in neuroscience is to explain how the brain’s rich repertoire arises within relatively static anatomical networks: understanding the relationships between this structure and the ‘functional’ connections (inferred from the synchronisation of activity between brain areas) it supports has the potential to address this. We employ a multiplex approach, in which anatomical and functional networks are analysed simultaneously. In particular, we consider a network describing the structural connectivity of the Macaque cortex, and a functional network derived from simulated neural activity. By comparison with single-layer approaches, our results provide the first demonstration that multiplex analyses of structure-function networks are better placed to capture emergent features of neural systems. Moreover, we propose a novel multiplex structure-function clustering measure that allows us to highlight the dependence of functional structure on the particular neural dynamical regime, and to characterise the emergent disparity between functional and anatomical networks. This divergence is fundamental to higher brain function - our new measure, that quantifies precisely this disparity, and our multiplex approach more generally, represents a new avenue towards understanding structure-function relationships at a more fundamental level.

J. J. Crofts, M. Forrester and R. D. O’Dea, Structure-function clustering in multiplex brain networks, EPL 116, 18003 (2016)
[Abstract]

Studying emotions causing opinions to change (Vol. 44 No. 5)

Example of evolution of agent opinions.

P. Sobkowicz, ‘Minority persistence in agent based model using information and emotional arousal as control variables’, Eur. Phys. J. B, (2013)
[Abstract]

Subrecoil cavity cooling towards degeneration (Vol. 45 No.2)

Single-particle momentum distribution for bosons in a ring cavity. The initially broad distribution is cavity-cooled to |p| = 0, ±1hk momentum states.

Cavity assisted cooling has become a valuable tool to implement cavity-QED with ultra cold quantum gases, trapped ions and optomechanical elements. Injecting a red-detuned laser extracts kinetic energy from the particles to create cavity photons, which leak out of the resonator, carrying away energy and effectively cooling the system. In contrast to conventional laser cooling, this method works without resonant excitation and spontaneous emission, eliminating photon re-absorption and making it applicable to a wide class of polarisable particles with final temperatures only limited by the cavity line-width.

We present a detailed numerical analysis of the cooling dynamics involving a cavity with energy uncertainty below the recoil energy. Motivated by a recent Hamburg experiment demonstrating targeted cooling on the subrecoil scale, we embrace a tailored sequence of laser pulses transferring the particles from a thermal state towards the ground state reaching subrecoil kinetic energies. The few particle simulations give encouraging prospects to implement condensation of a quantum gas via cavity cooling and exhibit genuine quantum correlations distinguishing fermions and bosons.

A broad momentum distribution is cooled to generate a large ground state population. Each step of a laser pulse sequence with optimized detunings transfers specific momentum states irreversibly towards lower momenta.

R. M. Sandner, W. Niedenzu and H. Ritsch, “Subrecoil cavity towards degeneration: a numerical study”, EPL, 104, 43001 (2013)
[Abstract]

Subtracted dispersion relation estimate of two-photon exchange (Vol. 46 No. 3)

Elastic electron-proton scatterings (with one-photon exchange) have always provided fundamental information on general properties of the proton. Recently, two experimental approaches, with and without polarized protons, gave strikingly different results for the electric over magnetic proton form factor ratio. Similarly, a mysterious discrepancy (“the proton radius puzzle”) has been observed in the measurement of the proton charge radius in different experiments, one of which is electron-proton scattering. Two-photon exchange (TPE) contributions have been proposed as a plausible solution to resolve the puzzles, but their estimates have strong model dependences. A quantitative understanding of TPE effects, based on general principles and avoiding model dependences, is necessary. A subtracted dispersion relation formalism for the TPE has been developed and tested. Its relative effect δ2γ on the elastic cross section is in the 1-2 % range for a low value of the momentum transfer Q2 as function of the kinematic parameter ε, ranging between ε = 0 (backward scattering) and ε = 1 (forward scattering). Summarizing, the paper studies in a theoretical framework which minimizes the model dependence, the TPE contributions to electron-proton scattering, a precision experiment crucial for measuring the most fundamental proton properties.

O. Tomalak and M. Vanderhaeghen, Subtracted dispersion relation formalism for the two-photon exchange correction to elastic electron-proton scattering: Comparison with data”, Eur. Phys. J. A 51, 24 (2015)
[Abstract]

Super-focusing of light with a plasmonic super lens (Vol. 46 No. 1)

The diffraction barrier, which states that the FWHM of a focal spot cannot be lower than λ/2, has hampered investigators from visualizing nanoscale processes. Since the discovery of Extraordinary Optical Transmission and Surface Plasmon Polaritons, hope was renewed in building devices that can potentially break the formidable diffraction barrier. However, they were either unsuccessful or too complicated. This imposed the question: can these devices be made simple enough to be translated into the real world?

The authors, working on a novel design of a plasmonic super lens, show that the answer to this question is “Yes”. In their contribution, they have proposed a plasmonic super lens that was shown to reach a FWHM of λ/3 consistently at various wavelengths ranging from the visible to the ultraviolet. The super lens also acts as a super-antenna that is capable of beaming the light in a small pencil beam with subwavelength width over a long distance allowing it to be used as an optical nano-tweezer.

M. El Maklizi, M. Hendawy and M. A. Swillam, “Super-focusing of visible and UV light using a meta surface”, J. Opt. 16, 105007 (2014)
[Abstract]

Superconducting strip: an ultra-low-voltage sensor? (Vol. 43 No. 4)

Moving vortices inside the weak conducting links carved into a current-carrying superconducting strip.

Dynamic and static phases of vortices under an applied drive in a superconducting stripe with an array of weak links
G.R. Berdiyorov, A.R. de C. Romaguera, M.V. Milosevic, M.M. Doria, L. Covaci and F.M. Peeters, Eur. Phys. J. B, 85, 130 (2012)
[Abstract]

Superconductivity and magnetic order in ErPdBi (Vol. 45 No. 1)

Superconducting (SC) and magnetic (AFM) phase diagram of ErPdBi. Inset: Half-Heusler crystal structure.

Half-Heusler compounds attract ample attention because of their flexible electronic structure. A new electronic state in this respect is the topological insulator, where the interior of the material is insulating, while the surface states are conducting. Surprisingly some of the topological half-Heusler compounds become superconducting at low temperatures. Topological superconductors are predicted to have a fully gapped unconventional pairing state in the interior, while the non-trivial topology gives rise to Majorana fermion states at the edge of the sample. The further interplay with magnetic order may lead to exotic superconducting phases.

In the paper the discovery is reported of a new candidate for topological superconductivity: ErPdBi. Magnetic and transport measurements demonstrate superconductivity at Tc = 1.22 K, and, moreover, magnetic order at TN= 1.06 K. Since TN ≈ Tc the interaction of superconductivity and magnetic order is expected to give rise to a complex ground state. Electronic structure calculations reveal a topologically non-trivial band inversion. Accordingly, ErPdBi is advocated as a novel, unique platform to study the interplay of topological states, superconductivity and magnetic order.

Y. Pan, A.M. Nikitin, T.V. Bay, Y.K. Huang, C. Paulsen, B.H. Yan and A. de Visser, "Superconductivity in the noncentrosymmetric half-Heusler compound ErPdBi", EPL, 104, 27001 (2013).
[Abstract]

Superconductivity found in BaPd2As2 single crystal (Vol. 47 No. 2)

In this work the single crystal of ThCr₂Si₂-type BaPd₂As₂ was successfully prepared by a self-flux growth method. The crystal structure was characterized by powder X-ray diffraction method, with the space group I4/mmm and lattice parameters a = 4.489(2) Å, c = 10.322(3) Å. From the characterizations of low temperature electrical resistivity, magnetic susceptibility and specific heat measurements, bulk superconductivity was clearly revealed in this compound, although it was not found in other structural types of BaPd2As2. The superconducting onset Tc (critical temperature) is 3.85 K and the zero resistivity happens at 3.80 K. Surprisingly, this Tc is much higher than those of all other isostructural Pd-based superconductors, such as CaPd₂As₂ (Tc = 1.27 K) and SrPd₂As₂ (Tc = 0.92 K). The reason that leads to a higher Tc in this compound deserves more detailed studies to understand the underlying mechanism.

Q. Guo, J. Yu1, B.-B. Ruan, D.-Y. Chen, X.-C. Wang, Q.-G. Mu, B.-J. Pan, G.-F. Chen and Z.-A. Ren, Superconductivity at 3.85 K in BaPd₂As₂ with the ThCr₂Si₂-type structure, EPL 113, 17002 (2016)
[Abstract]

Supersonic phenomena, the key to extremely low heat loss nano-electronics (Vol. 48 No. 1)

Supersonic solitary waves in nano-electronics crystals show potentials for electric charge or matter transport and energy storage with extremely low heat dissipation

Freak waves, as well as other less striking localised excitations, occur in nature at every scale. The current theory and models of such waves can be applied to physics and, among others, to oceanography, nonlinear optics and lasers, acoustics, plasmas, cosmological relativity and neuro-dynamics. However, they could also play a significant role at the quantum scale in nano-electronics. In a recent study, the authors performed computer simulations to compare two types of localised excitations in nano-electronics. Their findings, published in a recent study, confirm that such localised excitations are natural candidates for energy storage and transport. These, in turn, could lead to applications such as transistors with extremely low heat dissipation not using silicon.

M. G. Velarde, A. P. Chetverikov, W. Ebeling, S. V. Dmitriev and V. D. Lakhno, From solitons to discrete breathers, Eur. Phys. J. B 89, 233 (2016)
[Abstract]

Supersymmetry unveiled in periodic optical media (Vol. 46 No. 3)

Supersymmetry (SUSY) was conjectured in quantum field theory as a means to unify bosons and fermions. While SUSY would be helpful in solving paradoxes such as the cosmological constant problem, its evidence in particle physics remains elusive. However, SUSY can be applied to other areas of physics, ranging from quantum mechanics to optics.

Supersymmetric optics is a recent and promising research field. It enables to synthesize dielectric media with target scattering properties and with less stringent material requirements than e.g. metamaterials synthesized by transformation optics. SUSY optical structures can realize efficient mode conversion, spatial multiplexing, transparent interfaces and optical intersections.

In this work, the author has now disclosed the SUSY property of periodic optical media. SUSY in grating structures can find important applications to the synthesis of Bragg filters and distributed-feedback optical cavities. For example, the author describes how multiple SUSY can be used to design frequency comb transmission filters (see Figure).

Optical SUSY in periodic media is a powerful design tool that can be extended to include gain and loss, i.e. distributed feedback lasers, as well as optical media with parity-time (PT) symmetry.

S. Longhi,, Supersymmetric Bragg gratings, J. Opt. 17, 045803 (2015)
[Abstract]

Suppression of resonant two-photon ionization rate by Rabi oscillation (Vol. 42, No. 3)

Correlation between rabi oscillations and the time-dependence of the ionization probability for the resonant two-photon ionization of Ar+: (a) envelop of the laser field, (b) and (c) the square normof the probability amplitudes of the ground g state (blue) and of the intermediate i state (red) for aweak and a strong field case. The time-dependent ionization probability i.P. (green), is suppressed during the second half cycle of the rabi oscillations for the strong field case (c) due to the decrease in the probability amplitude of the intermediate state i.

Three-photon double ionization of Ar studied by photoelectron spectroscopy using extreme ultraviolet free-electron laser:Manifestation of resonance states of intermediate Ar⁺ ion
N. Miyauchi et al., J. Phys. B: At.Mol. Opt. Phys. 44, 07100 (2011)
[Abstract]

Surprising neutrino decoherence inside supernovae (Vol. 47 No. 5-6)

Theory to explain collective effects of neutrinos inside supernovae strengthened

Neutrinos are elementary particles known for displaying weak interactions. As a result, neutrinos passing each other in the same place hardly notice one another. Yet, neutrinos inside a supernova collectively behave differently because of their extremely high density. A new study reveals that neutrinos produced in the core of a supernova are highly localised compared to neutrinos from all other known sources. This result stems from a fresh estimate for an entity characterising these neutrinos, known as wave packets, which provide information on both their position and their momentum. These findings have just been published by the authors. The study suggests that the wave packet size is irrelevant in simpler cases. This means that the standard theory for explaining neutrino behaviour, which does not rely on wavepackets, now enjoys a more sound theoretical foundation.

J. Kersten and A. Yu. Smirnov, Decoherence and oscillations of supernova neutrinos, Eur. Phys. J. C 76, 339 (2016)
[Abstract]