## EPJ D Highlight - Slowing light in an optical cavity with mechanical resonators and mirrors

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- Published on 15 October 2020

Theoretical physicists Kamran Ullah and Hameed Ullah have shown how a position-dependent mass optomechanical system involving a cavity between two mirrors, one attached to a resonator, can enhance induced transparency and reduce the speed of light.

We are all taught at high school that the speed of light through a vacuum is about 300000 km/s, which means that a beam from Earth takes about 2.5 seconds to reach the Moon. It naturally moves more slowly through transparent objects, however, and scientists have found ways to slow it dramatically. Optomechanics, or the interaction of electromagnetic radiation with mechanical systems, is a relatively new and effective way of approaching this. Theoretical physicists Kamran Ullah from Quaid-i-Azam University, Islamabad, Pakistan and Hameed Ullah from the Institute of Physics, Porto Alegre, Brazil have now demonstrated how light is slowed in a position-based mass optomechanical system. This work has been published in *EPJ D*.

## EPJ D Topical review - Crystal-based intensive gamma-ray light sources

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- Published on 06 October 2020

In a Topical review just published in EPJD, A.V. Korol and A.V. Solov'yov (MBN Research Center, Germany) discuss possibilities for designing and practical realization of novel intensive gamma-ray Crystal-based LSs (CLS) operating at photon energies from 102 keV and above that can be constructed exposing oriented crystals to beams of ultrarelativistic particles. CLSs can generate radiation in the photon energy range where the technologies based on the fields of permanent magnets become inefficient or incapable.

## EPJ D Highlight - Avoiding environmental losses in quantum information systems

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- Published on 28 September 2020

Through new techniques for generating ‘exceptional points’ in quantum information systems, researchers have minimised the transitions through which they lose information to their surrounding environments.

Recently, researchers have begun to exploit the effects of quantum mechanics to process information in some fascinating new ways. One of the main challenges faced by these efforts is that systems can easily lose their quantum information as they interact with particles in their surrounding environments. To understand this behaviour, researchers in the past have used advanced models to observe how systems can spontaneously evolve into different states over time – losing their quantum information in the process. Through new research published in *EPJ D*, M. Reboiro and colleagues at the University of La Plata in Argentina have discovered how robust initial states can be prepared in quantum information systems, avoiding any unwanted transitions extensive time periods.

## EPJ D Colloquium - Simulating lattice gauge theories within quantum technologies

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- Published on 17 August 2020

## EPJ D Highlight - Measuring electron emission from irradiated biomolecules

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- Published on 06 August 2020

OrigiA new experiment has characterised the properties of the electrons emitted when a key constituent of DNA is bombarded with high-velocity ions.

When fast-moving ions cross paths with large biomolecules, the resulting collisions produce many low-energy electrons which can go on to ionise the molecules even further. To fully understand how biological structures are affected by this radiation, it is important for physicists to measure how electrons are scattered during collisions. So far, however, researchers’ understanding of the process has remained limited. In new research published in *EPJ D*, researchers in India and Argentina, led by Lokesh Tribedi at the Tata Institute of Fundamental Research, have successfully determined the characteristics of electron emission when high-velocity ions collide with adenine – one of the four key nucleobases of DNA.

## EPJ D Topical review - Wigner scattering theory for systems held together by Coulombic forces

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- Published on 11 June 2020

Originally developed and formulated for nuclear scattering, Wigner’s theory is extremely general, with application in many branches of physics. Atomic Physics often makes use of an apparently separate formalism (MQDT) which is in fact a specialisation of Wigner’s theory. In a new Topical Review article published in EPJD, Jean-Patrick Connerade (Imperial College London, UK and and European Academy EASAL, France) discusses the relevance of Wigner Scattering theory and in particular its K-matrix formulation for all systems held together by coulombic forces, including not only atoms and molecules but also clusters.

## EPJ D Highlight - Stresses and flows in ultra-cold superfluids

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- Published on 08 May 2020

Mathematical modelling of superfluids, which exhibit quantum mechanical properties at a macroscopic scale, shows that they become deformed when flowing around impurities.

Superfluids, which form only at temperatures close to absolute zero, have unique and in some ways bizarre mechanical properties, Yvan Buggy of the Institute of Photonics and Quantum Sciences at Heriot-Watt University in Edinburgh, Scotland, and his co-workers have developed a new quantum mechanical model of some of these properties, which illustrates how these fluids will deform as they flow around impurities. This work is published in the journal *EPJ D*.

## EPJ D Topical review - Recent total cross section measurements in electron scattering from molecules

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- Published on 05 May 2020

Accurate new experimental data on electron interactions with matter are necessary for the understanding of a wide variety of natural and technological processes occurring in complex environments. Knowledge of the efficiency of electron interactions with biomolecules is crucial for the description and modeling of ionizing radiation damage to living cells and biomolecules radiolysis. Accurate experimental data concerning electron interactions are also important for the description of many phenomena occurring in plasma physics and gaseous electronics, including modeling of processes in cometary and planetary atmospheres.

## EPJ D Highlight - Questionable stability of dissipative topological models for classical and quantum systems

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- Published on 15 April 2020

Physicists Rebekka Koch and Jan Carl Budich make important contributions to understanding dissipative topological systems by studying the spectral instabilities that occur in the mathematical description and their effect on experimental setups in a new paper in EPJ D.

Energy conservation lies at the core of every physical theory. Effective mathematical models however can feature energy gain and/or loss and thus break the energy conservation law by only capturing the physics of a subsystem. As a result, the Hamiltonian, the function that describes the system's energy, loses an important mathematical property: it is no longer Hermitian. Such non-Hermitian Hamiltonians have successfully described experimental setups for both classical problems – in e.g. some optical systems and electrical circuits - and quantum ones, in modelling the motion of electrons in crystalline solids. In a new paper in *EPJ D*, physicists Rebekka Koch from the University of Amsterdam in the Netherlands and Jan Carl Budich from Technische Universität Dresden, in Germany, describe how these functions provide new insights into behaviour at the edges of topological materials.

## EPJ D Highlight - Looking for dark matter

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- Published on 08 April 2020

A new paper in EPJ D, ‘Constraining domain wall dark matter with a network of superconducting gravimeters and LIGO’, suggests two novel methods of searching for dark matter by measuring tiny perturbations in fundamental constants.

Dark matter, which cannot be physically observed with ordinary instruments, is thought to account for well over half the matter in the Universe, but its properties are still mysterious. One commonly held theory states that it exists as ‘clumps’ of extremely light particles. When the earth passes through such a clump, the fundamental properties of matter are altered in ways that can be detected if instruments are sensitive enough. Physicists Rees McNally and Tanya Zelevinsky from Columbia University, New York, USA, have now published a paper in *EPJ D* proposing two new methods of looking for such perturbations and, thus, dark matter. This paper is part of the EPJD Topical Issue on Quantum Technologies for Gravitational Physics which is still open to submissions.