Trapping nanoparticles with optical tweezers (Vol. 52, No. 1)

Trapping fluorescent particles with Arago spots

Optical tweezers are a rapidly growing technology, and have opened up a wide variety of research applications in recent years. The devices operate by trapping particles at the focal points of tightly focused laser beams, allowing researchers to manipulate the objects without any physical contact. So far, optical tweezers have been used to confine objects just micrometres across – yet there is now a growing desire to extend the technology to nanometre-scale particles. Janine Emile and Olivier Emile at the University of Rennes, France, demonstrate a novel tweezer design, which enabled them to trap fluorescent particles just 200 nanometres across for the first time.

O. Emile, J. Emile, Nanometre optical trap based on stimulated emission in evanescence of a totally reflected Arago spot, Eur. Phys. J. E 43, 68 (2020)

Detecting solar neutrinos with the Borexino experiment (Vol. 52, No. 1)

Distribution of best-fit results of 210Bi and CNO neutrinos interaction rates obtained fitting thousands of simulated datasets under different assumptions of 210Bi backgrounds.

Neutrinos produced by the CNO cycle within the core of the Sun are being hunted by the Borexino experiment so that we may learn more about this important nuclear process. A paper by the Borexino collaboration – including XueFeng Ding, Postdoc Associate of Physics at Princeton University, United States – documents the attempts of the Borexino experiment to measure low-energy neutrinos from the Sun’s carbon-nitrogen-oxygen (CNO) cycle for the first time.

M. Agostini et al. (BOREXINO collaboration), Sensitivity to neutrinos from the solar CNO cycle in Borexino, Eur. Phys. J. C 80, 1091 (2020)

Can quarantine do more than just “flatten the curve”? (Vol. 52, No. 1)

The fraction of susceptible (main figure) and infected individuals (inset) for a single-phase soft quarantine and a two-phase quarantine.

Our modeling of the epidemic shows that compared to a single-phase soft quarantine, a quarantine composed of a strict phase followed by a softer one results in a smaller overall number of infected individuals. This occurs if individuals with anomalously-many connections such as essential workers or store cashiers become immune before all others are allowed to come out of the strict quarantine. In this case, the most “socially connected” individuals, once recovered, act as efficient breaks in the network of disease transmission.

V. Nimmagadda, O. Kogan and E. Khain, Path-dependent course of epidemic: Are two phases of quarantine better than one?', EPL 132 (2020)

Automated symmetry adaption in nuclear many-body theory (Vol. 52, No. 1)

Symmetry reduction process of a prototypical many-body expression leading to an equivalent symmetry-reduced form. Recoupling coefficients arising from the AMC program are shown in red.

The extreme cost of solving the A-nucleon Schrödinger equation can be minimised by leveraging rotational symmetry and, thus, enable the computation of observables in heavy nuclei and/or with high precision.

The associated reduction process, which amounts to re-expressing the working equations in terms of rotationally-invariant objects, requires lengthy symbolic manipulations of elaborate algebraic identities.

For the first time, this involved process is automated by a powerful graph-theory-based tool, the AMC code, which condenses months of error-prone derivations into a simple computational task performed within seconds.

The AMC program tightens the gap for a full automation of the many-body workflow, thereby lowering the time required to build and test novel quantum many-body formalisms.

A. Tichai, R. Wirth, J. Ripoche and T. Duguet, Symmetry reduction of tensor networks in manybody theory, Eur. Phys. J. A 56, 272 (2020)

School on Energy (Vol. 52, No. 1)

Participants of the school at the Villa Monastero in Varenna, Lake Como, Italy

Since 2012, the European Physical Society and the Italian Physical Society jointly organise a biennal International School on Energy as part the training of young scientists working in the energy sector or intending to do so. The proceedings of the 5th Course with the title ‘Energy: where we stand and where we go’ are published in the EPJ Web of Conferences. Editors of the proceedings are L. Cifarelli and F. Wagner.

EPJ/WoS, Volume 246 (2020)