Articles in 2021

Very high energy electrons (VHEE) penetrate deeply in tissues and can provide an alternative to photon irradiation for tumour treatment. Using VHEE beams at CERN Linear Electron Accelerator for Research (CLEAR) focused into a water phantom, the authors demonstrate on-axis dose enhancement at a depth of 5–6 cm, proving that such beams can produce dose concentration to small volume elements, hence limiting the effect on adjacent healthy tissues if used for radiotherapy.

Turbulent flows have been the subject of intensive studies, but experimental investigations are lacking due to the need for high-frequency and high-resolution methods to probe small scale structure and time evolution. The authors report high repetition rate, high spatial resolution, particle image velocimetry measurements of a turbulent, circular jet flow, revealing that the turbulent jet measured is inhomogeneous and anisotropic and demonstrating that Taylor’s frozen turbulence hypothesis fails to generalize for inhomogeneous jet flows.

The lack of a clean charge neutral cleavage plane for the 122 family of iron-based superconductors has complicated surface-sensitive spectroscopy probes from revealing the intrinsic electronic properties of these materials. Here the authors introduce an effective surface dosing method that drastically improves the observed spectral quality, thus revealing unprecedented details of the superconducting gap anisotropy.

Graphene exhibits both extremely high electrical conductivity and electron mobility but an incomplete understanding of the underlying mechanisms so far limits potential applications in electrical devices. Here, the authors theoretically and experimentally investigate the role of charged impurities and optical phonons on the conductivity properties of graphene and establish a universal connection between the mobility and conductivity.

Bose-Einstein condensation was theoretically predicted almost 150 years ago but experimentally realized this century, reviving the interest in this striking quantum phenomenon. The authors present a system of strongly interacting bosons that have the ability to go from the quasi-condensation state of matter to a fully Bose-Einstein condensate, showing that this phase transition can be achieved by just tuning one parameter.

Understanding how social interactions between individuals shape the large-scale properties of social networks is key to understanding our society. Here, the authors revisit the Adjacent Possible paradigm to describe the evolution of social networks as a social space exploration process, presenting a simple model that reproduces several empirical features common to diverse real-world social networks.

Gravitational wave astronomy is on a path to increase the sensitivity and bandwidth of their detectors to afford the possibility to study a larger variety of sources and physical processes. The authors present solutions to enhance the sensitivity of a laser interferometric gravitational wave detector in the frequency band of 1-5 kHz using optomechanics-based white light signal recycling technologies, overcoming previous limitations of signal recycling.

Magnetic monopoles are predicted by grand unified theories but remain elusive as elementary particles. Here, extending electric-magnetic symmetry onto full quantum behavior, the authors demonstrate that magnetic monopoles emerge as excitations in condensed matter systems, where they can form a quantum Bose condensate manifesting as a superinsulating state dual to superconductivity, made of charge Cooper pair condensate.

In quantum physics, observables are generally believed to be Hermitian, but there are several examples of non-Hermitian systems possessing real positive eigenvalues, particularly among open systems. Here, the authors simulate the evolution of a non-Hermitian Hamiltonian on a superconducting quantum processor using a dilation procedure involving an ancillary qubit, and observe the parity–time (PT)-symmetry breaking phase transition at the exceptional points.

A general theory for dynamical processes in higher-order systems is still missing. Here, the authors provide a general mathematical framework based on linear stability analysis that allows to assess the stability of classes of processes on arbitrary hypergraphs.

While 3D printing applications range from aerospace manufacturing to the design of drug delivery systems, current technologies reaching the micro and nanoscale resolution are limited by the complexity and cost of their components. Here, the authors show that nanoscale cost-effective 3D printing can be achieved by using a gaming console optical drive pickup for 3D photopolymerization.

Optical computing holds promise for high-speed, low-energy information processing due to its large bandwidth and ability to multiplex signals. The authors propose a recurrent neural network implementation using reservoir computing architecture in an integrated photonic processor capable of performing ~10 tera multiplication–accumulation operations per second for each wavelength channel.

Understanding the mechanisms underlying collective motion in cells is central to understanding tissue development as well as the emergence of several pathologies. Here, the authors study the mesoscale turbulence of confluent cell monolayers through a combined experimental and numerical approach, finding that energetic statistics are independent of cell types and substrate stiffness.

Estimating the capacity of quantum channels is relevant to understand at which rate quantum information can be exchanged. Here, the authors introduce multi-level amplitude damping channels that generalize the qubit amplitude damping noise model, analyse their quantum and private capacities, and exactly derive the capacities of quantum channels that are not anti-degradable.

Antihydrogen atoms are a unique type of antimatter that can be used to probe small violations of fundamental laws of physics. The authors present experimental results obtained with the AEgIS project at CERN for the production of antihydrogen atoms (Hbar) via charge exchange with laser excited positronium that allow for precise timing of Hbar production.

Magnons are the quantized spin waves, which describe the collective magnetic excitations and the long-range magnetic order in a solid. Here, the authors describe how to engineer magnonic band structures at the interface and surface of ferromagnetic layered structures and how such magnonic states alter the transport properties.

While control theory for optimal navigation is relevant across scales, from aeronautics to targeted drug delivery, the role of thermal fluctuations and hydrodynamic interactions with interfaces, walls and obstacles at the microscale remains an open question. Here, the authors explore optimal microswimming in the presence of walls or obstacles, and study how hydrodynamic microswimmer-wall interactions impact on optimal microswimming strategies.

Cavity-enhanced spectroscopy is used to analyse light–matter interactions in fields such as ultracold chemistry and planetary science but measurement performance can be hampered by nonlinearities and long acquisition times. Here, the authors report a technique called cavity build up dispersion spectroscopy to measure dispersive frequency shifts demonstrating increased acquisition speeds and less susceptibility to detector nonlinearity.