Quantum physics in space

Belenchia A., Carlesso M., Bayraktar Ö., Dequal D., Derkach I., Gasbarri G., Herr W., Li Y.L., Rademacher M., Sidhu J., Oi D.K.L., Seidel S.T., Kaltenbaek R., Marquardt C., Ulbricht H., Usenko V.C., Wörner L., Xuereb A., Paternostro M., Advances in quantum technologies are giving rise to a revolution in the way fundamental physics questions are explored at the empirical level. At the same time, they are the seeds for future disruptive technological applications of quantum physics. Remarkably, a space-based environment may open many new avenues for exploring and employing quantum physics and technologies. Recently, space missions employing quantum technologies for fundamental or applied studies have been proposed and implemented with stunning results. The combination of quantum physics and its space application is the focus of this review: we cover both the fundamental scientific questions that can be tackled with quantum technologies in space and the possible implementation of these technologies for a variety of academic and commercial purposes.

Localization in the Discrete Non-linear Schrödinger Equation and Geometric Properties of the Microcanonical Surface

Arezzo C., Balducci F., Piergallini R., It is well known that, if the initial conditions have sufficiently high energy density, the dynamics of the classical Discrete Non-Linear Schrödinger Equation (DNLSE) on a lattice shows a form of breaking of ergodicity, with a finite fraction of the total charge accumulating on a few sites and residing there for times that diverge quickly in the thermodynamic limit. In this paper we show that this kind of localization can be attributed to some geometric properties of the microcanonical potential energy surface, and that it can be associated to a phase transition in the lowest eigenvalue of the Laplacian on said surface. We also show that the approximation of considering the phase space motion on the potential energy surface only, with effective decoupling of the potential and kinetic partition functions, is justified in the large connectivity limit, or fully connected model. In this model we further observe a synchronization transition, with a synchronized phase at low temperatures.

Reformulation of gauge theories in terms of gauge invariant fields

Fontana P., Pinto Barros J.C., We present a reformulation of gauge theories in terms of gauge invariant fields. Focusing on abelian theories, we show that the gauge and matter covariant fields can be recombined to introduce new gauge invariant degrees of freedom. Starting from the (1+1) dimensional case on the lattice, with both periodic and open boundary conditions, we then generalize to higher dimensions and to the continuum limit. To show explicit and physically relevant examples of the reformulation, we apply it to the Hamiltonian of a single particle in a (static) magnetic field, to pure abelian lattice gauge theories, to the Lagrangian of quantum electrodynamics in (3+1) dimensions and to the Hamiltonian of the 2d and the 3d Hofstadter model. In the latter, we show that the particular construction used to eliminate the gauge covariant fields enters the definition of the magnetic Brillouin zone. Finally, we briefly comment on relevance of the presented reformulation to the study of interacting gauge theories.

Theory of superlocalized magnetic nanoparticle hyperthermia: Rotating versus oscillating fields

Iszály Z., Márián I.G., Szabó I.A., The main idea of magnetic hyperthermia is to increase locally the temperature of the human body by means of injected superparamagnetic nanoparticles. They absorb energy from a time-dependent external magnetic field and transfer it into their environment. In the so-called superlocalization, the combination of an applied oscillating and a static magnetic field gradient provides even more focused heating since for large enough static field the dissipation is considerably reduced. Similar effect was found in the deterministic study of the rotating field combined with a static field gradient. Here we study theoretically the influence of thermal effects on superlocalization and on heating efficiency. We demonstrate that when time-dependent steady state motions of the magnetization vector are present in the zero temperature limit, then deterministic and stochastic results are very similar to each other. We also show that when steady state motions are absent, the superlocalization is severely reduced by thermal effects. Our most important finding is that in the low frequency range (ω→0) suitable for hyperthermia, the oscillating applied field is shown to result in two times larger intrinsic loss power and specific absorption rate then the rotating one with identical superlocalization ability which has importance in technical realization.