Table of contents

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single- and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that nature cannot be local, that objective randomness exists and about the emergence of a classical world. It is suggestive that information plays a fundamental role also in the foundations of quantum physics.

A new segmented particle detector, SPIDER, has been designed to be used as an ancillary device with the GALILEO γ-ray spectrometer, as well as with other multi-detector γ-ray arrays that will be available at LNL in the future (e.g. AGATA). To commission the SPIDER-GALILEO experimental setup, a multi-step Coulomb excitation experiment was carried out with a 240 MeV beam of ⁶⁶Zn produced by the Tandem-XTU accelerator at INFN Laboratori Nazionali di Legnaro. The measured particle and γ-ray spectra are compared with the results of detailed GEANT4 simulations which used the Coulomb excitation cross sections, estimated with the computer code GOSIA, as an input. The preliminary results indicate that precise transition probabilities will be obtained which are essential for solving discrepancies reported in the literature for this nucleus.

With the advent of γ-ray tracking detector arrays, it should be possible to measure entry distributions and the quasi-continuum of γ rays with better accuracy than was possible with the previous generation of escape—suppressed detector arrays. However, the techniques for doing so may represent more of a challenge for these new tracking arrays. Here, the techniques developed recently are being presented.

The formalism of an equation of motion phonon method is briefly outlined. In even–even nuclei, the method derives equations of motion which generate an orthonormal basis of correlated n-phonon states (n = 0, 1, 2, ...), built of constituent Tamm–Dancoff phonons, and, then, solves the nuclear eigenvalue problem in such a multiphonon basis. In odd nuclei, analogous equations yield a basis of correlated orthonormal multiphonon particle–core states to be used for the solution of the full eigenvalue equations. The formalism does not rely on approximations, but lends itself naturally to simplifying assumptions. As illustrated here, the method has been implemented numerically for studying the electric dipole response in the heavy neutron rich ²⁰⁸Pb and ¹³²Sn and in the odd ¹⁷O and ¹⁷F. Self-consistent calculations, using a chiral inspired Hamiltonian, have confirmed the important role of the multiphonon states in enhancing the fragmentation of the strength in the giant and pygmy resonance regions consistently with the experimental data.

Isomeric studies in neutron-rich nuclei are a powerful tool for exploring structure at the nuclear extremes. In this paper we discuss the systematic features of the excitation energies and transition probabilities of Sn isotopes in the region N = 50–82 and present their basic understanding in terms of generalized seniority. We further use generalized seniority as a probe to explore the neutron-rich ${6}^{+}$ seniority isomers in ^134–138Sn, and to validate the neutron single-particle energies beyond N = 82. We show that these isomers behave as generalized seniority isomers, where the so-called anomalous ${\rm{B}}(E2)$ behavior of the ${6}^{+}$ isomer in ¹³⁶Sn may be naturally explained. We support these results by shell model calculations, where the latest neutron single-particle energies of the N = 82–126 region have been used, and the i_13/2 neutron single-particle energy has been suitably modified in the renormalized charge-dependent Bonn interaction. This entails a possible new subshell closure at N = 112 due to the suggested higher location of the i_13/2 neutron orbital, also consistent with the choice of orbitals in the generalized seniority scheme. However, a small reduction in the f_7/2 two-body matrix elements is still required in the shell model calculations to consistently reproduce the experimental level energies as well as the transition probabilities in ^134–138Sn isotopes.

The semiclassical origins of the enhancement of shell effects in exotic-shape mean-field potentials are investigated by focusing attention on the roles of the local symmetries associated with the periodic-orbit bifurcations. The deformed shell structures for four types of pure octupole shapes in the nuclear mean-field model having a realistic radial dependence are analyzed. Remarkable shell effects are shown for a large Y₃₂ deformation having tetrahedral symmetry. Much stronger shell effects found in the shape parametrization smoothly connecting the sphere and the tetrahedron are investigated from the view-point of the classical–quantum correspondence. The local dynamical symmetries associated with the bridge orbit bifurcations are shown to have significant roles in the emergence of exotic deformed shell structures for certain combinations of the surface diffuseness and the tetrahedral deformation parameters.

Previous research into three-dimensional numerical simulation of self-similar mixing due to Rayleigh–Taylor instability is summarized. A range of numerical approaches has been used: direct numerical simulation, implicit large eddy simulation and large eddy simulation with an explicit model for sub-grid-scale dissipation. However, few papers have made direct comparisons between the various approaches. The main purpose of the current paper is to give comparisons of direct numerical simulations and implicit large eddy simulations using the same computational framework. Results are shown for four test cases: (i) single-mode Rayleigh–Taylor instability, (ii) self-similar Rayleigh–Taylor mixing, (iii) three-layer mixing and (iv) a tilted-rig Rayleigh–Taylor experiment. It is found that both approaches give similar results for the high-Reynolds number behavior. Direct numerical simulation is needed to assess the influence of finite Reynolds number.

We present a detailed investigation of the transition properties for He-like Al embedded in hot and dense plasma environments. The correlation effect between the bound electrons is treated with the configuration interaction method. Plasma screening on the nucleus is described using the self-consistent-field ion sphere model. Transition energies, transition probabilities and weighted oscillator strengths decrease quickly with the increase of free electron densities, but increase slightly with the electron temperature, and approach those of the uniform electron density ion sphere model at a given average free electron density. The results reported in this work are useful for plasma diagnostics.

The possibility of using a rotating magnetic field (RMF) in a plasma centrifuge (PC), with axial circulation to multiply the radial separation effect in an axial direction, is considered. For the first time, a traveling magnetic field (TMF) is proposed to drive an axial circulation flow in a PC. The longitudinal separation effect is calculated for a notional model, using specified operational parameters and the properties of a plasma, comprising an isotopic mixture of ²⁰Ne–²²Ne and generated by a high frequency discharge. The optimal intensity of a circulation flow, in which the longitudinal separation effect reaches its maximum value, is studied. The optimal parameters of the RMF and TMF for effective separation, as well as the centrifuge performance, are calculated.

The electrorheological (ER) effect is known as the enhancement of the apparent viscosity upon application of an external electric field applied perpendicular to the flow direction. Suspensions of polarizable particles in non-conducting solvents are the most studied ER fluids. The increase in viscosity observed in the suspensions is due to the formation of columns that align with the electric field. This work presents the ER behavior of suspensions, in silicone oil, of camphorsulfonic acid (CSA) doped polyaniline (PANI) nanofibers. The ER properties of the suspensions were investigated with a rotational rheometer, to which an ER cell was coupled, in steady shear, and electrical field strengths up to 2 kV mm⁻¹. The effects of the electric field strength, content of nanostructures and viscosity of the continuum phase, in the shear viscosity and yield stress, were investigated at room temperature. As expected, the ER effect increases with the increase of the electric field as well as with the increase of content of nanofibers and it decreases with the increase of the oil viscosity. The suspensions present giant ER effects (higher than 2 orders of magnitude increase in viscosity for low shear rates and high electric fields), showing their potential application as ER smart materials.