We present an experimental and theoretical investigation of the spectroscopy of dilute alkali atoms in a solid matrix of inert gases at cryogenic temperatures, specifically Rubidium atoms in a solid Argon or Neon matrix, and related aspects of the interaction energies between the alkali atoms and the atoms of the solid matrix. The system considered is relevant for matrix isolation spectroscopy, and it is at the basis of a recently proposed detector of cosmological axions, exploiting magnetic-type transitions between Zeeman sublevels of alkali atoms in a magnetic field, tuned to the axion mass, assumed in the meV range. Axions are one of the supposed constituents of the dark matter (DM) of the Universe. This kind of spectroscopy could be also relevant for the experimental search of new physics beyond the Standard Model, in particular the search of violations of time-reversal or parity-charge-conjugation (CP) symmetry. In order to efficiently resolve the axion-induced transition in alkali-doped solid matrices, it is necessary to reduce as much as possible the spectral linewidth of the electronic transitions involved. The theoretical investigation presented in this paper aims to estimate the order of magnitude of the inhomogeneous contribution to the linewidth due to the alkali–matrix interactions (Coulomb/exchange and dispersion), and to compare the theoretical results with our experimental measurements of spectra of dilute Rubidium atoms in Argon and Neon solid matrix. The comparison of the expected or measured spectral linewidths will be important for selecting the most appropriate combination of alkali atoms and matrix inert elements to be used in the proposed axion detection scheme. It is finally suggested that dilute Lithium atoms diffused in a cold parahydrogen solid matrix could be, overall, a good system upon which the proposed detector could be based.

We consider the cooperative spontaneous emission of a system of two identical atoms interacting with the electromagnetic field in the vacuum state and in the presence of an oscillating mirror. We assume that the two atoms, one in the ground state and the other in the excited state, are prepared in a correlated (symmetric or antisymmetric) Bell-type state. We also suppose that the perfectly reflecting plate oscillates adiabatically, with the field modes satisfying the boundary conditions at the mirror surface at any given instant, so that the time dependence of the interaction Hamiltonian is entirely enclosed in the instantaneous atom-wall distance. Using time-dependent perturbation theory, we investigate the spectrum of the radiation emitted by the two-atom system, showing how the oscillation of the boundary modifies the features of the emitted spectrum, which exhibits two lateral peaks not present in the case of a static boundary. We also evaluate the transition rate to the collective ground state of the two-atom system in both cases of the superradiant (symmetric) and subradiant (antisymmetric) state. We show that it is modulated in time and that the presence of the oscillating mirror can enhance or inhibit the decay rate compared to the case of atoms in vacuum space or near a static boundary. Our results thus suggest that a dynamical (i.e., time-modulated) environment can offer further possibilities to control and manipulate radiative processes of atoms or molecules nearby, such as the cooperative decay, and strongly indicate a similar possibility for other radiative processes, for example, the resonance interaction and the energy transfer between atoms or molecules.

We consider the energy transfer process between two identical atoms placed inside a perfectly conducting cylindrical waveguide. We first introduce a general analytical expression of the energy transfer amplitude in terms of the electromagnetic Green's tensor; we then evaluate it in the case of a cylindrical waveguide made of a perfect conductor, for which analytical forms of the Green's tensor exist. We numerically analyse the energy transfer amplitude when the radius of the waveguide is such that the transition frequency of both atoms is below the lower cutoff frequency of the waveguide, so that the resonant photon exchange is strongly suppressed. We consider both cases of atomic dipoles parallel and orthogonal to the axis of the guide. In both cases, we find that the energy transfer is modified by the presence of the waveguide. In the near zone, that is when the atomic separation is smaller than the atomic transition wavelength, the change, with respect to the free-space case, is small for axial dipoles, while it is larger for radial dipoles; it grows when the intermediate region between near and far zone is approached. In the far zone, we find that the energy transfer amplitude is strongly suppressed by the waveguide, becoming virtually zero. A physical interpretation of these results is discussed. Finally, we discuss the resonance interaction energy and force between two identical correlated atoms in the waveguide, one excited and the other in the ground state, prepared in their symmetric or antisymmetric superposition.

Giuseppe Fiscelli , Roberta Palacino, Roberto Passante, Lucia Rizzuto, Salvatore Spagnolo, and Wenting Zhou 1 Università degli Studi di Palermo, Dipartimento di Fisica e Chimica, Via Archirafi 36, I-90123 Palermo, Italia 2 INFN, Laboratori Nazionali del Sud, I-95123 Catania, Italy 3 SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom 4 Università degli Studi di Palermo, Dipartimento di Energia, Ingegneria dell’Informazione e Modelli Matematici, Viale delle Scienze, Edificio 9, I-90128 Palermo, Italia and 5 Center for Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211, China

We consider the time-dependent resonance interaction energy between two identical atoms, one in the ground state and the other in an excited state, and interacting with the vacuum electromagnetic field, during a nonequilibrium situation such as the dynamical atomic self-dressing process. We suppose the two atoms prepared in a correlated, symmetric or antisymmetric, state. Since the atoms start from a nonequilibrium conditions, their interaction energy is time dependent. We obtain, at second order in the atom-field coupling, an analytic expression for the time-dependent resonance interaction energy between the atoms. We show that this interaction vanishes when the two atoms are outside the light-cone of each other, in agreement with relativistic causality, while it instantaneously settles to its stationary value after time $t=R/c$ ($R$ being the interatomic distance), as obtained in a time-independent approach. We also investigate the time-dependent electric energy density in the space around the two correlated atoms, in both cases of antisymmetric (subradiant) and symmetric (superradiant) states, during the dressing process of our two-atom system. We show that the field energy density vanishes in points outside the light-cone of both atoms, thus preserving relativistic causality. On the other hand, inside the light-cone of both atoms, the energy density instantaneously settles to its stationary value. Specifically, for points at equal distance from the two atoms, we find that it vanishes if the two atoms are prepared in the antisymmetric (subradiant) state, while it is enhanced, with respect to the case of atoms in a factorized state, in the symmetric (superradiant) state. The physical meaning of these results is discussed in detail in terms of interference effects of the field emitted by the two atoms.

In this paper we discuss and review several aspects of the effect of boundary conditions and structured environments on dispersion and resonance interactions involving atoms or molecules, as well as on vacuum field fluctuations. We first consider the case of a perfect mirror, which is free to move around an equilibrium position and whose mechanical degrees of freedom are treated quantum mechanically. We investigate how the quantum fluctuations of the mirror's position affect vacuum field fluctuations for both a one-dimensional scalar and electromagnetic field, showing that the effect is particularly significant in the proximity of the moving mirror. This result can be also relevant for possible gravitational effects, since the field energy density couples to gravity. We stress that this interaction-induced modification of the vacuum field fluctuations can be probed through the Casimir-Polder interaction with a polarizable body, thus allowing to detect the effect of the mirror's quantum position fluctuations. We then consider the effect of an environment such as an isotropic photonic crystal or a metallic waveguide, on the resonance interaction between two entangled identical atoms, one excited and the other in the ground state. We discuss the strong dependence of the resonance interaction with the relative position of the atomic transition frequency with the gap of the photonic crystal in the former case, and with the cut-off frequency of waveguide in the latter.

A novel Partial Discharge detection system is here described. The system employs a special wideband antenna as a sensor, allowing to sense either Partial Discharges pulses either the AC supply voltage at a distance from the component under test, so avoiding the need of direct connection or component shutdown. Thanks to its wireless nature and small physical dimensions, the system enables to perform accurate on-line Partial Discharge diagnosis even in circumstances where conventional instrumentation would be impractical to use, so greatly extending the applicability of this diagnostic method.

The design, implementation and characterization of a digital waveform recorder for ocean bottom seismic monitoring is here reported. The system is capable of synchronously acquiring, and logging on a flash memory bank, four high resolution signals. Thanks to a very careful design of the system architecture and by using robust digital signal processing techniques, two main conflicting issues have been addressed: a high dynamic range, better than 120 dB, usually obtained with high energy demanding converters, and a power consumption as low as 250 mW, hence allowing to easily increase the time of a continuous submarine monitoring session up to 3 months.

A very compact and high performance datalogger for automotive in-vehicle testing is here described. The small logger dimensions and the availability of a CAN interface allows to easily implement multiple and distributed acquisition schemes, very challenging with traditional instrumentation. High acquisition rate, up to 100 Ksps/ch, and low cost was obtained through a very accurate hardware and software design.

A systematic evaluation of the potential energy saving and CO2 emissions reduction on buildings was carried out, when a renewable energy system is locally installed. The exploitation of a combined solar and photovoltaic system and the integration of suitable energy management actions were deeply investigated. A model of these solar and photovoltaic components has been developed and included within a complete house simulator, capable to precisely figure out the daily electric energy consumptions of typical apartments and to measure the positive actions induced by the added renewable energy. Saving up to 40% on the energy consumptions and even more savings on wiring losses seems to be easily obtainable.

A novel impedance measurement method based on random sampling of voltage and current signals is proposed. This technique dramatically reduces the sampling frequency requirements, thus circumventing the limitations imposed by maximum speed of the analog to digital converter and the signal processing unit. The lowering of the sampling frequencies allows the design and the implementation of an almost all digital architecture by using a simple microprocessor based embedded system and a digital frequency synthesizer. The basic principles are presented, and the implemented algorithms are described. Experimental results show the instrument performances compared to others commercial alternatives.

A prototype of a Software Defined Radio (SDR) platform has been successfully designed and tested implementing a reconfigurable IEEE 802.11 and ZigBee receiver. The system exploits the reconfiguration capability of an FPGA for implementing a number of receiver configurations that share the. same RF front-end. Configurations can be switched at run time, or can share the available logic and radio resource.

In order to obtain CO2 emissions reductions, energy management control actions inside apartments and detached houses have to be carried out. In this work, new control actions devoted to the reduction of electrical energy consumptions inside typical Italian apartments are proposed. These "Distributed on Site" (DoS) actions consist in employing specific control strategies to smartly exploit the hot water provided by a solar panel, the electricity generated by a photovoltaic panel and the delayed starting of appliances.