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A novel approximation scheme is proposed to describe the dynamics of the spin-boson problem. Being nonperturbative in the coupling strength nor in the tunneling frequency, it gives reliable results over a wide regime of temperatures and coupling strength to the thermal environment for a large class of bath spectral densities. We use a path-integral approach and start from the exact solution for the two-level system population difference in the form of a generalized master equation (GME). Then, we approximate inter-blip and blip-sojourns interactions up to linear order, while retaining all intra-blip correlations to find the kernels entering the GME in analytical form. Our approximation scheme, which we call Weakly-Interacting Blip Approximation (WIBA), fully agrees with conventional perturbative approximations in the tunneling matrix element (Non-Interacting Blip Approximation) or in the system-bath coupling strength.Comment: 15 pages, 14 figure

We investigate the phase coherence of a trapped Bose-Einstein condensate that undergoes a dynamical superfluid-insulator transition in the presence of a one-dimensional optical lattice. We study the evolution of the condensate after a sudden displacement of the harmonic trapping potential by solving the Gross-Pitaevskii equation, and comparing the results with the prediction of two effective 1D models. We show that, owing to the 3D nature of the system, the breakdown of the superfluid current above a critical displacement is not associated to a sharp transition, but there exists a range of displacements for which the condensate can recover a certain degree of coherence. We also discuss the implications on the interference pattern after the ballistic expansion as measured in recent experiments at LENS.

Abstract. -We present a novel approximation scheme to describe the influence of a harmonic bath on the dynamics of a two-level particle over almost the whole regime of temperatures and coupling to the environment, for a wide class of bath spectral densities. Starting from the exact path-integral solution for the two-level system density matrix, effective intra-blip correlations are fully included, while inter-blip and blip-sojourn interactions are considered up to first order. In the proper regimes, an excellent agreement with conventional perturbative approaches and ab-initio path-integral results is found.Introduction. -The problem of a two-level system (TLS) suffering from environmental decohering effects is ubiquitous to many physical and chemical situations [1][2][3]. Standard examples involve electron and proton transfer reaction in condensed phases [4], defect tunneling in metals [5] or tunneling systems in glasses [6,7]. Recently, several realizations of TLSs have been experimentally demonstrated in superconducting [8] and semiconducting [9] devices as possible unit (quantum bit) for future quantum computers. In these solid state systems, decoherence is a major obstacle towards the realization of a usable quantum computer [10][11][12]. Hence, a proper understanding of dissipation over a broad parameter regime is of outermost importance.For a description of the dissipative dynamics the spinboson model, in which the TLS is bilinearly coupled to a harmonic bath, is very frequently used. It reads [1][2][3]

Buildings have a central role to play in the energy transition driven by the European Commission with the introduction of the nearly zero-energy buildings notion for both new constructions and existing building stocks. Despite the growing interest in improving the energy performance of residential as well as office buildings, a research gap is identified in the field of the renovation of industrial buildings and facilities in terms of energy efficiency. A lack is recognized in terms of analysing the improvement of the work environment in all the areas that are not used as offices. Common decarbonisation strategies are usually adopted, as the electrification of some processes, the replacement of obsolete machinery or the implementation of renewable energy sources. However, reaching the ambitious levels set by the Energy Performance of Buildings Directive which aims at nearly zero-energy buildings, remains a challenge. The present paper aims to analyse the main barriers that hamper the development of highly energy efficient and decarbonised buildings in the productive sector and the effective deep energy renovations of industrial facilities. Moreover, it intends to highlight alternative strategies and opportunities and to underline potential benefits.