In this paper we discuss an approach to quantum computation where the basic information units (qubits and quregisters) are replaced by density operators and the restriction to unitary operators as logical gates is lifted through the introduction of the more general concept of quantum operation ( [17], [1]). This perspective is especially suited to provide a physical description of open systems....

– The analysis of dissipation and dephasing in driven mesoscopic devices requires a distinction between two notions of quantum irreversibility. One (”Loschmidt echo”) is related to ”time reversal”, while the other is related to ”driving reversal”. In the latter context we define the time of maximum return (”compensation time”) which generalizes the notion of ”echo time”. Non-perturbative featur...

In this paper, MgB2 bulks were prepared with doped TiO2 nanoparticles surface-modified by 5-10% SiO2. Quantitative X-ray diffraction (XRD) analysis was performed to obtain the weight fraction of impurities using the Rietveld method. The effects of addition of TiO2/SiO2 nanoparticles on the critical temperature (Tc), the upper critical field (Hc2), and the irreversibility field (Hirr) as a funct...

It i s argued that computing machines inevitably involve devices which perform logical functions that do not have a single-valued inverse. This logical irreversibility i s associated with physical irreversibility and requires a minimal heat generation, per machine cycle, typically of the order of kT for each irreversible function. This dissipation serves the purpose of standardizing signals and...