Elliptical orbits in the Bloch sphere

As is well known, when an SU(2) operation acts on a two-level system, its Bloch vector rotates without change of magnitude. Considering a system composed of two two-level systems, it is proven that for a class of nonlocal interactions of the two subsystems including \sigma_i\otimes\sigma_j (with i,j \in {x,y,z}) and the Heisenberg interaction, the geometric description of the motion is particularly simple: each of the two Bloch vectors follows an elliptical orbit within the Bloch sphere. The utility of this result is demonstrated in two applications, the first of which bears on quantum control via quantum interfaces. By employing nonunitary control operations, we extend the idea of controllability to a set of points which are not necessarily connected by unitary transformations. The second application shows how the orbit of the coherence vector can be used to assess the entangling power of Heisenberg exchange interaction.Comment: 9 pages, 4 figures, few corrections, J. Opt. B: Quantum Semiclass. Opt. 7 (2005) S1-S

Quantum Integrals of Motion for Variable Quadratic Hamiltonians

We construct the integrals of motion for several models of the quantum damped oscillators in nonrelativistic quantum mechanics in a framework of a general approach to the time-dependent Schroedinger equation with variable quadratic Hamiltonians. An extension of Lewis-Riesenfeld dynamical invariant is given. The time-evolution of the expectation values of the energy related positive operators is determined for the oscillators under consideration. A proof of uniqueness of the corresponding Cauchy initial value problem is discussed as an application.Comment: 32 pages, no figure

Compatible Transformations for a Qudit Decoherence-free/Noiseless Encoding

The interest in decoherence-free, or noiseless subsystems (DFS/NSs) of quantum systems is both of fundamental and practical interest. Understanding the invariance of a set of states under certain transformations is mutually associated with a better understanding of some fundamental aspects of quantum mechanics as well as the practical utility of invariant subsystems. For example, DFS/NSs are potentially useful for protecting quantum information in quantum cryptography and quantum computing as well as enabling universal computation. Here we discuss transformations which are compatible with a DFS/NS that is composed of d-state systems which protect against collective noise. They are compatible in the sense that they do not take the logical (encoded) states outside of the DFS/NS during the transformation. Furthermore, it is shown that the Hamiltonian evolutions derived here can be used to perform universal quantum computation on a three qudit DFS/NS. Many of the methods used in our derivations are directly applicable to a large variety of DFS/NSs. More generally, we may also state that these transformations are compatible with collective motions.Comment: 30 pages, replaced with published versio

Quantum key distribution based on orthogonal states allows secure quantum bit commitment

For more than a decade, it was believed that unconditionally secure quantum bit commitment (QBC) is impossible. But basing on a previously proposed quantum key distribution scheme using orthogonal states, here we build a QBC protocol in which the density matrices of the quantum states encoding the commitment do not satisfy a crucial condition on which the no-go proofs of QBC are based. Thus the no-go proofs could be evaded. Our protocol is fault-tolerant and very feasible with currently available technology. It reopens the venue for other "post-cold-war" multi-party cryptographic protocols, e.g., quantum bit string commitment and quantum strong coin tossing with an arbitrarily small bias. This result also has a strong influence on the Clifton-Bub-Halvorson theorem which suggests that quantum theory could be characterized in terms of information-theoretic constraints.Comment: Published version plus an appendix showing how to defeat the counterfactual attack, more references [76,77,90,118-120] cited, and other minor change

Epidemiological Data, Serovar Distribution and Antimicrobial Resistance Patterns of Salmonella Species in Children, Greece 2011-2017: A Retrospective Study

OBJECTIVE: This study aimed to describe Salmonella epidemiology and antimicrobial resistance in Greek children over the period of 2011-2017. MATERIALS AND METHODS: A 7-year retrospective study (2011-2017) was performed, based on data recorded by the National Reference Centre for Salmonella, among children aged ≤14 years. Epidemiological data, serovar distribution and antimicrobial resistance patterns were recorded. RESULTS: Overall, 2347 Salmonella isolates were collected (27 typhoid-paratyphoid). Salmonellosis cases increased by almost 2-fold in 2017 compared to 2011. The highest rates were reported in August, with infants being the most vulnerable group (17.9%). The majority of isolates were identified in stool samples (91%). Boys slightly outnumbered girls (˜1.05:1). Salmonella Enteritidis was the most prevalent serovar (28.5%), followed by Salmonella Typhimurium (12.2%) and Salmonella monophasic Typhimurium (10.4%). Non-typhoid isolates displayed low resistance rates to 3rd generation cephalosporins (1%) and ciprofloxacin (0.3%), while the corresponding resistance of typhoid isolates was 10% and 5% respectively. An increasing trend of Salmonella monophasic Typhimurium was recorded, associated with high rates of multidrug resistance, reaching a percentage of 97.8% in 2017. CONCLUSIONS: Salmonellosis epidemiology in Greek children is comparable to previously published European data. Antimicrobial resistance rates to 3rd-generation cephalosporins and ciprofloxacin for non-typhoid and typhoid-paratyphoid remain low. Notably, there is an increasing prevalence of Salmonella monophasic Typhimurium isolates, associated with multiple antimicrobial resistance. Copyright © 2020 by Academy of Sciences and Arts of Bosnia and Herzegovina

Typing of Pseudomonas aeruginosa strains isolated from Greek water samples by three typing methods: serotyping, Random Amplified Polymorphic DNA (RAPD) and Pulsed Field Gel Electrophoresis (PFGE)

The study of various types of Pseudomonas aeruginosa strains isolated from water environments is of paramount importance from a public health point of view, due to their ubiquity and pathogenicity. Molecular (Random Amplified Polymorphic DNA and Pulsed Field Gel Electrophoresis) and phenotypical (serotyping) typing methods were applied to environmental P. aeruginosa strains. The typeability and discriminatory power of the methods were studied and compared. The two molecular methods managed to type a number of P. aeruginosa strains which were non-serotypeable due to their rough phenotypes. According to our results, the combination of phenotypic and genotypic methods increased the reliability of the results, yielding several different clones that seem to circulate in Greek water environments

The use of bacteriophages for monitoring the microbiological quality of sewage sludge

The use of bacteriophages as potential indicators of faecal pollution has recently been studied. The correlation of the number of bacterial indicators and the presence of three groups of bacteriophages, namely somatic coliphages (SOMCPH), F-RNA specific phages (FRNAPH) and phages of Bacteroides fragilis (BFRPH), in raw and treated sludge is presented in this study. Raw and anaerobically digested sewage sludge samples from two wastewater treatment plants in Athens were collected on a monthly basis, over a 2-year period, and analyzed for total coliforms, Ecoli, intestinal enterococci and the three groups of bacteriophages. A clear correlation between the number of bacterial indicators and the presence of bacteriophages was observed. E.coli concentrations of >= 10’ cfus g(-1) and < 10(3) cfus g(-1) comprise a threshold for the presence of FRNAPH and BFRPH, respectively. Likewise, intestinal enterococci concentrations of >= 10(4) cfus g(3) and < 10(3) cfus g(-1) comprise a threshold for the presence of FRNAPH and BFRPH, respectively. In the case of SOMCPH, it was not possible to define a threshold, since they were detected with the lowest observed indicator concentrations in all samples