Quantum correlations in continuos-time quantum walks of two indistinguishable particles

We evaluate the degree of quantum correlation between two fermions (bosons) subject to continuous time quantum walks in a one-dimensional ring lattice with periodic boundary conditions. In our approach, no particle-particle interaction is considered. We show that the interference effects due to exchange symmetry can result into the appearance of non-classical correlations. The role played onto the appearance of quantum correlations by the quantum statistics of the particles, the boundary conditions, and the partition of the system is widely investigated. Quantum correlations also been investigated in a model mimicking the ballistic evolution of two indistinguishable particles in a 1D continuous space structure. Our results are consistent with recent quantum optics and electron quantum optics experiments where the showing up of two-particle non-classical correlations has been observed even in the absence of mutual interaction between the particles.Comment: 12 pages, 5 figure

Non-Markovian continuous-time quantum walks on lattices with dynamical noise

We address the dynamics of continuous-time quantum walks on one-dimensional disordered lattices inducing dynamical noise in the system. Noise is described as time-dependent fluctuations of the tunneling amplitudes between adjacent sites, and attention is focused on non-Gaussian telegraph noise, going beyond the usual assumption of fast Gaussian noise. We observe the emergence of two different dynamical behaviors for the walker, corresponding to two opposite noise regimes: slow noise (i.e. strong coupling with the environment) confines the walker into few lattice nodes, while fast noise (weak coupling) induces a transition between quantum and classical diffusion over the lattice. A phase transition between the two dynamical regimes may be observed by tuning the ratio between the autocorrelation time of the noise and the coupling between the walker and the external environment generating the noise. We also address the non-Markovianity of the quantum map by assessing its memory effects, as well as evaluating the information backflow to the system. Our results suggest that the non-Markovian character of the evolution is linked to the dynamical behavior in the slow noise regime, and that fast noise induces a Markovian dynamics for the walker.Comment: 10 pages, 8 figure

Gerusalemme: confini dello spazio e confini dell'anima

2009/2010Nella reltà di Gerusalemme, si sono voluti ricercare i confini della città. Fenomeno sia spaziale che metafisico, il confine a Gerusalemme condiziona la vita quotidiana. Stratificati dalla storia hanno contribuito alla formazione di distinte identità. La ricerca della sua funzione, tra le molteplici cui è destinato, nell'ambirto della città santa ed i suoi effetti geografici e simbolici.XXII Cicl

Noisy quantum walks of two indistinguishable interacting particles

We investigate the dynamics of continuous-time two-particle quantum walks on a one-dimensional noisy lattice. Depending on the initial condition, we show how the interplay between particle indistinguishability and interaction determines distinct propagation regimes. A realistic model for the environment is considered by introducing non-Gaussian noise as time-dependent fluctuations of the tunneling amplitudes between adjacent sites. We observe that the combined effect of particle interaction and fast noise (weak coupling with the environment) provides a faster propagation compared to the noiseless case. This effect can be understood in terms of the band structure of the Hubbard model, and a detailed analysis as a function of both noise and system parameters is presented.Comment: 9 pages, 8 figure

Comment on \u201cA new device for administration of continuous positive airway pressure in preterm infants\u201d by Trevisanuto et al

We read with interest the contribution by Trevisanuto et al. [1] on the effectiveness of a new device for administering continuous positive airway pressure (CPAP) as an alternative to conventional nasal CPAP in ameliorating comfort in preterm infants needing continuous distending pressure. The data which they present are intriguing, but a few points need to be further discussed. First, the use of a \u201ccomfort scale\u201d appears to be a surrogate end-point. To properly assess safety and efficacy of this new technique, even in a pilot study, the authors should have focused on more relevant clinical aspects or potential complications, such as level of respiratory distress, oxygen-dependency, rate of apnea, local damage, air leak, or need for mechanical ventilation. Second, the authors reported a marked reduction in the Neonatal Infant Pain Scale (NIPS) values, i.e., a better comfort status of patients, during treatment with helmet CPAP. Given the lower level of stress imposed by this technique, one might have expected some modifications in the main physiological parameters, such as heart rate, respiratory rate, and arterial blood pressure [2]. On the other hand, none of the investigated parameters differed between the two CPAP treatments, raising doubts about potential bias due to the nonblinded scoring method used in this study. Indeed, NIPS does require a close observation of the infant, making any blinding process quite complex. Such important limitation might be partially circumvented by simultaneous NIPS measurements performed by two independent observers or by video recording. Third, the small number of enrolled patients (powered only for the chosen end-point), the very brief duration of both CPAP treatments, and the relatively healthy status of the population studied preclude any definitive conclusion about this study. Indeed, how would this technique work in sicker infants who may require CPAP continuously for days or weeks? What are the possible effects of long-term application on abdominal distension, or in the prevention of apnea episodes? As regards the latter point, we have had the contrary findings in a single preliminary experience. A premature infant (31weeks of postconceptional age) treated with conventional nasal CPAP (Infant-Flow-Driver, EME) for apnea of prematurity, was shifted to helmet CPAP due to poor tolerance of nasal prongs. However, after 2 h of treatment he had to be returned to nasal CPAP for repeated episodes of apnea and arterial O2 desaturation. Interestingly, as soon as conventional nasal CPAP was applied, the apneic episodes virtually disappeared. Of note, we report some difficulties in maintaining CPAP levels above 3 cmH2O, despite flow rates set as high as 15 lpm and absence of major leaks in the system. We speculate that conventional nasal CPAP, successfully used for apnea of prematurity [3], would be more effective than the new technique in these circumstances. In summary, we congratulate the authors for their original study. Nonetheless, their conclusion that the helmet CPAP \u201cseems to guarantee a better tolerability and at least similar improvement in oxygenation\u201d may be misleading for the reader. We believe that larger randomized controlled studies are needed to better define the role of this new device and to verify its potential superiority over conventional CPAP by means of more appropriate end-points

The political economy of regulatory stability in Argentina.

Beginning in 1989, Argentina committed itself to a wide-ranging program of utility privatization and the establishment of new regulatory regimes. Following the international best practice, the design of these regimes involved the creation of independent regulatory agencies and the delegation of important regulatory powers to these agencies. At the time these reforms were introduced, there was a reasonable amount of consensus that both privatization and the change in the locus of regulatory power were policy changes that had arrived to stay. Moreover, the expectation was that utility regulation would become more stable than in the past. In this thesis, however, it is demonstrated that these expectations were unfounded. Using deductive reasoning, it is proposed that although delegation to independent regulatory agencies is an important condition for developing stable regulatory policies, equally important for that purpose is ensuring that governments cannot easily reverse that delegation or manipulate its terms. It is also hypothesized that, in the case of Argentina, whether or not this second requirement can be satisfied depends on the legal instrument policy-makers use to define the key features of a regulatory regime. The final claim is that, given the country's institutional endowment, the way regulatory policy is defined has an important consequence. It is less likely to be reversed, and therefore be stable and predictable, if key features of the policy are defined in a statute, than if they are contained within other legal instruments that can be passed - and changed - unilaterally by the executive. To test these hypotheses, the thesis uses three case studies: telecommunications regulation between 1990 and 2001; electricity regulation between 1992 and 2001; and utility regulation - across sectors - between the passage of the Economic Emergency Law in January 2002 and April 2003

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UN GENERATORE DI PETTINE DI FREQUENZE PER L’ECCITAZIONE DI RIVELATORI DI FOTONI A BASSA ENERGIA

Il lavoro qui presentato, che nasce dalla collaborazione tra l’LNTS (Laboratorio Nuove Tecnologie e Strumenti) dell’INGV e il Dipartimento di Fisica dell’Università di Roma “La Sapienza”, descrive lo strumento realizzato per fornire il pettine di frequenze atto ad eccitare un sistema sperimentale per otto risuonatori KID. In tale sistema il pettine di frequenze verrà traslato nella banda di frequenza dei KIDs (nell’ordine dei GHz) per poterne effettuare l’eccitazione e quindi riportato nella banda iniziale per effettuarne l’acquisizione e l’analisi

A Comparison Between Deterministic and Stochastic Inversions of Phaseless Data for Microwave Imaging

The development of microwave imaging techniques and their application are strongly related to the possibility to realize fast and cheap measurement systems. On the contrary, the phase acquisition usually requires complex and expensive apparatus and it turns out to be critical especially at high frequencies. Moreover, holographic and interferometric methods, often used in optical applications [1], are usually characterized by a high computational burden because of the time‐consuming data post‐processing. Consequently, the study of efficient algorithms for the reconstruction from amplitude‐only data is necessary in several applications. Also published in: Progress In Electromagnetics Research Symposium Abstracts, Hangzhou, China, March 24-28, 200