893 research outputs found

    Improving randomness characterization through Bayesian model selection

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    Nowadays random number generation plays an essential role in technology with important applications in areas ranging from cryptography, which lies at the core of current communication protocols, to Monte Carlo methods, and other probabilistic algorithms. In this context, a crucial scientific endeavour is to develop effective methods that allow the characterization of random number generators. However, commonly employed methods either lack formality (e.g. the NIST test suite), or are inapplicable in principle (e.g. the characterization derived from the Algorithmic Theory of Information (ATI)). In this letter we present a novel method based on Bayesian model selection, which is both rigorous and effective, for characterizing randomness in a bit sequence. We derive analytic expressions for a model's likelihood which is then used to compute its posterior probability distribution. Our method proves to be more rigorous than NIST's suite and the Borel-Normality criterion and its implementation is straightforward. We have applied our method to an experimental device based on the process of spontaneous parametric downconversion, implemented in our laboratory, to confirm that it behaves as a genuine quantum random number generator (QRNG). As our approach relies on Bayesian inference, which entails model generalizability, our scheme transcends individual sequence analysis, leading to a characterization of the source of the random sequences itself.Comment: 25 page

    Enhanced Production of Runaway Electrons during a Disruptive Termination of Discharges Heated with Lower Hybrid Power in the Frascati Tokamak Upgrade

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    4 pages, 4 figures.-- PACS nrs.: 52.55.Fa, 52.35.Py, 52.50.Sw, 52.55.Pi.We report on the observation of a large production of runaway electrons during a disruptive termination of discharges heated with lower-hybrid waves at the Frascati Tokamak Upgrade. The runaway current plateaus, which can carry up to 80% of the predisruptive current, are observed more often than in normal Ohmic disruptions. The largest runaway currents correspond to the slowest plasma current decay rates. This trend is opposite to what is observed in most tokamaks. We attribute this anomalous behavior to the acceleration of the preexistent wave-resonant suprathermal electrons during the disruption decay phase. These results could be relevant for the operation of the ITER tokamak whenever a sizeable amount of lower-hybrid power is made available.Research supported in part by Spanish DGES Project No. FTN2003-04587. This work was also supported by the Euratom Communities under the contract of association between EURATOM and ENEA.Publicad

    Precise bounds on the Higgs boson mass

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    We study the renormalization group evolution of the Higgs quartic coupling λH\lambda_{H} and the Higgs mass mHm_{H} in the Standard Model. The one loop equation for λH\lambda_{H} is non linear and it is of the Riccati type which we numerically and analytically solve in the energy range [mt,EGU][m_{t},E_{GU}] where mtm_{t} is the mass of the top quark and EGU=1014E_{GU}=10^{14} GeV. We find that depending on the value of λH(mt)\lambda_{H}(m_{t}) the solution for λH(E)\lambda_{H}(E) may have singularities or zeros and become negative in the former energy range so the ultra violet cut off of the standard model should be below the energy where the zero or singularity of λH\lambda_{H} occurs. We find that for 0.369λH(mt)0.6130.369\leq\lambda_{H}(m_{t})\leq0.613 the Standard Model is valid in the whole range [mt,EGU][m_{t},E_{GU}]. We consider two cases of the Higgs mass relation to the parameters of the standard model: (a) the effective potential method and (b) the tree level mass relations. The limits for λH(mt)\lambda_{H}(m_{t}) correspond to the following Higgs mass relation 150mH193150\leq m_{H}\lessapprox 193 GeV. We also plot the dependence of the ultra violet cut off on the value of the Higgs mass. We analyze the evolution of the vacuum expectation value of the Higgs field and show that it depends on the value of the Higgs mass. The pattern of the energy behavior of the VEV is different for the cases (a) and (b). The behavior of λH(E)\lambda_{H}(E), mH(E)m_{H}(E) and v(E)v(E) indicates the existence of a phase transition in the standard model. For the effective potential this phase transition occurs at the mass range mH180m_{H}\approx 180 GeV and for the tree level mass relations at mH168m_{H}\approx 168 GeV.Comment: 14 pages, 7 figures. Expanded the discussion of the Higgs mass relation between the parameters of the Standard Model. Included the method of the Higgs effective potentia

    Proposal for automated transformations on single-photon multipath qudits

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    COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPWe propose a method for implementing automated state transformations on single-photon multipath qudits encoded in a one-dimensional transverse spatial domain. It relies on transferring the encoding from this domain to the orthogonal one by applying a spatial phase modulation with diffraction gratings, merging all the initial propagation paths by using a stable interferometric network, and filtering out the unwanted diffraction orders. The automation feature is attained by utilizing a programmable phase-only spatial light modulator (SLM) where properly designed diffraction gratings displayed on its screen will implement the desired transformations, including, among others, projections, permutations, and random operations. We discuss the losses in the process which is, in general, inherently nonunitary. Some examples of transformations are presented and, considering a realistic scenario, we analyze how they will be affected by the pixelated structure of the SLM screen. The method proposed here enables one to implement much more general transformations on multipath qudits than is possible with a SLM alone operating in the diagonal basis of which-path states. Therefore, it will extend the range of applicability for this encoding in high-dimensional quantum information and computing protocols as well as fundamental studies in quantum theory.963113COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçãoSem informação2014/27223-22016/24162-8The authors thank J. Condé for the discussions, comments, and interest in this proposal and M. T. Cunha, R. Rabelo, and A. Cabello for useful discussions and important remarks. This research was supported by CAPES, CNPq, and FAPEMIG. M.A.S.-P. acknowledges financial support from Millennium Scientific Initiative (Grant No. RC130001) and FONDECyT (Grant No. 3170400), and B.M. acknowledges financial support from FAPESP (No. 2014/27223-2). R.D.B. is supported by FAPESP (No. 2016/24162-8)
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