Nonclassical Radiation from Thermal Cavities in the Ultrastrong Coupling Regime

Thermal or chaotic light sources emit radiation characterized by a slightly enhanced probability of emitting photons in bunches, described by a zero-delay second-order correlation function $g^{(2)}(0) = 2$. Here we explore photon-coincidence counting statistics of thermal cavities in the ultrastrong coupling regime, where the atom-cavity coupling rate becomes comparable to the cavity resonance frequency. We find that, depending on the system temperature and coupling rate, thermal photons escaping the cavity can display very different statistical behaviors, characterised by second-order correlation functions approaching zero or greatly exceeding two.Comment: results on frequency resolved photon correlations added, to appear in Phys. Rev. Let

A fully digital model for Kalman filters

The Kalman filter is a mathematical method, whose purpose is to process noisy measurements in order to obtain an estimate of some relevant parameters of a system. It represents a valuable tool in the GNSS area, with some of its main applications related to the computation of the user PVT solution and to the integration of GNSS receivers with INS or other sensors. The Kalman filter is based on a state space representation, that describes the analyzed system as a set of differential equations that establishes the connections between the inputs, the outputs and the state variables of the analyzed system. In the continuous time domain there exists a large class of physical processes with a time evolution well described by means of stochastic differential equations. A typical problem is the need for an equivalent system in the discrete time, due to the discrete nature of the data to be processed. In the literature, it is quite common to solve this problem in the continuous time domain and to approximate the solution using a Taylor series approximation, to obtain an approximate discrete time version of the continuous time problem. By the way, other methods exist, based on the possibility to transform a continuous-time system to a discrete-time system by means of transformations from the Laplace complex plane to the z plane. These methods are widely used in the digital signal processing community, for example, to design digital filters from their analog counterparts. The main advantage of this approach is that it is very easily implemented by applying some mechanical rules. Moreover the nature of the approximation introduced by the Laplace-z transformation is a-priori known and clearly readable in the frequency domain. In the following the classical methods based on the Taylor approximation and on the Laplace-z transformations will be analyzed and compare

Sulle rotte del Mediterraneo. Infrastrutture e vie di comunicazione nel Mare Nostrum dall’antichità ad oggi

Le scoperte geo-etnografice finanziate dai grandi sovrani di Egitto e di Persia, piuttosto che tessere il disegno di singole occupazioni territoriali, erano intese a costituire una grande e complessa rete di relazioni. Ma fu poi Roma a dare massimo impulso alla navigazione infra-mediterranea, fornendo per la prima volta autorevoli risposte politiche e militari alle esigenze che tutt’oggi caratterizzano i traffici navali in quest’area del pianeta: all’insegna del principio “navigare necesse est”, i Romani imposero il concetto di sicurezza marittima, sgominando i pirati che rendevano in precedenza le rotte insicure e pericolose, e quello di liberalizzazione dei traffici commerciali, della pesca e della nautica da diporto, trasformando un mare ampio e bellicoso in un tranquillo lago interno brulicante di vita. Pompeo uccise 10.000 pirati e fu soprannominato dai Romani “pacificatore del mare”. Sembra incredibile che 2000 anni dopo, nonostante tecnologie belliche da fantascienza, le attuali superpotenze non riescano a fare altrettanto nel Golfo Persico. Altra rotta importante del Medioevo fu quella delle crociate, dal Nordovest verso la Terrasanta; anche lungo questa rotta lo Stretto di Messina ebbe un ruolo fondamentale, come attestato dall’edificazione dell’Ospedale dei Cavalieri Templari in Messina, oggi Chiesa sconsacrata di S. Maria Alemanna, tra i più antichi esempi di gotico siciliano. La fortuna dei porti franchi di Livorno, Ancona, Nizza e Trieste dipese – come capirono gli stessi che li promossero – non solo dalle franchigie doganali, ma anche dalla forza di attrazione da essi esercitata verso capitali e mercanti, di cui Genova e Venezia disponevano in larga misura

Emergence of entanglement from a noisy environment: The case of polaritons

We show theoretically that polariton pairs with a high degree of polarization entanglement can be produced through parametric scattering. We demonstrate that it can emerge in coincidence experiments, even at low excitation densities where the dynamics is dominated by incoherent photoluminesce. Our analysis is based on a microscopic quantum statistical approach that treats coherent and incoherent processes on an equal footing, thus allowing for a quantitative assessment of the amount of entanglement under realistic experimental conditions. This result puts forward the robustness of pair correlations in solid-state devices, even when noise dominates one-body correlations.Comment: revised version. new figure