Unified Collision Model of Coherent and Measurement-based Quantum Feedback

We introduce a general framework, based on collision models and discrete CP-maps, to describe on an equal footing coherent and measurement-based feedback control of quantum mechanical systems. We apply our framework to prominent tasks in quantum control, ranging from cooling to Hamiltonian control. Unlike other proposed comparisons, where coherent feedback always proves superior, we find that either measurements or coherent manipulations of the controller can be advantageous depending on the task at hand. Measurement-based feedback is typically superior in cooling, whilst coherent feedback is better at assisting quantum operations. Furthermore, we show that both coherent and measurement-based feedback loops allow one to simulate arbitrary Hamiltonian evolutions, and discuss their respective effectiveness in this regard.Comment: 5+11 pages, 6 figure

Cavity optomechanics assisted by optical coherent feedback

We consider a wide family of optical coherent feedback loops acting on an optomechanical system operating in the linearized regime. We assess the efficacy of such loops in improving key operations, such as cooling, steady-state squeezing and entanglement, as well as optical to mechanical state transfer. We find that mechanical sideband cooling can be enhanced through passive, interferometric coherent feedback, achieving lower steady-state occupancies and considerably speeding up the cooling process; we also quantify the detrimental effect of non-zero delay times on the cooling performance. Steady state entanglement generation in the blue sideband can also be assisted by passive interferometric feedback, which allows one to stabilise otherwise unstable systems, though active feedback (including squeezing elements) does not help to this aim. We show that active feedback loops only allow for the generation of optical, but not mechanical squeezing. Finally, we prove that passive feedback can assist state transfer at transient times for red-sideband driven systems in the strong coupling regime.Comment: 12 Pages, 5 Figure

Dynamics and interaction of vortex lines in an elongated Bose-Einstein condensate

We study the real-time dynamics of vortex lines in a large elongated Bose-Einstein condensate (BEC) of sodium atoms using a stroboscopic technique. Vortices are spontaneously produced via the Kibble-Zurek mechanism in a quench across the BEC transition and then they slowly precess keeping their orientation perpendicular to the long axis of the trap as expected for solitonic vortices in a highly anisotropic condensate. Good agreement with theoretical predictions is found for the precession period as a function of the orbit amplitude and the number of condensed atoms. In configurations with two or more vortex lines, we see signatures of vortex-vortex interaction in the shape and visibility of the orbits. In addition, when more than two vortices are present, their decay is faster than the thermal decay observed for one or two vortices. The possible role of vortex reconnection processes is discussed.Comment: 4 pages, 4 figure

Training Future Engineers to Be Ghostbusters: Hunting for the Spectral Environmental Radioactivity

Although environmental radioactivity is all around us, the collective public imagination often associates a negative feeling to this natural phenomenon. To increase the familiarity with this phenomenon we have designed, implemented, and tested an interdisciplinary educational activity for pre-collegiate students in which nuclear engineering and computer science are ancillary to the comprehension of basic physics concepts. Teaching and training experiences are performed by using a 4" x 4" NaI(Tl) detector for in-situ and laboratory {\gamma}-ray spectroscopy measurements. Students are asked to directly assemble the experimental setup and to manage the data-taking with a dedicated Android app, which exploits a client-server system that is based on the Bluetooth communication protocol. The acquired {\gamma}-ray spectra and the experimental results are analyzed using a multiple-platform software environment and they are finally shared on an open access Web-GIS service. These all-round activities combining theoretical background, hands-on setup operations, data analysis, and critical synthesis of the results were demonstrated to be effective in increasing students' awareness in quantitatively investigating environmental radioactivity. Supporting information to the basic physics concepts provided in this article can be found at http://www.fe.infn.it/radioactivity/educational

La rappresentazione dell’universo “no-vax” nella sfera pubblica digitale: una riflessione sul caso del vaccino anti COVID

Il dibattito sui vaccini in Italia è un caso di studio interessante per comprendere alcune dinamiche di funzionamento della sfera pubblica contemporanea. In apparenza, esso vede contrapporsi due schieramenti che esprimono posizioni totalmente inconciliabili e pare dunque rappresentare un ulteriore momento di messa in discussione del modello razionale di sfera pubblica nel contesto delle democrazie occidentali. L’obiettivo del nostro contributo è duplice: da un lato, vogliamo mettere in evidenza i limiti di una tale rappresentazione del fenomeno e, dall’altro, comprendere i meccanismi attraverso i quali essa è stata costruita nell’informazione online. Nella prima parte del contributo riprendiamo il dibattito sul concetto di sfera pubblica, con l’obiettivo di individuare un modello il più possibile adeguato alla sua interpretazione nella società contemporanea, dove la discussione si configura spesso nei termini di una contrapposizione tra posizioni stereotipate. La seconda sezione è deputata a descrivere alcuni dei meccanismi tipici della comunicazione online che tendono a esasperare tale tendenza. Nell’ultimo paragrafo illustriamo i risultati della ricerca empirica da noi condotta, avente lo scopo di ricostruire la resa mediatica delle posizioni dell’universo antivaccinista nei confronti del vaccino anti COVID-19. Dall’analisi dei 55 articoli apparsi su testate online, nel periodo compreso tra il primo gennaio 2020 e l’8 novembre 2020, abbiamo individuato quattro diverse categorie di articoli. Benché differenti nei contenuti e nelle forme di ricostruzione dell’universo “no-vax”, ognuna di esse ha fornito una rappresentazione caricaturale e artificiosa del movimento antivaccinista: a esso è stato attribuito un ampio ventaglio di posizioni spesso estremizzate e a volte in contraddizione tra loro, nonostante i suoi rappresentanti non si fossero espressi sul tema. Tale dibattito, dunque, non è apparso strutturato soltanto sulla base dei meccanismi già discussi in letteratura ma, almeno in alcuni casi, è emerso come le posizioni “estreme” delle parti in causa vengano costruite anche in assenza di esplicite dichiarazioni

Meynert's Nucleus Complex White Matter Abnormalities in Autism Spectrum Disorders: An MRI Study

Introduction: Cholinergic dysfunction has been proposed to play a role in autistic symtomatology. However, to date, its structural correlates are poorly understood. Methods: Twenty-five low-functioning, non-verbal males with Autism Spectrum Disorders (ASD) and 25 controls were enrolled in the study. All underwent MR T1-weighted 3D Structural Imaging and Diffusion Tensor Imaging. Grey and white matter components of the Meynert's Nucleus Complex were then identified on MR images, and both grey matter density and white matter mean Fractional Anisotropy in the Meynert's Nucleus region of interest were quantified for each subject. Non-verbal IQ was assessed in all subjects with ASD. Results: We showed reduced white matter Fractional Anisotropy in the bundles surrounding the Meynert's Nucleus in ASD subjects compared to controls. Fractional Anisotropy in these bundles was positively associated with non-verbal IQ, independently from whole brain white matter mean Fractional Anisotropy. ASD subjects did not show significant abnormalities in Meynert's Nucleus grey matter density. Conclusions: Our findings suggest that white matter abnormalities in the Meynert's Nucleus might be involved in the cholinergic deficits of ASD

Characterization of bipartite states using a single homodyne detector

We suggest a scheme to reconstruct the covariance matrix of a two-mode state using a single homodyne detector plus a polarizing beam splitter and a polarization rotator. It can be used to fully characterize bipartite Gaussian states and to extract relevant informations on generic states.Comment: 7 pages, 1 figur

Proposal of a novel approach to reference instrument and procedure definition to measure hydrogen volume and volumetric flow in a legal metrology framework

International standards concerning hydrogen measurement in legal frameworks are still lacking. This study proposes a novel approach to instrument and procedure definition for the legal measurement of pure hydrogen volume and volumetric flow rate according to main international standards of metrology. A wet drum meter filled with water is chosen as reference meter. The selected reference instrumentation and procedures are replicable in other laboratories. Simulations and calculations demonstrate that hydrogen diffusivity in water have no influence on error estimations, while water evaporation is considered because it affects the volumetric flow rate measurement. The expanded uncertainty of the total metrological chain is less than 0.25%. This reference procedure allows to perform tests for error of indication of new meters both using hydrogen and other flowing gases with the same measurement principle, instrumentation and procedures, helping the development and certification processes of new products useful for the upcoming energy transition