Fast optimization of parametrized quantum optical circuits

Parametrized quantum optical circuits are a class of quantum circuits in which the carriers of quantum information are photons and the gates are optical transformations. Classically optimizing these circuits is challenging due to the infinite dimensionality of the photon number vector space that is associated to each optical mode. Truncating the space dimension is unavoidable, and it can lead to incorrect results if the gates populate photon number states beyond the cutoff. To tackle this issue, we present an algorithm that is orders of magnitude faster than the current state of the art, to recursively compute the exact matrix elements of Gaussian operators and their gradient with respect to a parametrization. These operators, when augmented with a non-Gaussian transformation such as the Kerr gate, achieve universal quantum computation. Our approach brings two advantages: first, by computing the matrix elements of Gaussian operators directly, we don't need to construct them by combining several other operators; second, we can use any variant of the gradient descent algorithm by plugging our gradients into an automatic differentiation framework such as TensorFlow or PyTorch. Our results will find applications in quantum optical hardware research, quantum machine learning, optical data processing, device discovery and device design.Comment: 21 pages, 10 figure

Hamiltonians for one-way quantum repeaters

Quantum information degrades over distance due to the unavoidable imperfections of the transmission channels, with loss as the leading factor. This simple fact hinders quantum communication, as it relies on propagating quantum systems. A solution to this issue is to introduce quantum repeaters at regular intervals along a lossy channel, to revive the quantum signal. In this work we study unitary one-way quantum repeaters, which do not need to perform measurements and do not require quantum memories, and are therefore considerably simpler than other schemes. We introduce and analyze two methods to construct Hamiltonians that generate a repeater interaction that can beat the fundamental repeaterless key rate bound even in the presence of an additional coupling loss, with signals that contain only a handful of photons. The natural evolution of this work will be to approximate a repeater interaction by combining simple optical elements.Comment: 8 pages, 3 figure

Modelli del contatto culturale nell’Africa romana; per una riflessione sulle ‘teologie’ africane

The aim of this paper is to reconsider and to put in its context the iconographic scheme with the meeting between Dionysus and Ariadne. The point of departure is an Attic black-figure amphora kept in Trieste’s Civici Musei di Storia ed Arte, which has been attributed to the Antimenes Painter (530-510 BC). In the following, we will discuss the beginning of this scheme by the theories of Cornelia Isler-Kerényi, which in several papers points out the Cycladic origin of the depiction with Dionysus and Ariadne. In greater detail, the scholar believes that there is a close connection between the scheme depicted in the Attic black-figure and a discussed Cycladic production, the Melian pottery. The critical review of this thesis raises interesting questions about the beginning and the development of this iconographic scheme, which are going to enjoy great fortune for all the VI century BC

Facial locations in ASL based on production and perception data

This study tests the phonological distinctiveness of eight facial locations in ASL, with both production and perception experiments. This kind of work is crucial because, due to scarceness of minimal pairs in sign languages, phonemic locations are difficult to determine. Moreover, claims made but not tested by previous theoretic models (Stokoe et al. 1960, Stokoe 1965, Battison et al. 1975, Battison 1978, Friedman 1977, Kegl & Wilbur 1976, Wilbur 1979, Sandler’s 1989, Brentari’s 1998) are here investigated, including whether locations that are predicted to be contrastive are indeed distinct (e.g. ‘chin’ vs ‘mouth’). The specific goal of the first experiment (elicited production) is to determine what are the places of articulation, the aim of the second experiment (perception) is to determine if these places are contrastive

Full characterization of the quantum spiral bandwidth of entangled biphotons

Spontaneous parametric down-conversion has been shown to be a reliable source of entangled photons. Among the wide range of properties shown to be entangled, it is the orbital angular momentum that is the focus of our study. We investigate, in particular, the bi-photon state generated using a Gaussian pump beam. We derive an expression for the simultaneous correlations in the orbital angular momentum, l, and radial momentum, p, of the down-converted Laguerre-Gaussian beams. Our result allows us, for example, to calculate the spiral bandwidth with no restriction on the geometry of the beams: l, p, and the beam widths are all free parameters. Moreover, we show that, with the usual paraxial and collinear approximations, a fully analytic expression for the correlations can be derived

Recovering full coherence in a qubit by measuring half of its environment

When quantum systems interact with the environment they lose their quantum properties, such as coherence. Quantum erasure makes it possible to restore coherence in a system by measuring its environment, but accessing the whole of it may be prohibitive: realistically one might have to concentrate only on an accessible subspace and neglect the rest. If that is the case, how good is quantum erasure? In this work we compute the largest coherence $\langle \mathcal C\rangle$ that we can expect to recover in a qubit, as a function of the dimension of the accessible and of the inaccessible subspaces of its environment. We then imagine the following game: we are given a uniformly random pure state of $n+1$ qubits and we are asked to compute the largest coherence that we can retrieve on one of them by optimally measuring a certain number $0\leq a\leq n$ of the others. We find a surprising effect around the value $a\approx n/2$: the recoverable coherence sharply transitions between 0 and 1, indicating that in order to restore full coherence on a qubit we need access to only half of its physical environment (or in terms of degrees of freedom to just the square root of them). Moreover, we find that the recoverable coherence becomes a typical property of the whole ensemble as $n$ grows.Comment: 4 pages, 5 figure

SERVICE LEARNING. AN INNOVATIVE MODEL FOR PHYSICAL EDUCATION TEACHER TRAINING

Physical education is the most effective means of providing all children and youth with the skills, attitudes, values, knowledge and understanding for lifelong participation in society» (Unesco, 2013, p.6). The degree courses in Motor and Sport Sciences for the training of future EF teachers must adopt innovative methodologies, capable of promoting situated, experiential and practical learning in real life situations and in the social dynamics of the culture to which they belong. The Service Learning (SL) pedagogical-didactic model, capable of effectively combining the promotion of meaningful learning and civic engagement in trainee teachers in its proposal as a service to the community, has been receiving considerable attention in recent years. The article aims to present the Service Learning model and its application in university courses for Physical Education teacher training, through an analysis of best practices implemented in international academic contexts