Quantum autoencoders via quantum adders with genetic algorithms

The quantum autoencoder is a recent paradigm in the field of quantum machine learning, which may enable an enhanced use of resources in quantum technologies. To this end, quantum neural networks with less nodes in the inner than in the outer layers were considered. Here, we propose a useful connection between approximate quantum adders and quantum autoencoders. Specifically, this link allows us to employ optimized approximate quantum adders, obtained with genetic algorithms, for the implementation of quantum autoencoders for a variety of initial states. Furthermore, we can also directly optimize the quantum autoencoders via genetic algorithms. Our approach opens a different path for the design of quantum autoencoders in controllable quantum platforms

Quantum levitation by left-handed metamaterials

Left-handed metamaterials make perfect lenses that image classical electromagnetic fields with significantly higher resolution than the diffraction limit. Here we consider the quantum physics of such devices. We show that the Casimir force of two conducting plates may turn from attraction to repulsion if a perfect lens is sandwiched between them. For optical left-handed metamaterials this repulsive force of the quantum vacuum may levitate ultra-thin mirrors

Chiral properties of hematite ({\alpha}-Fe2O3) inferred from resonant Bragg diffraction using circularly polarized x-rays

Chiral properties of the two phases - collinear motif (below Morin transition temperature, TM=250 K) and canted motif (above TM) - of magnetically ordered hematite ({\alpha}-Fe2O3) have been identified in single crystal resonant x-ray Bragg diffraction, using circular polarized incident x-rays tuned near the iron K-edge. Magneto-electric multipoles, including an anapole, fully characterize the high-temperature canted phase, whereas the low-temperature collinear phase supports both parity-odd and parity-even multipoles that are time-odd. Orbital angular momentum accompanies the collinear motif, while it is conspicuously absent with the canted motif. Intensities have been successfully confronted with analytic expressions derived from an atomic model fully compliant with chemical and magnetic structures. Values of Fe atomic multipoles previously derived from independent experimental data, are shown to be completely trustworthy

Measurements of thermodynamic and transport properties of EuC2_2: a low-temperature analogue of EuO

EuC$_2$ is a ferromagnet with a Curie-temperature of $T_C \simeq 15\,$K. It is semiconducting with the particularity that the resistivity drops by about 5 orders of magnitude on cooling through $T_C$, which is therefore called a metal-insulator transition. In this paper we study the magnetization, specific heat, thermal expansion, and the resistivity around this ferromagnetic transition on high-quality EuC$_2$ samples. At $T_C$ we observe well defined anomalies in the specific heat $c_p(T)$ and thermal expansion $\alpha(T)$ data. The magnetic contributions of $c_p(T)$ and $\alpha(T)$ can satisfactorily be described within a mean-field theory, taking into account the magnetization data. In zero magnetic field the magnetic contributions of the specific heat and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in finite fields. From an estimation of the pressure dependence of $T_C$ via Ehrenfest's relation, we expect a considerable increase of $T_C$ under applied pressure due to a strong spin-lattice coupling. Furthermore the influence of weak off stoichiometries $\delta$ in EuC$_{2 \pm \delta}$ was studied. It is found that $\delta$ strongly affects the resistivity, but hardly changes the transition temperature. In all these aspects, the behavior of EuC$_2$ strongly resembles that of EuO.Comment: 7 pages, 6 figure

Casimir forces on a silicon micromechanical chip

Quantum fluctuations give rise to van der Waals and Casimir forces that dominate the interaction between electrically neutral objects at sub-micron separations. Under the trend of miniaturization, such quantum electrodynamical effects are expected to play an important role in micro- and nano-mechanical devices. Nevertheless, utilization of Casimir forces on the chip level remains a major challenge because all experiments so far require an external object to be manually positioned close to the mechanical element. Here, by integrating a force-sensing micromechanical beam and an electrostatic actuator on a single chip, we demonstrate the Casimir effect between two micromachined silicon components on the same substrate. A high degree of parallelism between the two near-planar interacting surfaces can be achieved because they are defined in a single lithographic step. Apart from providing a compact platform for Casimir force measurements, this scheme also opens the possibility of tailoring the Casimir force using lithographically defined components of non-conventional shapes

Prototyping of petalets for the Phase-II Upgrade of the silicon strip tracking detector of the ATLAS Experiment

In the high luminosity era of the Large Hadron Collider, the HL-LHC, the instantaneous luminosity is expected to reach unprecedented values, resulting in about 200 proton-proton interactions in a typical bunch crossing. To cope with the resultant increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The ITk consists of a silicon pixel and a strip detector and exploits the concept of modularity. Prototyping and testing of various strip detector components has been carried out. This paper presents the developments and results obtained with reduced-size structures equivalent to those foreseen to be used in the forward region of the silicon strip detector. Referred to as petalets, these structures are built around a composite sandwich with embedded cooling pipes and electrical tapes for routing the signals and power. Detector modules built using electronic flex boards and silicon strip sensors are glued on both the front and back side surfaces of the carbon structure. Details are given on the assembly, testing and evaluation of several petalets. Measurement results of both mechanical and electrical quantities are shown. Moreover, an outlook is given for improved prototyping plans for large structures.Comment: 22 pages for submission for Journal of Instrumentatio

GRB 170817A-GW170817-AT 2017gfo and the observations of NS-NS, NS-WD and WD-WD mergers

The LIGO-Virgo Collaboration has announced the detection of GW170817 and has associated it with GRB 170817A. These signals have been followed after 11 hours by the optical and infrared emission of AT 2017gfo. The origin of this complex phenomenon has been attributed to a neutron star-neutron star (NS-NS) merger. In order to probe this association we confront our current understanding of the gravitational waves and associated electromagnetic radiation with four observed GRBs originating in binaries composed of different combinations NSs and white dwarfs (WDs). We consider 1) GRB 090510 the prototype of NS-NS merger leading to a black hole (BH); 2) GRB 130603B the prototype of a NS-NS merger leading to massive NS (MNS) with an associated kilonova; 3) GRB 060614 the prototype of a NS-WD merger leading to a MNS with an associated kilonova candidate; 4) GRB 170817A the prototype of a WD-WD merger leading to massive WD with an associated AT 2017gfo-like emission. None of these systems support the above mentioned association. The clear association between GRB 170817A and AT 2017gfo has led to introduce a new model based on on a new subfamily of GRBs originating from WD-WD mergers. We show how this novel model is in agreement with the exceptional observations in the optical, infrared, X- and gamma-rays of GRB 170817A-AT 2017gfo.Comment: version accepted for publication in JCAP. Missing references adde

Quasilocal equilibrium condition for black ring

We use the conservation of the renormalized boundary stress-energy tensor to obtain the equilibrium condition for a general (thin or fat) black ring solution. We also investigate the role of the spatial stress in the thermodynamics of deformation within the quasilocal formalism of Brown and York and discuss the relation with other methods. In particular, we discuss the quantum statistical relation for the unbalanced black ring solution.Comment: v2: refs. added, matches the published versio

Distribuição de Silício em bananeiras inoculadas com Fusarium oxysporum f. sp. Cubense

O mal-do-Panamá, reconhecida como uma das doenças mais destrutivas da bananeira no mundo tem causado enormes prejuízos aos produtores de banana. Dentre as alternativas testadas para o controle de doenças de plantas, encontra-se o uso do silício (Si), que tem apresentado efeitos benéficos em várias espécies, proporcionando efetivo controle de doenças em plantas. O objetivo deste trabalho foi avaliar a resposta da planta, a absorção e translocação de silício em bananeiras inoculadas com Fusarium oxysporum f. sp. cubense. Os tratamentos constaram de 0, 250, 500, 750 e 1000 mg dm-3 de Si, mais um tratamento adicional (testemunha absoluta - sem silício e sem a inoculação com F. oxysporum. f. sp. cubense). O solo em cada vaso foi incubado com Si por 15 dias. Decorrido este período, plantas de bananeira das variedades Grande Naine, Tropical e Maçã, oriundas de cultura de tecidos, foram transferidas para vasos contendo 3 kg de solo. A inoculação com F. oxysporum. procedeu-se 40 dias após o transplantio das plantas para os vasos. Foram determinados a produção da matéria seca da raiz (MSR) e da parte aérea (MSPA), teores de Si na parte aérea e raízes e o índice de translocação. A adição de doses crescentes de Si ao solo elevou a produção da matéria seca da raiz e da parte aérea das plantas de bananeiras. As plantas de bananeiras absorveram e translocaram silício para a parte aérea comportando-se como uma planta acumuladora intermediária de Si