Constructive control of quantum systems using factorization of unitary operators

We demonstrate how structured decompositions of unitary operators can be employed to derive control schemes for finite-level quantum systems that require only sequences of simple control pulses such as square wave pulses with finite rise and decay times or Gaussian wavepackets. To illustrate the technique it is applied to find control schemes to achieve population transfers for pure-state systems, complete inversions of the ensemble populations for mixed-state systems, create arbitrary superposition states and optimize the ensemble average of dynamic observables.Comment: 28 pages, IoP LaTeX, principal author has moved to Cambridge University ([email protected]

Dietary chia seed (Salvia hispanica L.) rich in a-linolenic acid improves adiposity and normalises hypertriacylglycerolaemia and insulin resistance in dyslipaemic rats

The present study investigates the benefits of the dietary intake of chia seed (Salvia hispanica L.) rich in α-linolenic acid and fibre upon dyslipidaemia and insulin resistance (IR), induced by intake of a sucrose-rich (62.5 %) diet (SRD). To achieve these goals two sets of experiments were designed: (i) to study the prevention of onset of dyslipidaemia and IR in Wistar rats fed during 3 weeks with a SRD in which chia seed was the dietary source of fat; (ii) to analyse the effectiveness of chia seed in improving or reversing the metabolic abnormalities described above. Rats were fed a SRD during 3 months; by the end of this period, stable dyslipidaemia and IR were present in the animals. From months 3-5, half the animals continued with the SRD and the other half were fed a SRD in which the source of fat was substituted by chia seed (SRD+chia). The control group received a diet in which sucrose was replaced by maize starch. The results showed that: (i) dietary chia seed prevented the onset of dyslipidaemia and IR in the rats fed the SRD for 3 weeks - glycaemia did not change; (ii) dyslipidaemia and IR in the long-term SRD-fed rats were normalised without changes in insulinaemia when chia seed provided the dietary fat during the last 2 months of the feeding period. Dietary chia seed reduced the visceral adiposity present in the SRD rats. The present study provides new data regarding the beneficial effect of chia seed upon lipid and glucose homeostasis in an experimental model of dislipidaemia and IR.Fil: Chicco, Adriana Graciela. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Ciencias Biológicas; ArgentinaFil: D'alessandro, Maria Eugenia Guadalupe. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Ciencias Biológicas; ArgentinaFil: Hein, Gustavo Juan. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Ciencias Biológicas; ArgentinaFil: Oliva, Maria Eugenia. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Ciencias Biológicas; ArgentinaFil: Lombardo, Yolanda B.. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Ciencias Biológicas; Argentin

Light-activated modulation and coupling in integrated polymer-liquid crystal systems

We explore the transfer of an incident light pattern onto the liquid crystal (LC) bulk in a photorefractive cell through an integrated photoconducting layer that modulates the electric field applied to the device. The electrical properties and the strength of modulation are investigated as a function of the incident light intensity as well as the frequency and amplitude of the applied voltage, for two LCs with very different electrical conductivity. A simplified electrical model of the cell is proposed, demonstrating that the LC conductivity is a key factor determining the beam-coupling strength

Thermal optical non-linearity of nematic mesophase enhanced by gold nanoparticles – an experimental and numerical investigation

In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n 2 , is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity

The additional-mode garden of RR Lyrae stars

Space-based photometric missions revealed a surprising abundance of millimagnitude-level additional modes in RR Lyrae stars. The modes that appear in the modulated fundamental-mode (RRab) stars can be ordered into four major categories. Here we present the distribution of these groups in the Petersen diagram, and discuss their characteristics and connections to additional modes observed in other RR Lyrae stars.Comment: 4 pages, 4 figures, proceedings of the Joint TASC2-KASC9-SPACEINN-HELAS8 Conference "Seismology of the Sun and the Distant Stars 2016", to be published in EPJ Wo

Design and analysis of high performance phase shifters on polymeric slot waveguides within liquid crystal cladding

We present an on chip phase shifter based on a polymeric slot waveguide and a liquid–crystal cladding, which is capable of reaching high tuning ranges, low control voltages and low propagation losses. Our analysis includes a purely numerical 3D-Finite-Difference-Time-Domain method and a semi-analytical 2D-Finite-Element-Method approach. Both analyses are in agreement, and confirm the high performances. We have used an analytical method in order to study the values of the control voltages, and used electrostatic simulations to validate the approximations. Moreover, in addition to the slot waveguide, we show that it is possible to develop Y-Splitters with negligible values of insertion losses with the same technology, which enables this type of phase shifters to adapt to existing platforms of polymeric optical integrated circuits, significantly enhancing their modulation capabilities

Degrees of controllability for quantum systems and applications to atomic systems

Precise definitions for different degrees of controllability for quantum systems are given, and necessary and sufficient conditions are discussed. The results are applied to determine the degree of controllability for various atomic systems with degenerate energy levels and transition frequencies.Comment: 20 pages, IoP LaTeX, revised and expanded versio

Avalanche dynamics of radio pulsar glitches

We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organised critical state. Analysis of the glitch population (currently 285 events from 101 pulsars) demonstrates that the size distribution in individual pulsars is consistent with being scale invariant, as expected for an avalanche process. The waiting-time distribution is consistent with being exponential in seven out of nine pulsars where it can be measured reliably, after adjusting for observational limits on the minimum waiting time, as for a constant-rate Poisson process. PSR J0537$-$6910 and PSR J0835$-$4510 are the exceptions; their waiting-time distributions show evidence of quasiperiodicity. In each object, stationarity requires that the rate $\lambda$ equals $- \epsilon \dot{\nu} /$, where $\dot{\nu}$ is the angular acceleration of the crust, $$ is the mean glitch size, and $\epsilon\dot{\nu}$ is the relative angular acceleration of the crust and superfluid. There is no evidence that $\lambda$ changes monotonically with spin-down age. The rate distribution itself is fitted reasonably well by an exponential for $\lambda \geq 0.25 {\rm yr^{-1}}$. For $\lambda < 0.25 {\rm yr^{-1}}$, its exact form is unknown; the exponential overestimates the number of glitching pulsars observed at low $\lambda$, where the limited total observation time exercises a selection bias.Comment: Accepted for publication in the Astrophysical Journa

Impact of positivity and complete positivity on accessibility of Markovian dynamics

We consider a two-dimensional quantum control system evolving under an entropy-increasing irreversible dynamics in the semigroup form. Considering a phenomenological approach to the dynamics, we show that the accessibility property of the system depends on whether its evolution is assumed to be positive or completely positive. In particular, we characterize the family of maps having different accessibility and show the impact of that property on observable quantities by means of a simple physical model.Comment: 11 pages, to appear in J. Phys.

Implementing Quantum Gates using the Ferromagnetic Spin-J XXZ Chain with Kink Boundary Conditions

We demonstrate an implementation scheme for constructing quantum gates using unitary evolutions of the one-dimensional spin-J ferromagnetic XXZ chain. We present numerical results based on simulations of the chain using the time-dependent DMRG method and techniques from optimal control theory. Using only a few control parameters, we find that it is possible to implement one- and two-qubit gates on a system of spin-3/2 XXZ chains, such as Not, Hadamard, Pi-8, Phase, and C-Not, with fidelity levels exceeding 99%.Comment: Updated Acknowledgement