Estimation of Spin-Spin Interaction by Weak Measurement Scheme

Precisely knowing an interaction Hamiltonian is crucial to realize quantum information tasks, especially to experimentally demonstrate a quantum computer and a quantum memory. We propose a scheme to experimentally evaluate the spin-spin interaction for a two-qubit system by the weak measurement technique initiated by Yakir Aharonov and his colleagues. Furthermore, we numerically confirm our proposed scheme in a specific system of a nitrogen vacancy center in diamond. This means that the weak measurement can also be taken as a concrete example of the quantum process tomography.Comment: 4 pages, 1 table, 2 figures, to appear in Europhysics Letter

Advantages of nonclassical pointer states in postselected weak measurements

We investigate, within the weak measurement theory, the advantages of non-classical pointer states over semi-classical ones for coherent, squeezed vacuum, and Schr\"{o}inger cat states. These states are utilized as pointer state for the system operator $\hat{A}$ with property $\hat{A}^{2}=\hat{I}$, where $\hat{I}$ represents the identity operator. We calculate the ratio between the signal-to-noise ratio (SNR) of non-postselected and postselected weak measurements. The latter is used to find the quantum Fisher information for the above pointer states. The average shifts for those pointer states with arbitrary interaction strength are investigated in detail. One key result is that we find the postselected weak measurement scheme for non-classical pointer states to be superior to semi-classical ones. This can improve the precision of measurement process.Comment: 8 pages, 5 figure

Asymptotic entanglement in 1D quantum walks with a time-dependent coined

Discrete-time quantum walk evolve by a unitary operator which involves two operators a conditional shift in position space and a coin operator. This operator entangles the coin and position degrees of freedom of the walker. In this paper, we investigate the asymptotic behavior of the coin position entanglement (CPE) for an inhomogeneous quantum walk which determined by two orthogonal matrices in one-dimensional lattice. Free parameters of coin operator together provide many conditions under which a measurement perform on the coin state yield the value of entanglement on the resulting position quantum state. We study the problem analytically for all values that two free parameters of coin operator can take and the conditions under which entanglement becomes maximal are sought.Comment: 23 pages, 4 figures, accepted for publication in IJMPB. arXiv admin note: text overlap with arXiv:1001.5326 by other author

Genetic differentiation, effective population size and gene flow in marine fishes : implications for stock management

Many commercially exploited marine fish and mollusc species exhibit no or a low degree of genetic differentiation in neutral marker genes. This lack of genetic differentiation, typically attributed to high degree of gene flow in marine environments, has sometimes supported the thinking that genetically indistinguishable stocks can be managed as being one panmictic population. Recent comparative studies of neutral marker gene and quantitative trait differentiation in a wide variety of taxa - including several marine organisms - show that a high degree of genetic differentiation (as measured by Q_) in ecologically and economically important traits is a common place occurrence, even when the degree of differentiation in neutral marker genes (as measured by F_) is low or absent. In fact, among the empirical studies made so far, the outcome Q_>F_ is pervasive. This accords with the increasing evidence that natal homing and self-replenishment of local populations may be more common in marine habitats than previously anticipated. If so, the low degree of genetic differentiation in neutral genetic markers could be a simple consequence of the large effective population size (N_e) of many marine populations, effectively buffering them against differentiation due to genetic drift. However, genetic markers linked to parts of the genome under directional selection should readily diverge in allele frequencies especially when N_e is high. In fact, several recent studies have discovered that such loci provide a way to differentiate among stocks undifferentiated in neutral marker genes. Hence, the study of adaptive rather than neutral genetic differentiation among fish and shellfish populations might provide practical tools for stock identification and thereby contribute to improved fisheries policies.Special Revie

Plant genotype and induced defenses affect the productivity of an insect-killing obligate viral pathogen

© 2017 Elsevier Inc. Plant-mediated variations in the outcomes of host-pathogen interactions can strongly affect epizootics and the population dynamics of numerous species, including devastating agricultural pests such as the fall armyworm. Most studies of plant-mediated effects on insect pathogens focus on host mortality, but few have measured pathogen yield, which can affect whether or not an epizootic outbreak occurs. Insects challenged with baculoviruses on different plant species and parts can vary in levels of mortality and yield of infectious stages (occlusion bodies; OBs). We previously demonstrated that soybean genotypes and induced anti-herbivore defenses influence baculovirus infectivity. Here, we used a soybean genotype that strongly reduced baculovirus infectivity when virus was ingested on induced plants (Braxton) and another that did not reduce infectivity (Gasoy), to determine how soybean genotype and induced defenses influence OB yield and speed of kill. These are key fitness measures because baculoviruses are obligate-killing pathogens. We challenged fall armyworm, Spodoptera frugiperda, with the baculovirus S. frugiperda multi-nucleocapsid nucleopolyhedrovirus (SfMNPV) during short or long-term exposure to plant treatments (i.e., induced or non-induced genotypes). Caterpillars were either fed plant treatments only during virus ingestion (short-term exposure to foliage) or from the point of virus ingestion until death (long-term exposure). We found trade-offs of increasing OB yield with slower speed of kill and decreasing virus dose. OB yield increased more with longer time to death and decreased more with increasing virus dose after short-term feeding on Braxton compared with Gasoy. OB yield increased significantly more with time to death in larvae that fed until death on non-induced foliage than induced foliage. Moreover, fewer OBs per unit of host tissue were produced when larvae were fed induced foliage than non-induced foliage. These findings highlight the potential importance of plant effects, even at the individual plant level, on entomopathogen fitness, which may impact epizootic transmission events and host population dynamics

Study on Photon Activation Analysis of Carbon in Glasses for Fiber Amplifiers by Using the Flow Method for the Rapid Separation of ^<11>C(II. Radiochemistry)

We have studied nuclear interference from a matrix produced by (γ, n), (γ, 2n), (γ, p) and (n, γ) reactions and a flow method for ^C separation in order to develop an approach for the photon activation analysis of carbon in InF_3-based fluoride, chalcogenide and tellurite glasses for fiber amplifiers. We found that seventeen radionuclides are produced from these glasses and chemical separation is necessary to determine carbon. For the flow method, which involves the fusion of an irradiated sample with an oxidizer, the conversion of ^C into ^CO_2, and the absorption of ^C in ethanolamine solution, we used a mixture of Pb_3O_4 and B_2O_3 as the oxidizer. We also found that the reaction between ^F(γ, n) and ^Na(γ, αn) in the ethanolamine solution produced ^F contamination with fluoride and chalcogenide glasses and that this flow method can only be applied to tellurite glasses. We confirmed that the chemical yield of the flow method was close to 100 % when determining carbon in standard steel samples by using lithium carbonate as a standard sample. We determined that the carbon concentrations in two kinds of tellurite glass were 8 to 13 and 21 to 28 ppm, respectively

Optimal Covariant Measurement of Momentum on a Half Line in Quantum Mechanics

We cannot perform the projective measurement of a momentum on a half line since it is not an observable. Nevertheless, we would like to obtain some physical information of the momentum on a half line. We define an optimality for measurement as minimizing the variance between an inferred outcome of the measured system before a measuring process and a measurement outcome of the probe system after the measuring process, restricting our attention to the covariant measurement studied by Holevo. Extending the domain of the momentum operator on a half line by introducing a two dimensional Hilbert space to be tensored, we make it self-adjoint and explicitly construct a model Hamiltonian for the measured and probe systems. By taking the partial trace over the newly introduced Hilbert space, the optimal covariant positive operator valued measure (POVM) of a momentum on a half line is reproduced. We physically describe the measuring process to optimally evaluate the momentum of a particle on a half line.Comment: 12 pages, 3 figure

Post-Hartree-Fock method in Quantum Chemistry for Quantum Computer

Quantum computational chemistry is a potential application of quantum computers that is expected to effectively solve several quantum-chemistry problems, particularly the electronic structure problem. Quantum computational chemistry can be compared to the conventional computational devices. This review comprehensively investigates the applications and overview of quantum computational chemistry, including a review of the Hartree-Fock method for quantum information scientists. Quantum algorithms, quantum phase estimation, and variational quantum eigensolver, have been applied to the post-Hartree-Fock method.Comment: 31 pages, 6 figure

Quantification of concurrence via weak measurement

Since entanglement is not an observable per se, measuring its value in practice is a difficult task. Here we propose a protocol for quantifying a particular entanglement measure, namely, concurrence, of an arbitrary two-qubit pure state via a single fixed measurement setup by exploiting so-called weak measurements and the associated weak values together with the properties of the Laguerre-Gaussian modes. The virtue of our technique is that it is generally applicable for all two-qubit systems and does not involve simultaneous copies of the entangled state. We also propose an explicit optical implementation of the protocol

Closed timelike curves via post-selection: theory and experimental demonstration

Closed timelike curves (CTCs) are trajectories in spacetime that effectively travel backwards in time: a test particle following a CTC can in principle interact with its former self in the past. CTCs appear in many solutions of Einstein's field equations and any future quantum version of general relativity will have to reconcile them with the requirements of quantum mechanics and of quantum field theory. A widely accepted quantum theory of CTCs was proposed by Deutsch. Here we explore an alternative quantum formulation of CTCs and show that it is physically inequivalent to Deutsch's. Because it is based on combining quantum teleportation with post-selection, the predictions/retrodictions of our theory are experimentally testable: we report the results of an experiment demonstrating our theory's resolution of the well-known `grandfather paradox.Comment: 5 pages, 4 figure