Nonlinear Qubit Transformations

We generalise our previous results of universal linear manipulations [Phys. Rev. A63, 032304 (2001)] to investigate three types of nonlinear qubit transformations using measurement and quantum based schemes. Firstly, nonlinear rotations are studied. We rotate different parts of a Bloch sphere in opposite directions about the z-axis. The second transformation is a map which sends a qubit to its orthogonal state (which we define as ORTHOG). We consider the case when the ORTHOG is applied to only a partial area of a Bloch sphere. We also study nonlinear general transformation, i.e. (theta,phi)->(theta-alpha,phi), again, applied only to part of the Bloch sphere. In order to achieve these three operations, we consider different measurement preparations and derive the optimal average (instead of universal) quantum unitary transformations. We also introduce a simple method for a qubit measurement and its application to other cases.Comment: minor corrections. To appear in PR

Quantum disentanglers

It is not possible to disentangle a qubit in an unknown state $|\psi>$ from a set of (N-1) ancilla qubits prepared in a specific reference state $|0>$. That is, it is not possible to {\em perfectly} perform the transformation $(|\psi,0...,0\r +|0,\psi,...,0\r +...+ |0,0,...\psi\r) \to |0,...,0>\otimes |\psi>$. The question is then how well we can do? We consider a number of different methods of extracting an unknown state from an entangled state formed from that qubit and a set of ancilla qubits in an known state. Measuring the whole system is, as expected, the least effective method. We present various quantum ``devices'' which disentangle the unknown qubit from the set of ancilla qubits. In particular, we present the optimal universal disentangler which disentangles the unknown qubit with the fidelity which does not depend on the state of the qubit, and a probabilistic disentangler which performs the perfect disentangling transformation, but with a probability less than one.Comment: 8 pages, 1 eps figur

Optimal Universal Disentangling Machine for Two Qubit Quantum States

We derive the optimal curve satisfied by the reduction factors, in the case of universal disentangling machine which uses only local operations. Impossibility of constructing a better disentangling machine, by using non-local operations, is discussed.Comment: 15 pages, 2 eps figures, 1 section added, 1 eps figure added, minor corrections, 2 reference numbers correcte

Time and position sensitive single photon detector for scintillator read-out

We have developed a photon counting detector system for combined neutron and gamma radiography which can determine position, time and intensity of a secondary photon flash created by a high-energy particle or photon within a scintillator screen. The system is based on a micro-channel plate photomultiplier concept utilizing image charge coupling to a position- and time-sensitive read-out anode placed outside the vacuum tube in air, aided by a standard photomultiplier and very fast pulse-height analyzing electronics. Due to the low dead time of all system components it can cope with the high throughput demands of a proposed combined fast neutron and dual discrete energy gamma radiography method (FNDDER). We show tests with different types of delay-line read-out anodes and present a novel pulse-height-to-time converter circuit with its potential to discriminate gamma energies for the projected FNDDER devices for an automated cargo container inspection system (ACCIS).Comment: Proceedings of FNDA 201

Growth and Characterization Of Tantulam Selenide

Layered structure (lamellar) solids of transition metal dichalcogenides MX2 (M=Mo,W,Nb,Ta, X=S,Se,Te) have been extensively studied partly because of their excellent lubricating properties and partly due to their photovoltaic properties. Undo extreme pressures fluid lubricants squeeze out from between metting surfaces, causing high friction and wear. With lamellar solids such as TMDCs, shearing takes place more easily when loads are high. So, lamellar solids are well suited to extreme pressure lubrication. As a part of programme of growing than single crystals, this paper presents the growth of TaSe2. The vapour transport technique using iodine as a transporting agent and EDAX and XRD studies gives confirmation also stoichiomatric and structural properties. The type, concentration of charge carriers and also the carrier mobility has been obtained by the Hall effect measurement at room temperature

Steady-State Analysis of Load Balancing with Coxian-22 Distributed Service Times

This paper studies load balancing for many-server ($N$ servers) systems. Each server has a buffer of size $b-1,$ and can have at most one job in service and $b-1$ jobs in the buffer. The service time of a job follows the Coxian-2 distribution. We focus on steady-state performance of load balancing policies in the heavy traffic regime such that the normalized load of system is $\lambda = 1 - N^{-\alpha}$ for $0<\alpha<0.5.$ We identify a set of policies that achieve asymptotic zero waiting. The set of policies include several classical policies such as join-the-shortest-queue (JSQ), join-the-idle-queue (JIQ), idle-one-first (I1F) and power-of-$d$-choices (Po$d$) with $d=O(N^\alpha\log N)$. The proof of the main result is based on Stein's method and state space collapse. A key technical contribution of this paper is the iterative state space collapse approach that leads to a simple generator approximation when applying Stein's method

Costo de capital para el sector vitivin\uedcola Chileno: una propuesta desde el modelo de valoraci\uf3n de activos de capital (CAPM)

The cost of capital is a key input to obtain the fundamental value of an asset or project. In this paper, the cost of capital for the Chilean wine sector was estimated through the Capital Asset Pricing Model (CAPM). We briefly discuss the difficulties that arise when this equilibrium model is used in practice, and the most recent empirical literature dealing with the estimation of the systematic risk coefficient (Beta). From a sample of Chilean wine enterprises, using historical and market information, we found that the cost of capital for the wine sector activities in Chile was of 8.9% per yearin real terms.El costo de capital es un insumo clave para obtener el valor fundamental de un activo o proyecto. En este trabajo se estima el costo de capital del sector vitivin\uedcola chileno a trav\ue9s del Modelo de Valoraci\uf3n de Activos de Capital (CAPM, del ingl\ue9s Capital Asset Pricing Model). Se discuten brevemente las dificultades que emergen al utilizar este modelo de equilibrio en la pr\ue1ctica, y la literatura emp\uedrica reciente sobre la estimaci\uf3n del coeficiente de riesgo sistem\ue1tico (Beta). Basado en una muestra de empresas del sector vitivin\uedcola chileno, e informaci\uf3n hist\uf3rica y de mercado, se encontr\uf3 que el costo de capital asociado al giro vitivin\uedcola en Chile asciende a 8,9% real anual