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

X-ray redshifts with the International X-ray Observatory (IXO)

7 páginas, 4 figuras, 1 tabla.-- El pdf del artículo es la versión pre-print.We explore the capabilities of the future space science mission IXO (International X-ray Observatory) for obtaining cosmological redshifts of distant Active Galactic Nuclei (AGNs) using the X-ray data only. We first find in which regions of the X-ray luminosity (LX) versus redshift (z) plane the weak but ubiquitous Fe Ka narrow emission line can deliver an accurate redshift (dz < 5%) as a function of exposure time, using a CCD-based Wide Field Imager (IXO/WFI) as the one baselined for IXO. Down to a 2–10 keV X-ray flux of 10-14 erg cm-2 s-1 IXO/WFI exposures of 100 ks, 300 ks and 1Ms will deliver 20%, 40% and 60% of the redshifts. This means that in a typical 18' - 18' IXO/WFI field of view, 4, 10 and 25 redshifts will be obtained for free from the X-ray data alone, spanning a wide range up to z - 2–3 and fairly sampling the real distribution. Measuring redshifts of fainter sources will indeed need spectroscopy at other wavebands.We acknowledge partial financial support from the Spanish Ministerio de Ciencia e Innovación project AYA2009-08059. N. Castelló thanks the Spanish Ministerio de Ciencia e Innovación for a pre-doctoral fellowship.Peer reviewe

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

Realization of Optimal Disentanglement by Teleportation via Separable Channel

We discuss here the best disentanglement processes of states of two two-level systems which belong to (i) the universal set, (ii) the set in which the states of one party lie on a single great circle of the Bloch sphere, and (iii) the set in which the states of one party commute with each other, by teleporting the states of one party (on which the disentangling machine is acting) through three particular type of separable channels, each of which is a mixture of Bell states. In the general scenario, by teleporting one party's state of an arbitrary entangled state of two two-level parties through some mixture of Bell states, we have shown that this entangled state can be made separable by using a physically realizable map $\tilde{V}$, acting on one party's states, if $\tilde{V} (I) = I, \tilde{V} ({\sigma}_j) = {\lambda}_j {\sigma}_j$, where ${\lambda}_j \ge 0$ (for $j = 1, 2, 3$), and ${\lambda}_1 + {\lambda}_2 + {\lambda}_3 \le 1$.Comment: 20 pages Late

Laboratorio m?vil al alcance en el ?rea de ciencias naturales y educaci?n ambiental con los estudiantes del ciclo II del colegio andino San Nicolas

90 p. Recurso Electr?nicoEl proyecto laboratorio m?vil al alcance promueve el aprendizaje significativo de las clases de ciencias naturales, su principal objetivo es brindar al educando herramientas que le permitan tener un ?ptimo aprendizaje. Para definir su estructura y objetivos se realizaron observaciones en el colegio Andino San Nicol?s, ubicado al suroccidente del municipio de Soacha (Cundinamarca), comuna 1. Durante la ejecuci?n de clases de ciencias naturales se evidencio la realizaci?n de clases tradicionales, identificando la necesidad de implementar una herramienta l?dica, un laboratorio que pueda ser trasladado. Para dar respuesta a la pregunta problema, se estableci? que el tipo de investigaci?n en la cual se basara el proyecto es el I.A.P (investigaci?n por acci?n participativa) que permite la interacci?n de dos procesos, el de conocer y el de actuar. Se dise?ara un manual de laboratorio para la utilizaci?n adecuada de los recursos, en este caso m?vil, se dise?a e implementa con una cartilla que explica cada experimento propuesto, interactuando con tres personajes llamados: Paola, Andrea y Luis, autores del proyecto. En los estudiantes el Laboratorio gener? sorpresa y curiosidad su dise?o m?vil les hizo preguntarse: ?Qu? era la caja en forma de casa?, ?Por qu? un laboratorio m?vil?, ?Qu? hay dentro de la caja en forma de casa?; les asombro el uso de materiales comunes que suelen desecharse , con estos se realiza una clase l?dica, la cartilla y sus personajes despertaron su esp?ritu cient?fico, permitiendo el cumplimiento del objetivo del proyecto. Palabras clave: laboratorio m?vil, aprendizaje significativo, I.A.P, din?mica, l?dica.The mobile accessible laboratory project promotes meaningful learning of natural science classes, its main objective is to provide the learner with tools that allow him to have an optimal learning. In order to define its structure and objectives, observations were made at Andino San Nicolas College, located at the southwest of the municipality of Soacha (Cundinamarca), commune 1. During the execution of natural science classes, the realization of traditional classes was evidenced, identifying the need to implement a playful tool, a laboratory that can be transferred. In order to answer the problem question, it was established that the type of research on which the project was based is the I.A.P (participatory action research) that allows the interaction of two processes, that of knowing and acting. A laboratory manual will be designed for the proper use of resources, in this mobile case, it is designed and implemented with a primer explaining each experiment proposed, interacting with three characters called: Paola, Andrea and Luis, authors of the project. In the students the Laboratory generated surprise and curiosity, their mobile design made them wonder: What was the box in the form of a house?, Why a mobile laboratory?, What is inside the box in the form of a house?; I am amazed at the use of common materials that are often discarded, with these a playful class is done, the primer and its characters awakened their scientific spirit, allowing the fulfillment of the project objective. Keywords: mobile laboratory, meaningful learning, I.A.P, dynamic, play

Design approaches in technology enhanced learning

Design is a critical to the successful development of any interactive learning environment (ILE). Moreover, in technology enhanced learning (TEL), the design process requires input from many diverse areas of expertise. As such, anyone undertaking tool development is required to directly address the design challenge from multiple perspectives. We provide a motivation and rationale for design approaches for learning technologies that draws upon Simon's seminal proposition of Design Science (Simon, 1969). We then review the application of Design Experiments (Brown, 1992) and Design Patterns (Alexander et al., 1977) and argue that a patterns approach has the potential to address many of the critical challenges faced by learning technologists

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

Finite lifetime eigenfunctions of coupled systems of harmonic oscillators

We find a Hermite-type basis for which the eigenvalue problem associated to the operator $H_{A,B}:=B(-\partial_x^2)+Ax^2$ acting on $L^2({\bf R};{\bf C}^2)$ becomes a three-terms recurrence. Here $A$ and $B$ are two constant positive definite matrices with no other restriction. Our main result provides an explicit characterization of the eigenvectors of $H_{A,B}$ that lie in the span of the first four elements of this basis when $AB\not= BA$.Comment: 11 pages, 1 figure. Some typos where corrected in this new versio