A simple spectral condition implying separability for states of bipartite quantum systems

For two qubits and for general bipartite quantum systems, we give a simple spectral condition in terms of the ordered eigenvalues of the density matrix which guarantees that the corresponding state is separable.Comment: 5 pages Revised 31 May 200

Symmetry implies independence

Given a quantum system consisting of many parts, we show that symmetry of the system's state, i.e., invariance under swappings of the subsystems, implies that almost all of its parts are virtually identical and independent of each other. This result generalises de Finetti's classical representation theorem for infinitely exchangeable sequences of random variables as well as its quantum-mechanical analogue. It has applications in various areas of physics as well as information theory and cryptography. For example, in experimental physics, one typically collects data by running a certain experiment many times, assuming that the individual runs are mutually independent. Our result can be used to justify this assumption.Comment: LaTeX, contains 4 figure

Monogamy of entanglement and other correlations

It has been observed by numerous authors that a quantum system being entangled with another one limits its possible entanglement with a third system: this has been dubbed the "monogamous nature of entanglement". In this paper we present a simple identity which captures the trade-off between entanglement and classical correlation, which can be used to derive rigorous monogamy relations. We also prove various other trade-offs of a monogamy nature for other entanglement measures and secret and total correlation measures.Comment: 7 pages, revtex

One-and-a-half quantum de Finetti theorems

We prove a new kind of quantum de Finetti theorem for representations of the unitary group U(d). Consider a pure state that lies in the irreducible representation U_{mu+nu} for Young diagrams mu and nu. U_{mu+nu} is contained in the tensor product of U_mu and U_nu; let xi be the state obtained by tracing out U_nu. We show that xi is close to a convex combination of states Uv, where U is in U(d) and v is the highest weight vector in U_mu. When U_{mu+nu} is the symmetric representation, this yields the conventional quantum de Finetti theorem for symmetric states, and our method of proof gives near-optimal bounds for the approximation of xi by a convex combination of product states. For the class of symmetric Werner states, we give a second de Finetti-style theorem (our 'half' theorem); the de Finetti-approximation in this case takes a particularly simple form, involving only product states with a fixed spectrum. Our proof uses purely group theoretic methods, and makes a link with the shifted Schur functions. It also provides some useful examples, and gives some insight into the structure of the set of convex combinations of product states.Comment: 14 pages, 3 figures, v4: minor additions (including figures), published versio

Continuity and Stability of Partial Entropic Sums

Extensions of Fannes' inequality with partial sums of the Tsallis entropy are obtained for both the classical and quantum cases. The definition of kth partial sum under the prescribed order of terms is given. Basic properties of introduced entropic measures and some applications are discussed. The derived estimates provide a complete characterization of the continuity and stability properties in the refined scale. The results are also reformulated in terms of Uhlmann's partial fidelities.Comment: 9 pages, no figures. Some explanatory and technical improvements are made. The bibliography is extended. Detected errors and typos are correcte

Proyecto IRESUD: interconexión de sistemas fotovoltaicos a la red eléctrica en ambientes urbanos. estado de avance a julio de 2014 y primeras mediciones en sistemas piloto

En el marco de una convocatoria del Ministerio de Ciencia, Tecnología e Innovación Productiva, se conformó, en el año 2011, el consorcio público-privado IRESUD entre la Comisión Nacional de Energía Atómica (CNEA), la Universidad Nacional de San Martín (UNSAM) y 5 empresas privadas, para la ejecución del proyecto “Interconexión de Sistemas Fotovoltaicos a la Red Eléctrica en Ambientes Urbanos”. El principal objetivo del mismo es introducir en el país tecnologías asociadas con la interconexión a la red eléctrica, en áreas urbanas, de sistemas fotovoltaicos (FV), contemplando para ello cuestiones técnicas, económicas y regulatorias. En este trabajo, se presenta el grado de avance del proyecto en lo referente a las cuestiones regulatorias y a las instalaciones piloto realizadas o en ejecución en diferentes partes del país. Asimismo, se muestran las primeras mediciones de algunas de las instalaciones actualmente en operación y se analiza el comportamiento de un inversor FV de conexión a red.Fil: Durán, J. C.. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín; ArgentinaFil: Socolovsky, Hernan Pablo. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín; ArgentinaFil: Raggio, D.. Comisión Nacional de Energía Atómica; ArgentinaFil: Godfrin, Elena María. Comisión Nacional de Energía Atómica; ArgentinaFil: Jakimczyk, J.. Universidad Tecnológica Nacional; ArgentinaFil: Martinez Bogado, Mónica Gladys. Universidad Nacional de San Martín; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Diaz, F. J.. Universidad Nacional de La Plata. Facultad de Informática; ArgentinaFil: Castro, N. E.. Universidad Nacional de La Plata. Facultad de Informática; ArgentinaFil: Pedro, G.. Provincia del Neuquen. Ministerio de Hacienda Obras y Servivcios Publicos. Ente Provincial de Energia del Neuquen; ArgentinaFil: Sepúlveda, O.. Provincia del Neuquen. Ministerio de Hacienda Obras y Servivcios Publicos. Ente Provincial de Energia del Neuquen; ArgentinaFil: Argañaraz, C.. Provincia del Neuquen. Ministerio de Hacienda Obras y Servivcios Publicos. Ente Provincial de Energia del Neuquen; ArgentinaFil: Benítez, E.. Universidad Nacional de Luján; ArgentinaFil: Roldán, A.. Universidad Nacional de Luján; ArgentinaFil: Righini, R.. Universidad Nacional de Luján; Argentin

Blow-up profile of rotating 2D focusing Bose gases

We consider the Gross-Pitaevskii equation describing an attractive Bose gas trapped to a quasi 2D layer by means of a purely harmonic potential, and which rotates at a fixed speed of rotation $\Omega$. First we study the behavior of the ground state when the coupling constant approaches $a\_*$ , the critical strength of the cubic nonlinearity for the focusing nonlinear Schr{\"o}dinger equation. We prove that blow-up always happens at the center of the trap, with the blow-up profile given by the Gagliardo-Nirenberg solution. In particular, the blow-up scenario is independent of $\Omega$, to leading order. This generalizes results obtained by Guo and Seiringer (Lett. Math. Phys., 2014, vol. 104, p. 141--156) in the non-rotating case. In a second part we consider the many-particle Hamiltonian for $N$ bosons, interacting with a potential rescaled in the mean-field manner $--a\_N N^{2\beta--1} w(N^{\beta} x), with$w$a positive function such that$\int\_{\mathbb{R}^2} w(x) dx = 1$. Assuming that$\beta < 1/2$and that$a\_N \to a\_*$sufficiently slowly, we prove that the many-body system is fully condensed on the Gross-Pitaevskii ground state in the limit$N \to \infty$

Adversarial hypothesis testing and a quantum stein's lemma for restricted measurements

Recall the classical hypothesis testing setting with two convex sets of probability distributions P and Q. One receives either n i.i.d. samples from a distribution p ∈ P or from a distribution q ∈ Q and wants to decide from which set the points were sampled. It is known that the optimal exponential rate at which errors decrease can be achieved by a simple maximum-likelihood ratio test which does not depend on p or q, but only on the sets P and Q. We consider an adaptive generalization of this model where the choice of p ∈ P and q ∈ Q can change in each sample in some way that depends arbitrarily on the previous samples. In other words, in the kth round, an adversary, having observed all the previous samples in rounds 1, ..., κ-1, chooses p[subscript κ] ∈ P and q[subscript κ] ∈ Q, with the goal of confusing the hypothesis test. We prove that even in this case, the optimal exponential error rate can be achieved by a simple maximum-likelihood test that depends only on P and Q. We then show that the adversarial model has applications in hypothesis testing for quantum states using restricted measurements. For example, it can be used to study the problem of distinguishing entangled states from the set of all separable states using only measurements that can be implemented with local operations and classical communication (LOCC). The basic idea is that in our setup, the deleterious effects of entanglement can be simulated by an adaptive classical adversary. We prove a quantum Stein's Lemma in this setting: In many circumstances, the optimal hypothesis testing rate is equal to an appropriate notion of quantum relative entropy between two states. In particular, our arguments yield an alternate proof of Li and Winter's recent strengthening of strong subadditivity for quantum relative entropy.National Science Foundation (U.S.) (Grant CCF-1111382)United States. Army Research Office (Contract W911NF-12-1-0486

Faithful Squashed Entanglement

Squashed entanglement is a measure for the entanglement of bipartite quantum states. In this paper we present a lower bound for squashed entanglement in terms of a distance to the set of separable states. This implies that squashed entanglement is faithful, that is, strictly positive if and only if the state is entangled. We derive the bound on squashed entanglement from a bound on quantum conditional mutual information, which is used to define squashed entanglement and corresponds to the amount by which strong subadditivity of von Neumann entropy fails to be saturated. Our result therefore sheds light on the structure of states that almost satisfy strong subadditivity with equality. The proof is based on two recent results from quantum information theory: the operational interpretation of the quantum mutual information as the optimal rate for state redistribution and the interpretation of the regularised relative entropy of entanglement as an error exponent in hypothesis testing. The distance to the set of separable states is measured by the one-way LOCC norm, an operationally-motivated norm giving the optimal probability of distinguishing two bipartite quantum states, each shared by two parties, using any protocol formed by local quantum operations and one-directional classical communication between the parties. A similar result for the Frobenius or Euclidean norm follows immediately. The result has two applications in complexity theory. The first is a quasipolynomial-time algorithm solving the weak membership problem for the set of separable states in one-way LOCC or Euclidean norm. The second concerns quantum Merlin-Arthur games. Here we show that multiple provers are not more powerful than a single prover when the verifier is restricted to one-way LOCC operations thereby providing a new characterisation of the complexity class QMA.Comment: 24 pages, 1 figure, 1 table. Due to an error in the published version, claims have been weakened from the LOCC norm to the one-way LOCC nor

Depressive and anxiety symptoms screening in cardiac inpatients : a virtuous italian approach to psychocardiology

Despite the fact that American Heart Association (AHA) recommended a systematic screening for depression in cardiovascular inpatients, poor attention has been given to this issue. Furthermore, no specific guidelines exist for anxiety screening in cardiovascular inpatients. Thus, the aims of this study were to verify the feasibility of a depressive and anxiety symptoms screening protocol in an Italian hospital specializing in cardiovascular diseases and to evaluate both anxiety and depressive symptoms prevalence. A group of 2009 consecutive inpatients completed the 9-item Patient Health Questionnaire (PHQ-9) and the 7-item Generalized Anxiety Disorder (GAD-7). The rates of depressive and anxiety symptoms were almost 9% and 16% respectively. Men were less likely than women to experience both depressive and anxiety symptoms. Patients who were admitted to the heart failure unit reported higher risk of experiencing both symptoms compared to patients in other wards. Similarly, patients admitted to the cardiac surgery unit showed a higher risk of experiencing anxiety symptoms compared to other patients. The proposed screening procedure showed a good feasibility and acceptance. This study highlighted the importance of implementing a short screening procedure in hospitals dealing with cardiovascular inpatients to identify those individuals who require specific attention and interventions