Measuring work and heat in ultracold quantum gases

We propose a feasible experimental scheme to direct measure heat and work in cold atomic setups. The method is based on a recent proposal which shows that work is a positive operator valued measure (POVM). In the present contribution, we demonstrate that the interaction between the atoms and the light polarisation of a probe laser allows us to implement such POVM. In this way the work done on or extracted from the atoms after a given process is encoded in the light quadrature that can be measured with a standard homodyne detection. The protocol allows one to verify fluctuation theorems and study properties of the non-unitary dynamics of a given thermodynamic process.Comment: Published version in the Focus Issue on "Quantum Thermodynamics

Comment on "General Non-Markovian Dynamics of Open Quantum Systems"

The existence of a "non-Markovian dissipationless" regime, characterized by long lived oscillations, was recently reported for a class of quantum open systems (Zhang et al, PRL, 109, 170402, (2012)). It is claimed this could happen in the strong coupling regime, a surprising result which has attracted some attention. We show that this regime exists if and only if the total Hamiltonian is unbounded from below, casting serious doubts on the usefulness of this result

Spin Chains in an External Magnetic Field. Closure of the Haldane Gap and Effective Field Theories

We investigate both numerically and analytically the behaviour of a spin-1 antiferromagnetic (AFM) isotropic Heisenberg chain in an external magnetic field. Extensive DMRG studies of chains up to N=80 sites extend previous analyses and exhibit the well known phenomenon of the closure of the Haldane gap at a lower critical field H_c1. We obtain an estimate of the gap below H_c1. Above the lower critical field, when the correlation functions exhibit algebraic decay, we obtain the critical exponent as a function of the net magnetization as well as the magnetization curve up to the saturation (upper critical) field H_c2. We argue that, despite the fact that the SO(3) symmetry of the model is explicitly broken by the field, the Haldane phase of the model is still well described by an SO(3) nonlinear sigma-model. A mean-field theory is developed for the latter and its predictions are compared with those of the numerical analysis and with the existing literature.Comment: 11 pages, 4 eps figure

Redundancy of classical and quantum correlations during decoherence

We analyze the time dependence of entanglement and total correlations between a system and fractions of its environment in the course of decoherence. For the quantum Brownian motion model we show that the entanglement and total correlations have rather different dependence on the size of the environmental fraction. Redundancy manifests differently in both types of correlations and can be related with induced--classicality. To study this we introduce a new measure of redundancy and compare it with the existing one.Comment: 6 pages, 4 figure

Using Gene Ontology to describe the role of the neurexin-neuroligin-SHANK complex in human, mouse and rat and its relevance to autism

People with an autistic spectrum disorder (ASD) display a variety of characteristic behavioral traits, including impaired social interaction, communication difficulties and repetitive behavior. This complex neurodevelopment disorder is known to be associated with a combination of genetic and environmental factors. Neurexins and neuroligins play a key role in synaptogenesis and neurexin-neuroligin adhesion is one of several processes that have been implicated in autism spectrum disorders

Qubits in phase space: Wigner function approach to quantum error correction and the mean king problem

We analyze and further develop a new method to represent the quantum state of a system of $n$ qubits in a phase space grid of $N\times N$ points (where $N=2^n$). The method, which was recently proposed by Wootters and co--workers (Gibbons {\it et al.}, quant-ph/0401155), is based on the use of the elements of the finite field $GF(2^n)$ to label the phase space axes. We present a self--contained overview of the method, we give new insights on some of its features and we apply it to investigate problems which are of interest for quantum information theory: We analyze the phase space representation of stabilizer states and quantum error correction codes and present a phase space solution to the so--called ``mean king problem''.Comment: 18 pages, 16 figures; typos fixed, some minor corrections, figures of the circuits were change

Finding critical points using improved scaling Ansaetze

Analyzing in detail the first corrections to the scaling hypothesis, we develop accelerated methods for the determination of critical points from finite size data. The output of these procedures are sequences of pseudo-critical points which rapidly converge towards the true critical points. In fact more rapidly than previously existing methods like the Phenomenological Renormalization Group approach. Our methods are valid in any spatial dimensionality and both for quantum or classical statistical systems. Having at disposal fast converging sequences, allows to draw conclusions on the basis of shorter system sizes, and can be extremely important in particularly hard cases like two-dimensional quantum systems with frustrations or when the sign problem occurs. We test the effectiveness of our methods both analytically on the basis of the one-dimensional XY model, and numerically at phase transitions occurring in non integrable spin models. In particular, we show how a new Homogeneity Condition Method is able to locate the onset of the Berezinskii-Kosterlitz-Thouless transition making only use of ground-state quantities on relatively small systems.Comment: 16 pages, 4 figures. New version including more general Ansaetze basically applicable to all case

Long-distance entanglement in spin systems

Most quantum system with short-ranged interactions show a fast decay of entanglement with the distance. In this Letter, we focus on the peculiarity of some systems to distribute entanglement between distant parties. Even in realistic models, like the spin-1 Heisenberg chain, sizable entanglement is present between arbitrarily distant particles. We show that long distance entanglement appears for values of the microscopic parameters which do not coincide with known quantum critical points, hence signaling a transition detected only by genuine quantum correlations.Comment: RevTex, 5 pages, 7 .eps figures Two references added in published versio

Charmed Baryons with J=3/2J = 3/2

The width of a recently discovered excited charmed-strange baryon, a candidate for a state $\Xi_c^*$ with spin 3/2, is calculated. In the absence of configuration mixing between the ground-state (spin-1/2) charmed-strange baryon $\Xi_c^{(a)}$ and the spin-1/2 state $\Xi_c^{(s)}$ lying about 95 MeV above it, one finds $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = (3/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$ and $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(s)} \pi) = (1/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$, where the tilde denotes the partial width with kinematic factors removed. Assuming a kinematic factor for P-wave decay of $p_{\rm cm}^3$, one predicts $\Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = 2.3$ MeV, while the $\Xi^*_c \to \Xi_c^{(s)} \pi$ channel is closed. Some suggestions are given for detecting the $\Sigma_c^*$, the spin-3/2 charmed nonstrange baryon, and the $\Omega_c^*$, the spin-3/2 charmed doubly-strange baryon.Comment: 11 pages, latex, 2 uuencoded figures sent separatel

A transcriptome analysis identifies molecular effectors of unconjugated bilirubin in human neuroblastoma SH-SY5Y cells

Background: The deposition of unconjugated bilirubin (UCB) in selected regions of the brain results in irreversible neuronal damage, or Bilirubin Encephalopathy (BE). Although UCB impairs a large number of cellular functions in other tissues, the basic mechanisms of neurotoxicity have not yet been fully clarified. While cells can accumulate UCB by passive diffusion, cell protection may involve multiple mechanisms including the extrusion of the pigment as well as pro-survival homeostatic responses that are still unknown. Results: Transcriptome changes induced by UCB exposure in SH-SY5Y neuroblastoma cell line were examined by high density oligonucleotide microarrays. Two-hundred and thirty genes were induced after 24 hours. A Gene Ontology (GO) analysis showed that at least 50 genes were directly involved in the endoplasmic reticulum (ER) stress response. Validation of selected ER stress genes is shown by quantitative RT-PCR. Analysis of XBP1 splicing and DDIT3/CHOP subcellular localization is presented. Conclusion: These results show for the first time that UCB exposure induces ER stress response as major intracellular homeostasis in surviving neuroblastoma cells in vitro