The entanglement of few-particle systems when using the local-density approximation

In this chapter we discuss methods to calculate the entanglement of a system using density-functional theory. We firstly introduce density-functional theory and the local-density approximation (LDA). We then discuss the concept of the `interacting LDA system'. This is characterised by an interacting many-body Hamiltonian which reproduces, uniquely and exactly, the ground state density obtained from the single-particle Kohn-Sham equations of density-functional theory when the local-density approximation is used. We motivate why this idea can be useful for appraising the local-density approximation in many-body physics particularly with regards to entanglement and related quantum information applications. Using an iterative scheme, we find the Hamiltonian characterising the interacting LDA system in relation to the test systems of Hooke's atom and helium-like atoms. The interacting LDA system ground state wavefunction is then used to calculate the spatial entanglement and the results are compared and contrasted with the exact entanglement for the two test systems. For Hooke's atom we also compare the entanglement to our previous estimates of an LDA entanglement. These were obtained using a combination of evolutionary algorithm and gradient descent, and using an LDA-based perturbative approach. We finally discuss if the position-space information entropy of the density---which can be obtained directly from the system density and hence easily from density-functional theory methods---can be considered as a proxy measure for the spatial entanglement for the test systems.Comment: 12 pages and 5 figures

Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state

Hard X-ray spectra of black hole binaries in the low/hard state are well modeled by thermal Comptonization of soft seed photons by a corona-type region with $kT$\thinspace$\sim 50${\thinspace}keV and optical depth around 1. Previous spectral studies of 1E{\thinspace}1740.7$-$2942, including both the soft and the hard X-ray bands, were always limited by gaps in the spectra or by a combination of observations with imaging and non-imaging instruments. In this study, we have used three rare nearly-simultaneous observations of 1E{\thinspace}1740.7$-$1942 by both XMM-Newton and INTEGRAL satellites to combine spectra from four different imaging instruments with no data gaps, and we successfully applied the Comptonization scenario to explain the broadband X-ray spectra of this source in the low/hard state. For two of the three observations, our analysis also shows that, models including Compton reflection can adequately fit the data, in agreement with previous reports. We show that the observations can also be modeled by a more detailed Comptonization scheme. Furthermore, we find the presence of an iron K-edge absorption feature in one occasion, which confirms what had been previously observed by Suzaku. Our broadband analysis of this limited sample shows a rich spectral variability in 1E{\thinspace}1740.7$-$2942 at the low/hard state, and we address the possible causes of these variations. More simultaneous soft/hard X-ray observations of this system and other black-hole binaries would be very helpful in constraining the Comptonization scenario and shedding more light on the physics of these systems.Comment: 6 pages, two figures, accepted for publication in A&

Entanglement distribution for a practical quantum-dot-based quantum processor architecture

We propose a quantum dot (QD) architecture for enabling universal quantum information processing. Quantum registers, consisting of arrays of vertically stacked self-assembled semiconductor QDs, are connected by chains of in-plane self-assembled dots. We propose an entanglement distributor, a device for producing and distributing maximally entangled qubits on demand, communicated through in-plane dot chains. This enables the transmission of entanglement to spatially separated register stacks, providing a resource for the realization of a sizeable quantum processor built from coupled register stacks of practical size. Our entanglement distributor could be integrated into many of the present proposals for self-assembled QD-based quantum computation (QC). Our device exploits the properties of simple, relatively short, spin-chains and does not require microcavities. Utilizing the properties of self-assembled QDs, after distribution the entanglement can be mapped into relatively long-lived spin qubits and purified, providing a flexible, distributed, off-line resource. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Robust quantum entanglement generation and generation-plus-storage protocols with spin chains

Reliable quantum communication and/or processing links between modules are a necessary building block for various quantum processing architectures. Here we consider a spin-chain system with alternating strength couplings and containing three defects, which impose three domain walls between topologically distinct regions of the chain. We show that - in addition to its useful, high-fidelity, quantum state transfer properties - an entangling protocol can be implemented in this system, with optional localization and storage of the entangled states. We demonstrate both numerically and analytically that, given a suitable initial product-state injection, the natural dynamics of the system produces a maximally entangled state at a given time. We present detailed investigations of the effects of fabrication errors, analyzing random static disorder both in the diagonal and off-diagonal terms of the system Hamiltonian. Our results show that the entangled state formation is very robust against perturbations of up to ∼10% the weaker chain coupling, and also robust against timing injection errors. We propose a further protocol, which manipulates the chain in order to localize and store each of the entangled qubits. The engineering of a system with such characteristics would thus provide a useful device for quantum information processing tasks involving the creation and storage of entangled resources

BIOMECHANIC EVALUATION OF RUNNING PERFORMANCES

Running is the final result of a very complex coordination involving a lot of different anatomo-physiological supports that are jointly provided by the neuro-muscular, the cardio-vascular, the respiratory and the metabolic systems. Given the obvious difficulties of a detailed evaluation of this specific motor-action, a method for synthetic description and analysis of the running performance has been developed. Such a method, presently tested by taking into account the sagittal plane only), is essentially based on the computation of three suitable indexes (namely P2-D, Kv, q) which integrates the information coming from both kinematic and dynamic data. The index P2-D provides a synthesis of the mean power developed by muscles at the main lower limb joints during the ground contact phase. The index Kv depends on the ratio between the previous index P2-D and the mean kinetic energy developed by the whole body during running. The third index q, pointing out an information which is similar to the well known mechanical efficiency, is depending on the ratio between the running cadence and the previously cited index K, The proposed method has been tested by taking into account various subjects who were running at different mean speed. The kinematic and dynamic data which are necessary to implement the computation of the above three indexes have been captured by using opto-electronic motion analyser (Elite system) and a piezoelectric sensed force plate. The aim of this work is to present in detail the adopted mathematical approach and to discuss, on the basis of some preliminary results, the sensitivity of the proposed method

Importance of Spin-Orbit Interaction for the Electron Spin Relaxation in Organic Semiconductors

Despite the great interest organic spintronics has recently attracted, there is only a partial understanding of the fundamental physics behind electron spin relaxation in organic semiconductors. Mechanisms based on hyperfine interaction have been demonstrated, but the role of the spin-orbit interaction remains elusive. Here, we report muon spin spectroscopy and time-resolved photoluminescence measurements on two series of molecular semiconductors in which the strength of the spin-orbit interaction has been systematically modified with a targeted chemical substitution of different atoms at a particular molecular site. We find that the spin-orbit interaction is a significant source of electron spin relaxation in these materials

Investigation of genomic DNA methylation by ultraviolet resonant Raman spectroscopy

Cytosine plays a preeminent role in DNA methylation, an epigenetic mechanism that regulates gene expression, the misregulation of which can lead to severe diseases. Several methods are nowadays employed for assessing the global DNA methylation levels, but none of them combines simplicity, high sensitivity, and low operating costs to be translated into clinical applications. Ultraviolet (UV) resonant Raman measurements at excitation wavelengths of 272 nm, 260 nm, 250 nm, and 228 nm have been carried out on isolated deoxynucleoside triphosphates (dNTPs), on a dNTP mixture as well as on genomic DNA (gDNA) samples, commercial from salmon sperm and non-commercial from B16 murine melanoma cell line. The 228 nm excitation wavelength was identified as the most suitable energy for enhancing cytosine signals over the other DNA bases. The UV Raman measurements performed at this excitation wavelength on hyper-methylated and hypo-methylated DNA from Jurkat leukemic T-cell line have revealed significant spectral differences with respect to gDNA isolated from salmon sperm and mouse melanoma B16 cells. This demonstrates how the proper choice of the excitation wavelength, combined with optimized extraction protocols, makes UV Raman spectroscopy a suitable technique for highlighting the chemical modifications undergone by cytosine nucleotides in gDNA upon hyper- and hypo-methylation events

Control of structural, electronic andoptical properties of eumelanin films by electrospraydeposition

The capability to monitor finely the physical properties of eumelanin, an important class of biopolymers, involved in melanoma cancer pathologies, whose function and intrinsic disorder still collects the interest of many investigators, was achieved by means of electrospray deposition (ESD). By alleviating the problem of the solubility of melanin through the realization of high-quality films it was possible to spread light on the unknown biopolymer supramolecular organization. In fact, on the basis of scanning probe microscopies, electron spectroscopies, and transport properties, it was possible to delineate peculiar features of the melanin organization varying from heteropolymeric to oligomeric in character and eventually turning in a cross-linked secondary molecular structure

A flexible format for exchanging pulsar data

We describe a data format currently in use amongst European institutions for exchanging and archiving pulsar data. The format is designed to be as flexible as possible with regard to present and future compatibility with different operating systems. One application of the common format is simultaneous multi-frequency observations of single pulses. A data archive containing over 2500 pulse profiles stored in this format is now available via the Internet (see http://www.mpifr-bonn.mpg.de/pulsar/data), together with a small suite of computer programs that can read, write and display the data