Noise resilience and entanglement evolution in two nonequivalent classes of quantum algorithms

The speedup provided by quantum algorithms with respect to their classical counterparts is at the origin of scientific interest in quantum computation. However, the fundamental reasons for such a speedup are not yet completely understood and deserve further attention. In this context, the classical simulation of quantum algorithms is a useful tool that can help us in gaining insight. Starting from the study of general conditions for classical simulation, we highlight several important differences between two nonequivalent classes of quantum algorithms. We investigate their performance under realistic conditions by quantitatively studying their resilience with respect to static noise. This latter refers to errors affecting the initial preparation of the register used to run an algorithm. We also compare the evolution of the entanglement involved in the different computational processes.

Sildenafil (Viagra)-induced spontaneous intracerebral haemorrhage

Sildenafil (Viagra) has been developed as a drug to help male impotence. It has a direct effect on the vasculature of the corpus cavernosum. A case of spontaneous intracerebral haemorrhage (ICH) following the illicit use of Viagra is reported. A discussion of drug-induced ICH is included.

Low SNR Capacity for MIMO Rician and Rayleigh-Product Fading Channels with Single Co-channel Interferer and Noise

This paper studies the ergodic capacity of multiple-input multiple-output (MIMO) systems with a single co-channel interferer in the low signal-to-noise-ratio (SNR) regime. Two MIMO models namely Rician and Rayleigh-product channels are investigated. Exact analytical expressions for the minimum energy per information bit, Eb/N0min, and wideband slope, S0, are derived for both channels. Our results show that the minimum energy per information bit is the same for both channels while their wideband slopes differ significantly. Further, the impact of the numbers of transmit and receive antennas, the Rician K factor, the channel mean matrix and the interference-to-noise-ratio (INR) on the capacity, is addressed. Results indicate that interference degrades the capacity by increasing the required minimum energy per information bit and reducing the wideband slope. Simulation results validate our analytical results.

"The pride of noise": drums and their repercussions in early modern England

This article draws on a wide range of literary and archival sources in order to explore the cultural resonances of drumming in England during the 16th and 17th centuries. It concentrates not on instrument design and playing techniques but on the varied meanings that contemporaries attached to the ubiquitous sound of the drum. The discussion begins and ends with the unmistakable military associations of drumming. In between, consideration is also given to a range of interconnected but sometimes contradictory resonances that appear to have endowed drums with considerable cultural significance. Drums spoke, for example, of authority and they worked hard to impose order in urban streets. They also played their part in the contemporary culture of punishment, and many miscreants were subjected to the humiliation of public percussion. Beyond this, drums were particularly potent in their ability to express masculinity, and female drummers were rare and remarkable. The primal potency of the instrument also rendered it valuable to the insubordinate, and rioters—like soldiers— were regularly called together 'by the drum'. Lastly, the sound of the drum was sometimes intensely festive and could also be used to publicize special events such as dramatic performances and the display of curiosities. The repercussions of drumming were thus varied, and confusion sometimes resulted when the different possibilities became entangled.

Spontaneous spin polarization and charge localization in metal nanowires: the role of a geometric constriction

An idealized jellium model of conducting nanowires with a geometric constriction is investigated by density functional theory (DFT) in the local spin density (LSD) approximation. The results reveal a fascinating variety of spin and charge patterns arising in wires of sufficiently low (r(s) >= 15) average electron density, pinned at the indentation by an apparent attractive interaction with the constriction. The spin-resolved frequency-dependent conductivity shows a marked asymmetry in the two spin channels, reflecting the spontaneous spin polarization around the wire neck. The relevance of the computational results is discussed in relation to the so-called 0.7 anomaly found by experiments in the low-frequency conductivity of nanowires at near-breaking conditions (see 2008 J. Phys.: Condens Matter 20, special issue on the 0.7 anomaly). Although our mean-field approach cannot account for the intrinsic many-body effects underlying the 0.7 anomaly, it still provides a diagnostic tool to predict impending transitions in the electronic structure.

Spontaneous spin polarization in geometrically constricted metal nanowires

The electronic structure of thin conducting wires with a narrow geometric constriction has been determined by density-functional theory computations in the local spin density approximation. Spontaneous spin polarization arises in nominally paramagnetic wires at sufficiently low density (r(s)>= 15). Real-space spin-polarization maps show a fascinating variety of magnetic structures pinned at the constriction. The frequency-dependent conductivity is different for the spin-up and spin-down channels and significantly lower than in wires of identically vanishing spin polarization.