The Road to Quantum Computational Supremacy

We present an idiosyncratic view of the race for quantum computational supremacy. Google's approach and IBM challenge are examined. An unexpected side-effect of the race is the significant progress in designing fast classical algorithms. Quantum supremacy, if achieved, won't make classical computing obsolete.Comment: 15 pages, 1 figur

Scalar <i>φ</i>⁴ field theory for active-particle phase separation

Recent theories predict phase separation among orientationally disordered active particles whose propulsion speed decreases rapidly enough with density. Coarse-grained models of this process show time-reversal symmetry (detailed balance) to be restored for uniform states, but broken by gradient terms; hence detailed-balance violation is strongly coupled to interfacial phenomena. To explore the subtle generic physics resulting from such coupling we here introduce `Active Model B'. This is a scalar $\phi^4$ field theory (or phase-field model) that minimally violates detailed balance via a leading-order square-gradient term. We find that this additional term has modest effects on coarsening dynamics, but alters the static phase diagram by creating a jump in (thermodynamic) pressure across flat interfaces. Both results are surprising, since interfacial phenomena are always strongly implicated in coarsening dynamics but are, in detailed-balance systems, irrelevant for phase equilibria.Comment: 15 pages, 7 figure

Intentional communication between wild bonnet macaques and humans

Comparative studies of nonhuman communication systems could provide insights into the origins and evolution of a distinct dimension of human language: intentionality. Recent studies have provided evidence for intentional communication in diferent species but generally in captive settings. We report here a novel behaviour of food requesting from humans displayed by wild bonnet macaques Macaca radiata, an Old World cercopithecine primate, in the Bandipur National Park of southern India. Using both natural observations and feld experiments, we examined four diferent behavioural components— coo-calls, hand-extension gesture, orientation, and monitoring behaviour—of food requesting for their conformity with the established criteria of intentional communication. Our results suggest that food requesting by bonnet macaques is potentially an intentionally produced behavioural strategy as all the food requesting behaviours except coo-calls qualify the criteria for intentionality. We comment on plausible hypotheses for the origin and spread of this novel behavioural strategy in the study macaque population and speculate that the cognitive precursors for language production may be manifest in the usage of combination of signals of diferent modalities in communication, which could have emerged in simians earlier than in the anthropoid ape

Thermal concurrence mixing in a one-dimensional Ising model

The natural thermal entanglement in an Ising ring in an external magnetic field was studied. The interactions of two qubits via the Ising interaction in a magnetic field orthogonal to the z direction was analyzed. A theorem for the concurrence mixing due to occupation of the ground and the excited state was formulated. The variation of entanglement with the orientation of magnetic field was numerically considered

Targeting nominal income growth or inflation?

SIGLEAvailable from British Library Document Supply Centre-DSC:3597.9512(2341) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Crucial role of Black Sea warming in amplifying the 2012 Krymsk precipitation extreme

Over the past 60 years, both average daily precipitation intensity and extreme precipitation have increased in many regions1, 2, 3. Part of these changes, or even individual events4, 5, have been attributed to anthropogenic warming6, 7. Over the Black Sea and Mediterranean region, the potential for extreme summertime convective precipitation has grown8 alongside substantial sea surface temperature increase. A particularly devastating convective event experienced in that region was the July 2012 precipitation extreme near the Black Sea town of Krymsk9. Here we study the effect of sea surface temperature (SST) increase on convective extremes within the region, taking the Krymsk event as a showcase example. We carry out ensemble sensitivity simulations with a convection-permitting atmospheric model and show the crucial role of SST increase in the extremeness of the event. The enhancement of lower tropospheric instability due to the current warmer Black Sea allows deep convection to be triggered, increasing simulated precipitation by more than 300% relative to simulations with SSTs characteristic of the early 1980s. A highly nonlinear precipitation response to incremental SST increase suggests that the Black Sea has exceeded a regional threshold for the intensification of convective extremes. The physical mechanism we identify indicates that Black Sea and Mediterranean coastal regions may face abrupt amplifications of convective precipitation under continued SST increase, and illustrates the limitations of thermodynamical bounds for estimating the temperature scaling of convective extremes