Nonclassicality of states and measurements by breaking classical bounds on statistics

Original article can be found at: http://pra.aps.org/ Copyright American Physical Society. DOI: 10.1103/PhysRevA.79.042105We derive exceedingly simple practical procedures revealing the quantum nature of states and measurements by the violation of classical upper bounds on the statistics of arbitrary measurements. Data analysis is minimum, and definite conclusions are obtained without evaluation of moments or any other more sophisticated procedures. These nonclassical tests are independent of other typical quantum signatures such as sub-Poissonian statistics, quadrature squeezing, or oscillatory statistics. This approach can be equally well applied to very diverse situations such as single- and two-mode fields, observables with continuous and discrete spectra, finite- and infinite-dimensional systems, and ideal and noisy measurements.Peer reviewe

The dynamical equation of the spinning electron

We obtain by invariance arguments the relativistic and non-relativistic invariant dynamical equations of a classical model of a spinning electron. We apply the formalism to a particular classical model which satisfies Dirac's equation when quantised. It is shown that the dynamics can be described in terms of the evolution of the point charge which satisfies a fourth order differential equation or, alternatively, as a system of second order differential equations by describing the evolution of both the center of mass and center of charge of the particle. As an application of the found dynamical equations, the Coulomb interaction between two spinning electrons is considered. We find from the classical viewpoint that these spinning electrons can form bound states under suitable initial conditions. Since the classical Coulomb interaction of two spinless point electrons does not allow for the existence of bound states, it is the spin structure that gives rise to new physical phenomena not described in the spinless case. Perhaps the paper may be interesting from the mathematical point of view but not from the point of view of physics.Comment: Latex2e, 14 pages, 5 figure

A new species of Anadia (Reptilia, Squamata) from the Venezuelan 'Lost World', northern South America

A new gymnophthalmid lizard of the genus Anadia Gray, 1845 is described from the summit of Abakapá-tepui, Bolívar State, Venezuela, between 2200-2242 m elevation. The new species, Anadia mcdiarmidi sp. nov., is endemic to the Chimantá Massif and seemingly also occurs on Amurí-tepui and Murei-tepui. The new taxon is mainly distinguished from all known congeners by the following combination of characters: body fairly robust, dorsal scales small and quadrangular, middorsal scales 53-57, suboculars large, subequal in size, with sometimes one scale slightly protruding downward between 4th and 5th supralabial, nasal entire, without sub-nostril groove, body uniform beige or greyish to bluish brown in life, devoid of any conspicuous pattern in males, venter immaculate golden grey in life, femoral pores 9-10 on each side in males, preanal pores absent, hemipenis globose, weakly bilobed, bordered by numerous fl ounces (>20) bearing comblike rows of minute weakly mineralized spinules. The presence of a species of Anadia, a primarily Andean genus, on the top of tepuis is of considerable interest to the understanding of the Pantepui biogeography

Topological Heat Transport and Symmetry-Protected Boson Currents

The study of non-equilibrium properties in topological systems is of practical and fundamental importance. Here, we analyze the stationary properties of a two-dimensional bosonic Hofstadter lattice coupled to two thermal baths in the quantum open-system formalism. Novel phenomena appear like chiral edge heat currents that are the out-of-equilibrium counterparts of the zero-temperature edge currents. They support a new concept of dissipative symmetry-protection, where a set of discrete symmetries protects topological heat currents, differing from the symmetry-protection devised in closed systems and zero-temperature. Remarkably, one of these currents flows opposite to the decreasing external temperature gradient. As the starting point, we consider the case of a single external reservoir already showing prominent results like thermal erasure effects and topological thermal currents. Our results are experimentally accessible with platforms like photonics systems and optical lattices.Comment: RevTeX4 file, color figure

Symmetry-protected Topological Phases at Finite Temperature

We have applied the recently developed theory of topological Uhlmann numbers to a representative model of a topological insulator in two dimensions, the Qi-Wu-Zhang model. We have found a stable symmetry-protected topological (SPT) phase under external thermal fluctuations in two-dimensions. A complete phase diagram for this model is computed as a function of temperature and coupling constants in the original Hamiltonian. It shows the appearance of large stable phases of matter with topological properties compatible with thermal fluctuations or external noise and the existence of critical lines separating abruptly trivial phases from topological phases. These novel critical temperatures represent thermal topological phase transitions. The initial part of the paper comprises a self-contained explanation of the Uhlmann geometric phase needed to understand the topological properties that it may acquire when applied to topological insulators and superconductors.Comment: Contribution to the focus issue on "Artificial Graphene". Edited by Maciej Lewenstein, Vittorio Pellegrini, Marco Polini and Mordechai (Moti) Sege