Neural wave interference in inhibition-stabilized networks

We study how excitation propagates in chains of inhibition-stabilized neural networks with nearest-neighbor coupling. The excitation generated by local stimuli in such networks propagates across space and time, forming spatiotemporal waves that affect the dynamics of excitation generated by stimuli separated spatially and temporally. These interactions form characteristic interference patterns, manifested as network preferences: for spatial and temporal frequencies of stimulus intensity, for stimulus velocities, and as contextual ("lateral") interactions between stimuli. Such preferences have been previously attributed to distinct specialized mechanisms

Rectification of Brownian particles with oscillating radii in asymmetric corrugated channels

Transport of a Brownian particle with an oscillating radius freely diffusing in an asymmetric corrugated channel was simulated over a range of driving forces for a series of temperatures and angular frequencies of radial oscillation. It was observed that there was a strong influence of self-oscillation frequency on the average particle velocity. This effect can be used to control rectification of biologically active particles as well as for their separation according to their activity, for instance in the separation of living and dead cells

Anomalous cross-field diffusion in a magnetic trap

We numerically simulated the diffusion of a charged Brownian particle confined to a plane under the action of an orthogonal magnetic field with intensity depending on the distance from a center. Despite its apparent simplicity, this system exhibits anomalous diffusion. For positive field gradients, radial and angular dynamics are asymptotically subdiffusive, with exponents given by simple analytical expressions. In contrast, when driven by a weakly decaying field, the particle attains normal diffusion only after exceedingly long superdiffusive transients. These mechanisms can be related to Bohm diffusion in magnetized plasmas

Renninger’s Gedankenexperiment, the collapse of the wave function in a rigid quantum metamaterial and the reality of the quantum state vector

A popular interpretation of the “collapse” of the wave function is as being the result of a local interaction (“measurement”) of the quantum system with a macroscopic system (“detector”), with the ensuing loss of phase coherence between macroscopically distinct components of its quantum state vector. Nevetheless as early as in 1953 Renninger suggested a Gedankenexperiment, in which the collapse is triggered by non-observation of one of two mutually exclusive outcomes of the measurement, i.e., in the absence of interaction of the quantum system with the detector. This provided a powerful argument in favour of “physical reality” of (nonlocal) quantum state vector. In this paper we consider a possible version of Renninger’s experiment using the light propagation through a birefringent quantum metamaterial. Its realization would provide a clear visualization of a wave function collapse produced by a “non-measurement”, and make the concept of a physically real quantum state vector more acceptable

Narrating and mapping Russia: From Terra Incognita to a charted space on the road to Cathay

In the 16th century most of Russia is still a terra incognita with a highly dubious and mostly mythologized geography, anthropology, and sociology. In this article we look at some texts of the Early Modern period – Sir Thomas Smithes Voiage and Entertainment in Rushia (1605), Peter Mundy’s Travel Writings of 1640–1641, and The Voiages and Travels of John Struys (1676–1683) – and try to uncover the transformation of the obscure country into a more or less charted space, filled with narratives of adventures and travels in an enigmatic land on the verge of Europe, where exotic cultures are drawn together in a flamboyant mix. It is travel narrative that actually charts the territory and provides an explanation from which stems a partial understanding, physical and cultural, of the “Land of the Unpredictable.

Dirac-Weyl points’ manipulation using linear polarised laser field in Floquet crystals for various graphene superlattices

We investigate the changes in the energy spectrum of the graphene monolayer subjected to linear polarised laser beam and external periodically modulated static field (electric and magnetic). Floquet theory and the resonance approximation are used to analyse the energy spectrum and, in particular, the creation and the destruction of the Dirac-Weyl points. We found that at certain conditions the graphene is transformed into the two-dimensional Weyl metals, where each of the two original graphene Dirac cones is split into pairs of the Weyl cones. We also show that altering the laser's beam incidence(tilting) angle may lead to appearing and disappearing of the pairs of Weyl points, the opening gap in the spectrum, and its efficient manipulation

Current induced decomposition of Abrikosov vortices in p-n layered superconductors and heterostructures

We describe the decomposition of Abrikosov vortices into decoupled pancake vortices in superconductors having both electron and hole charge carriers. We estimate the critical current of such a decomposition, at which a superconducting-normal state transition occurs, and find that it is very sensitive to the magnetic field and temperature. The effect can be observed in recently synthesized self-doped high-Tc layered superconductors with electrons and holes coexisting in different Cu-O planes and in artificial p-n superconductor heterostructures. The sensitivity of the critical current to a magnetic field may be used for sensors and detectors of a magnetic field, which can be built up from the superconductor heterostructures

Manipulating the anisotropy of the Dirac-Cone in graphene by laser fields

One of the most striking properties of graphene is the relativistic-like Dirac-Cone spectrum of charge carriers. By applying high-frequency laser fields, the system can be described with the use of similar spectrum which is based on a concept of electron quasi-energy. There in this spectrum a creation and annihilation of new Dirac points and cones as well as opening a gap may arise. This allows controlling electron motion without applying DC periodic fields which are effectively described by graphene superlattices. Here we demonstrate that coherent electromagnetic fields applied to graphene can generate new Dirac and Weyl points, induce Lifshitz quantum phase transition for slightly doped graphene and produce an anisotropy of the Dirac cones, which can be even infinite

Harmonic mixing in two coupled qubits: Quantum synchronization via ac drives

Simulating a system of two driven coupled qubits, we show that the time-averaged probability to find one driven qubit in its ground or excited state can be controlled by an ac drive in the second qubit. Moreover, off-diagonal elements of the density matrix responsible for quantum coherence can also be controlled via driving the second qubit; that is, quantum coherence can be enhanced by appropriate choice of the biharmonic signal. Such a dynamic synchronization of two differently driven qubits has an analogy with harmonic mixing of Brownian particles forced by two signals through a substrate. Nevertheless, the quantum synchronization in two qubits occurs due to multiplicative coupling of signals in the qubits rather than via a nonlinear harmonic mixing for a classical nanoparticle. Quantum harmonic mixing proposed here can be used to manipulate one driven qubit by applying an additional ac signal to the other qubit coupled with the one we have to control

Quasi-superradiant soliton state of matter in quantum metamaterials

Strong interaction of a system of quantum emitters (e.g., two-level atoms) with electromagnetic field induces specific correlations in the system accompanied by a drastic insrease of emitted radiation (superradiation or superfluorescence). Despite the fact that since its prediction this phenomenon was subject to a vigorous experimental and theoretical research, there remain open question, in particular, concerning the possibility of a first order phase transition to the superradiant state from the vacuum state. In systems of natural and charge-based artificial atome this transition is prohibited by "no-go" theorems. Here we demonstrate numerically a similar transition in a one-dimensional quantum metamaterial - a chain of artificial atoms (qubits) strongly interacting with classical electromagnetic fields in a transmission line. The system switches from vacuum state with zero classical electromagnetic fields and all qubits being in the ground state to the quasi-superradiant (QS) phase with one or several magnetic solitons and finite average occupation of qubit excited states along the transmission line. A quantum metamaterial in the QS phase circumvents the "no-go" restrictions by considerably decreasing its total energy relative to the vacuum state by exciting nonlinear electromagnetic solitons with many nonlinearly coupled electromagnetic modes in the presence of external magnetic field