Table of contents

We consider a simple realization of an event horizon in the flow of a one-dimensional two-component Bose-Einstein condensate. Such a condensate has two types of quasiparticles; In the system we study, one corresponds to density fluctuations and the other to polarization fluctuations. We treat the case in which a horizon occurs only for one type of quasiparticles (the polarization ones). We study the one- and two-body signal associated to the analog of spontaneous Hawking radiation and demonstrate by explicit computation that it consists only in the emission of polarization waves. We discuss the experimental consequences of the present results in the domain of atomic Bose-Einstein condensates and also for the physics of exciton-polaritons in semiconductor microcavities.

A single-bit memory system is made with a Brownian particle held by an optical tweezer in a double-well potential and the work necessary to erase the memory is measured. We show that the minimum of this work is close to Landauer's bound only for a very slow erasure procedure. Instead a detailed Jarzynski equality allows us to retrieve Landauer's bound independently of the speed of this erasure procedure. For the two separated subprocesses, i.e. the transition from state 1 to state 0 and the transition from state 0 to state 0, the Jarzynski equality does not hold but the generalized version links the work done on the system to the probability that it returns to its initial state under the time-reversed procedure.

We consider periodic waves in miscible two-component Bose-Einstein condensates with repulsive nonlinear interaction constants. Exact one-phase solution is found for the case when all these constants are equal to each other (i.e., for the Manakov limit). New types of nonlinear polarization waves are considered in detail. The connection of the solutions found with experimentally observed periodic structures in two-component condensates is discussed.

Discovering the mechanism underlying the ubiquity of "$1/f^{\alpha}$" noise has been a long-standing problem. The wide range of systems in which the fluctuations show the implied long-time correlations suggests the existence of some simple and general mechanism that is independent of the details of any specific system. We argue here that a memoryless nonlinear response suffices to explain the observed nontrivial values of α: a random input noisy signal S(t) with a power spectrum varying as $1/f^{\alpha'}$, when fed to an element with such a response function R, gives an output $R(S(t))$ that can have a power spectrum $1/f^{\alpha}$ with $\alpha < \alpha'$. As an illustrative example, we show that an input Brownian noise $(\alpha'=2)$ acting on a device with a sigmoidal response function $R(S)= \text{sgn}(S)|S|^x$, with x < 1, produces an output with $\alpha = 3/2 +x$, for $0 \leq x \leq 1/2$. Our discussion is easily extended to more general types of input noise as well as more general response functions.

We investigate heat-pumped single-mode amplifiers of quantized fields in high-Q cavities based on noninverted two-level systems. Their power generation is shown to crucially depend on the capacity of the quantum state of the field to accumulate useful work. By contrast, the energy gain of the field is shown to be insensitive to its quantum state. Analogies and differences with masers are explored.

Stable vortex N-omers are constructed in coherently coupled N-component Bose-Einstein condensates. We classify all possible N-omers in terms of the mathematical graph theory and numerically construct all graphs for $N=2,3,4$. We also find that N-omers are well described as $\mathbb{C}P^{N-1}$ skyrmions when inter-component and intra-component couplings are U(N) symmetric, and we evaluate their size dependence on the Rabi coupling.

For a free particle, the coupling to its environment can be the relevant mechanism to induce quantum behavior as the temperature is lowered. We study general linear environments with a spectral density proportional to $\omega^s$ at low frequencies and consider in particular the specific heat of the free damped particle. For super-ohmic baths with $s\ge2$, a reentrant classical behavior is found. As the temperature is lowered, the specific heat decreases from the classical value of $k_{\text{B}}/2$, thereby indicating the appearence of quantum effects. However, the classical value of the specific heat is restored as the temperature approaches zero. This surprising behavior is due to the suppressed density of bath degrees of freedom at low frequencies. For s < 2, the specific heat at zero temperature increases linearly with s from $-k_{\text{B}}/2$ to $k_{\text{B}}/2$. An ohmic bath, s = 1, is thus very special in the sense that it represents the only case where the specific heat vanishes at zero temperature.

In counterfactual quantum key distribution (QKD), two remote parties can securely share random polarization-encoded bits through the blocking rather than the transmission of particles. We propose a semi-counterfactual QKD, i.e., one where the secret bit is shared, and also encoded, based on the blocking or non-blocking of a particle. The scheme is thus semi-counterfactual and not based on polarization encoding. As with other counterfactual schemes and the Goldenberg-Vaidman protocol, but unlike BB84, the encoding states are orthogonal and security arises ultimately from single-particle non-locality. Unlike any of them, however, the secret bit generated is maximally indeterminate until the joint action of Alice and Bob. We prove the general security of the protocol, and study the most general photon-number–preserving incoherent attack in detail.

In addition to self-propulsion by phoretic mechanisms that arises from an asymmetric distribution of reactive species around a catalytic motor, spherical particles with a uniform distribution of catalytic activity may also propel themselves under suitable conditions. Reactive fluctuation-induced asymmetry can give rise to transient concentration gradients which may persist under certain conditions, giving rise to a bifurcation to self-propulsion. The nature of this phenomenon is analyzed in detail, and particle-level simulations are carried out to demonstrate its existence.

Critical temperature is calculated for Bose-Einstein condensation of hard spheres with attraction using the path-integral Monte Carlo (PIMC) method and finite-size scaling. It is demonstrated that the scattering length is not the only parameter which the critical temperature depends on. It is also shown that Bose condensation may be observed in the case of negative scattering length.

The concept of off-diagonal geometric phase (GP) has been introduced in order to recover interference information about the geometry of quantal evolution where the standard GPs are not well defined. In this letter, we propose a physical setting for realizing non-Abelian off-diagonal GPs. The proposed non-Abelian off-diagonal GPs can be implemented in a cyclic chain of four qubits with controllable nearest-neighbor interactions. Our proposal seems to be within reach in various nano-engineered systems and therefore opens up for the first experimental test of the non-Abelian off-diagonal GP.

We show that the critical scaling behavior of random-field systems with short-range interactions and disorder correlations cannot be described in general by only two independent exponents, contrary to previous claims. This conclusion is based on a theoretical description of the whole $(d,N)$ domain of the d-dimensional random-field O(N) model (RFO(N)M) and points to the role of rare events that are overlooked by the proposed derivations of two-exponent scaling. Quite strikingly, however, the numerical estimates of the critical exponents of the random-field Ising model are extremely close to the predictions of the two-exponent scaling in d = 3 and d = 4, so that the issue cannot be decided only on the basis of numerical simulations in these spatial dimensions.

We analyse the constraints of an Abelian 2-form gauge theory using the Faddeev-Jackiw symplectic formalism. Further, this theory is treated as a constrained system in the context of the Batalin-Fradkin-Vilkovisky formalism to retrieve the BRST symmetry. Using the fields decompositions the effective action for the Abelian 2-form gauge theory is written in terms of a diagonalized uncanonical part and the BRST exact one. The nilpotent BRST and contracting homotopy σ closed transformations with field redefinitions are shown as the Darboux transformations used in the Faddeev-Jackiw formalism.

All-optical integrated circuits for computing and information processing have been pursued for decades as a potential strategy to overcome the speed limitations intrinsic to electronics. However, feasible on-chip integrated logic units and devices still have been limited by their size, quality, scalability, and reliability. Here we analyse all-passive on-chip optical AND and NAND logic gates made from a directional emitting cavity connecting two ultrasmall photonic-crystal heterojunction diodes. The measured transmission spectra show more than 10 dB contrast of the logic transport with a high phase tolerance, agreeing well with numerical simulations. The building of linear, passive, and ultracompact silicon optical logic gates might pave the way to construct novel nanophotonic on-chip processor architectures for future optical computing technologies.

We study the nonlinear interfacial thermal transport across atomic junctions by the quantum self-consistent mean-field (QSCMF) theory based on the nonequilibrium Green's function approach; the QSCMF theory we propose is very precise and matches well with the exact results from quantum master equation. The nonlinearity at the interface is studied by effective temperature-dependent interfacial coupling calculated from the QSCMF theory. We find that nonlinearity can provide an extra channel for phonon transport in addition to the phonon scattering which usually blocks heat transfer. For weak linearly coupled interface, the nonlinearity can enhance the interfacial thermal transport; with increasing nonlinearity or temperature, the thermal conductance shows nonmonotonical behavior. The interfacial nonlinearity also induces thermal rectification, which depends on the mismatch of the two leads and also the interfacial linear coupling.

We present results of direct numerical simulations on homoclinic gluing and ungluing bifurcations in a low-Prandtl-number ($0 \leq Pr \leq 0.025$) Rayleigh-Bénard system rotating slowly and uniformly about a vertical axis. We have performed simulations with stress-free top and bottom boundaries for several values of the Taylor number ($5 \leq Ta \leq 50$) near the instability onset. We observe a single homoclinic ungluing bifurcation, marked by the spontaneous breaking of a larger limit cycle into two limit cycles with the variation of the reduced Rayleigh number r for smaller values of $Ta\ (< 25)$. A pair of homoclinic bifurcations, instead of one bifurcation, is observed with the variation of r for slightly higher values of Ta ($25 \leq Ta \leq 50$) in the same fluid dynamical system. The variation of the bifurcation threshold with Ta is also investigated. We have also constructed a low-dimensional model which qualitatively captures the dynamics of the system near the homoclinic bifurcations for low rotation rates. The model is used to study the unfolding of bifurcations and the variation of the homoclinic bifurcation threshold with Pr.

We report an experimental study of a dilute "gas" of magnetic particles subjected to a vertical alternating magnetic field in a 3D container. Due to the torque exerted by the field on the magnetic moment of each particle, a spatially homogeneous and chaotic forcing is reached where only rotational motions are driven. This forcing differs significantly from boundary-driven systems used in most previous experimental studies on non-equilibrium dissipative granular gases. Here, no cluster formation occurs, and the equation of state displays a strong analogy with the usual gas one apart from a geometric factor. Collision statistics is also measured and shows an exponential tail for the particle velocity distribution. Most of these observations are well explained by a simple model which uncovers out-of-equilibrium systems undergoing uniform "heating".

We propose a new experimentally corroborated paradigm in which the functionality of the brain's logic-gates depends on the history of their activity, e.g. an OR-gate that turns into a XOR-gate over time. Our results are based on an experimental procedure where conditioned stimulations were enforced on circuits of neurons embedded within a large-scale network of cortical cells in vitro. The underlying biological mechanism is the unavoidable increase of neuronal response latency to ongoing stimulations, which imposes a non-uniform gradual stretching of network delays.

We report an in situ X-ray diffraction study of the high-temperature coalescence of C₆₀ and C₇₀ peapods. The monitoring of the structural evolution with time at two successive temperatures (1000 °C and 1200 °C) allows highlighting the occurrence of a two-step process for both peapods samples. The first step of the process, slower for C₇₀ peapods than for C₆₀ ones, is attributed to the transformation of individual molecules into corrugated tubules recalling the fullerenes one-dimensional periodicity. Even after long annealing time at 1000 °C this transformation is found to stagnate, until the temperature is set higher than 1050 °C, where the corrugated tubules evolve into well-formed inner nanotubes.

We study the phase-separation kinetics of a binary (AB) mixture confined in a thin film of thickness D with a temperature gradient. Starting from a Kawasaki-exchange kinetic Ising model, we use a master-equation approach to systematically derive an extension of the Cahn-Hilliard model for this system. We study the effect of temperature gradients perpendicular to the film with "neutral" (no preference for either A or B) surfaces. We highlight the rich phenomenology and pattern dynamics which arises from the interplay of phase separation and the temperature gradient.

We develop a minimal multiorbital tight-binding model with realistic hopping parameters. The model breaks the symmetry of the tetragonal point group by lowering it from C₄ to D_2d, which accurately describes the Fermi surface evolution of the electron-doped BaFe_2−xCo_xAs₂ and hole-doped Ba_1−yK_yFe₂As₂ compounds. An investigation of the phase diagram with a mean-field $t\text{-}U\text{-}V$ Bogoliubov-de Gennes Hamiltonian results in agreement with the experimentally observed electron- and hole-doped phase diagram with only one set of t, U and V parameters. Additionally, the self-consistently calculated superconducting order parameter exhibits $s^\pm$-wave pairing symmetry with a small d-wave pairing admixture in the entire doping range, which is the subtle result of the weakly broken symmetry and competing interactions in the multiorbital mean-field Hamiltonian.

We present a systematic study on the magnetoresistance (MR) behavior of bi-component antidot nanostructures consisting of the Ni₈₀Fe₂₀ antidot with holes filled with Fe dots. We observed that the stray field of the Fe dots significantly modifies the MR responses of the host Ni₈₀Fe₂₀ antidot lattice, despite the fact that Fe dots are not in a direct exchange and electric contact with the antidot lattice. The effects of temperature, applied-field orientation and antidot diameter on the MR responses are also investigated. Our experimental results are in good agreement with micromagnetic simulations.

Temperature chaos has often been reported in the literature as a rare-event–driven phenomenon. However, this fact has always been ignored in the data analysis, thus erasing the signal of the chaotic behavior (still rare in the sizes achieved) and leading to an overall picture of a weak and gradual phenomenon. On the contrary, our analysis relies on a large-deviations functional that allows to discuss the size dependences. In addition, we had at our disposal unprecedentedly large configurations equilibrated at low temperatures, thanks to the Janus computer. According to our results, when temperature chaos occurs its effects are strong and can be felt even at short distances.

In a two closely spaced nanostripes system, the coupled vortex wall undergoes a spring-like oscillatory motion (SOM) when current is applied to both nanostripes in opposite directions. The SOM may vanish, when the current density is larger than a critical value. The critical current density for destroying the SOM decreases as the interstripe spacing increases. However, as the perpendicular anisotropy of the system increases, the critical current density firstly decreases and then increases. Two competitive effects of the perpendicular anisotropy on the SOM are shown. Moreover, diagrams of without oscillation, spring behavior and motionless phases upon the current and the interstripe spacing (or the perpendicular anisotropy) are given.

Here we analyse the spectroscopic information gathered at a number of single CrO₂/Pb interfaces. We examine thin films requiring additional interfacial layers to generate long-range spin triplet proximity effect superconductivity (CrO₂/TiO₂) or not (CrO₂/Al₂O₃). We analyse the data using two theoretical models and explore the use of a parameter-free method to determine the agreement between the models and experimental observations, showing the necessary temperature range that would be required to make a definitive statement. The use of the excess current as a further tool to distinguish between models is also examined. The analysis of the spectra demonstrates that the temperature dependence of the normalised zero-bias conductance is independent of the substrate onto which the films are grown. This result has important implications for the engineering of interfaces required for the long-range spin triplet proximity effect.

Measurements of the low-temperature thermal conductivity collected on insulators with geometrical frustration produce important experimental facts shedding light on the nature of quantum spin liquid composed of spinons. We employ a model of strongly correlated quantum spin liquid located near the fermion condensation phase transition to analyze the exciting measurements of the low-temperature thermal conductivity in magnetic fields collected on the organic insulators ${\rm EtMe_3Sb[Pd(dmit)_2]_2}$ and $\kappa\text{-}{\rm (BEDT\text{-}TTF)_2Cu_2(CN)_3}$. Our analysis of the conductivity allows us to reveal a strong dependence of the effective mass of spinons on magnetic fields, to detect a scaling behavior of the conductivity, and to relate it to both the spin-lattice relaxation rate and the magnetoresistivity. Our calculations and observations are in a good agreement with experimental data.

Room temperature ferromagnetism was observed in In₂O₃ thin films doped with 5 at.% V, prepared by pulsed-laser deposition at substrate temperatures ranging from 300 to $600\ ^\circ\text{C}$. X-ray absorption fine-structure measurement indicated that V was substitutionally dissolved in the In₂O₃ host lattice, thus excluding the existence of secondary phases of V compounds. Magnetic measurements based on SQUID magnetometry and magnetic circular dichroism confirm that the magnetism is at grain boundaries and also in the grains. The overall magnetization originates from the competing effects between grains and grain boundaries.

The phase composition of the top layer of Li_1−xH_xTaO₃ waveguide layers produced at different modifications of the proton exchange (PE) technology has been analyzed based on their IR reflection spectra. These spectra contain new bands within the range $850\text{--}1050\ \text{cm}^{-1}$, each phase having its own reflection spectrum. Since the top layer is actually the strongest proton-exchanged one of all sublayers building the waveguide layer, the recognition of the top sublayer's phase in many cases could be used to make conclusions about the phases building the rest of the entire PE layer. The intrinsic stress caused by crystal lattice deformation due to the PE was calculated by an optical integral method. An attempt to explain the level of stress is made based on the phase composition of the studied samples.

We study vortex states in a 3d random-field xy model of up to one billion lattice spins at T = 0. Starting with random spin orientations, the sample freezes into the vortex-glass state with a stretched-exponential decay of spin correlations, having short correlation length and a low susceptibility, compared to vortex-free states. In a field opposite to the initial magnetization, peculiar topological objects —walls of spins still opposite to the field— emerge along the hysteresis curve. On increasing the field strength, the walls develop cracks bounded by vortex loops. The loops then grow in size and eat the walls away. Applications to magnets and superconductors are discussed.

In the search for Majorana fermions in proximity-induced topological superconducting junctions, we happened to find a signature of same-spin triplet superconductivity which appears to dominate these elusive elementary excitations. Thin-film junctions and bilayers of the doped topological insulator $\text{Bi}_2\text{Se}_3$ and the s-wave superconductor NbN exhibit conductance spectra with coexisting prominent zero-bias and coherence peaks. Various tunneling models with different pair potentials have failed to fit our data, except for the triplet $p_x+ip_y$ pair potential, which breaks time-reversal symmetry, that yielded reasonably good fits. This provides supporting evidence for proximity-induced triplet superconductivity in the $\text{Bi}_2\text{Se}_3$ layer near the interface with the NbN film.

The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap semiconductor LaZnAsO has been investigated. Our results indicate that the single phase ZrCuSiAs-type tetragonal crystal structure is preserved in (La_1−xSr_x)(Zn_1−xTM_x)AsO (TM = Mn, Fe, Co) with the doping level up to $x = 0.1$. While the system remains semiconducting, doping with Sr and Mn results in ferromagnetic order with $T_C\sim30\ \text{K}$, and doping with Sr and Fe results in a spin-glass–like state below ${\sim}6\ \text{K}$ with a saturation moment of ∼0.02 μ_B/Fe, an order of magnitude smaller than the ∼0.4 μ_B/Mn of Sr- and Mn-doped samples. The same type of magnetic state is observed neither for (Zn,Fe) substitution without carrier doping, nor for Sr- and Co-doped specimens.

A recent experimental study (Widin J. M., Schmitt A. K., Schmitt A. L., Im K. and Mahanthappa M. K., J. Am. Chem. Soc., 134 (2012) 3834) showed that polydispersity of the middle B-block has large effects on the phase behavior of ABA triblock copolymers. It is well known that the intriguing properties of ordered structures are associated with the molecular configurations and their distribution at microscale. By using a comprehensive dissipative particle dynamics (DPD) simulation method, we study the effect of middle B-block polydispersity of lamella-forming ABA triblock copolymers on the molecular configurations and the characteristics of lamellar structures. The results show that molecules with short B-blocks in a polydisperse system mainly adopt a looped configuration and preferably locate at the A/B interfaces. On the contrary, the long blocks can adopt either looped or bridged configurations with an equal probability. The bridging fraction of triblock copolymers will decrease with the increase of middle B-block polydispersity, which is due to the fact that there will be more short triblock copolymers adopting looped configurations. Such triblock copolymers with short B-blocks accumulating at the interface region can act as compatibilizers and reduce the interfacial free energy. On the other hand, the domain spacing is mainly determined by the long blocks filling in the domain center. With an increase in middle B-block polydispersity, the domain spacing will expand due to the molecular stretching of the long blocks in the domain center as well as to the reduction in interfacial free energy.

We study the effective scaling behavior of high-resolution accelerometric time series recorded at the wrists and hips of 100 subjects during sleep and wake. Using spectral analysis and detrended fluctuation analysis we find long-term correlated fluctuations with a spectral exponent $\beta \approx 1.0$ ($1/f$ noise). On short time scales, β is larger during wake ($\approx 1.4$) and smaller during sleep ($\approx 0.6$). In addition, characteristic peaks at 0.2–0.3 Hz (due to respiration) and 4–10 Hz (probably due to physiological tremor) are observed in periods of weak activity. Because of these peaks, spectral analysis is superior in characterizing effective scaling during sleep, while detrending analysis performs well during wake. Our findings can be exploited to detect sleep-wake transitions.

Both dislocation density and character in cold rolled stainless steel cause the change of acoustic nonlinearity. An analytical model considering the different oscillating motion of edge and screw dislocations is presented for the generation of ultrasonic harmonic wave during the process of multiplication and motion of dislocation. Results reveal that the edge dislocation induces stronger acoustic nonlinearity response than screw dislocation. The new model is certified by the application to the cold rolled stainless steel.

The basic building block of many carbon nanostructures like fullerenes, carbon onions or nanotubes is the truly two-dimensional material graphene. Commercial finite element codes, widely used to predict the mechanical properties of these structures, rely on the knowledge of the mechanical properties of the basic material. In this paper using an atomistic simulation approach we determine the membrane and bending stiffness of graphene, as well as the corresponding effective parameters: the effective elastic modulus $E=2.4\ \text{TPa}$, Poisson ratio $\nu =0.1844$ and thickness $h= 1.32\ \overset{\circ}{A}$. It is shown that within reasonable accuracy the obtained parameters can be applied to various loading scenarios on carbon nanostructures as long as the characteristic length of these structures is larger than $\approx 50\ \overset{\circ}{A}$. Thus, for such large and complex structures that withstand an analytical or atomistic description, commercial finite element solvers, in combination with the found effective parameters, can be used to describe these structures.

The modern world is built on the robustness of interdependent infrastructures, which can be characterized as complex networks. Recently, a framework for the analysis of interdependent networks has been developed to explain the mechanism of robustness in interdependent networks. Here, we extend this interdependent network model by considering flows in the networks, and we study the system's robustness under different attack strategies. In our model, nodes may fail because of either overload or loss of interdependency. Considering the interaction between these two failure mechanisms, it is shown that interdependent scale-free networks show extreme vulnerability. The robustness of interdependent scale-free networks is found in our simulations to be much smaller than that of the single scale-free networks or the interdependent scale-free networks without flows.

We construct a network from climate records of the atmospheric temperature at the surface level, at different geographical sites in the globe, using reanalysis data from years 1948–2010. We find that the network correlates with the North Atlantic Oscillation (NAO), both locally in the North Atlantic, and through coupling to the Southern Pacific Ocean. The existence of tele-connection links between those areas and their stability over time allows us to suggest a possible physical explanation for this phenomenon.

We use a simple Born ion continuum model to analyse the effect of solvation energy change on the translocation of a charged linear polymer molecule through a nanosized vapor gap between two fluid reservoirs. As the effective radius of the discretely spaced charges increases, our model predicts a transition from trapping to diffusion of the molecule in the vapor gap. We discuss the applicability of our model to single-stranded DNA translocations in gaps, suggest experiments to validate our prediction and propose immediate applications of this new trapping mechanism for slowing down DNA motion for electronic DNA sequencing.

We study numerically the thermoelectricity of the classical Wigner crystal placed in a periodic potential and being in contact with a thermal bath modeled by the Langevin dynamics. At low temperatures the system has sliding and pinned phases with the Aubry transition between them. We show that in the Aubry pinned phase the dimensionless Seebeck coefficient can reach very high values of several hundreds. At the same time the charge and thermal conductivity of the crystal drop significantly inside this phase. Still we find that the largest values of ZT factor are reached in the Aubry phase and for the studied parameter range we obtain $ZT \leq 4.5$. We argue that this system can provide an optimal regime for reaching high ZT factors and realistic modeling of thermoelecriticy. Possible experimental realizations of this model are discussed.

Carbon nanotube (CNT) could be exploited as a channel or source/drain region in field effect transistors (FETs). We theoretically investigate the impact of CNT doping level on a coaxially gated CNTFET's performance in the ballistic regime. The results show that the transconductance and subthreshold swing are independent of the CNT doping value. But threshold voltage and output conductance strongly depend on the channel doping level. It seems that the most important impact of CNT doping is the change in off-state current values resulting in a shift in the transfer characteristics of the device. However, it is possible to choose an optimal value of CNT doping to obtain the highest performance.