Macroscopic Regime Research Articles

Large Quantum Delocalization of a Levitated Nanoparticle Using Optimal Control: Applications for Force Sensing and Entangling via Weak Forces.

We propose to optimally control the harmonic potential of a levitated nanoparticle to quantum delocalize its center-of-mass motional state to a length scale orders of magnitude larger than the quantum zero-point motion. Using a bang-bang control of the harmonic potential, including the possibility of inverting it, the initial ground-state-cooled levitated nanoparticle coherently expands to large scales and then contracts to the initial state in a time-optimal way. We show that this fast loop protocol can be used to enhance force sensing as well as to dramatically boost the entangling rate of two weakly interacting nanoparticles. We parameterize the performance of the protocol, and therefore the macroscopic quantum regime that could be explored, as a function of displacement and frequency noise in the nanoparticle's center-of-mass motion. This noise analysis accounts for the sources of decoherence relevant to current experiments.

Violating the Leggett-Garg inequalities with classical light

In an endeavour to better define the distinction between classical macroscopic and quantum microscopic regimes, the Leggett-Garg inequalities were established as a test of macroscopic-realistic theories, which are commonly thought to be a suitable class of descriptions for classical dynamics. The relationship between their violation and non-classicality is however not obvious. We show that classical states of light, which in the quantum optical sense are any convex sums of coherent states, may not satisfy the Leggett-Garg inequalities. After introducing a simple Mach-Zehnder setup and showing how to obtain a violation with a single photon using negative measurements, we focus on classical states of light, in particular those of low average photon number. We demonstrate how one can still perform negative measurements with an appropriate assignment of variables, and show that the inequalities are violable with coherent states. Finally, we abandon initial phase reference and demonstrate that the violation is still possible, in particular with thermal states of light, and we investigate the effect of intermediate dephasing.

Frustration effect on escape rate in Josephson junctions between single-band and three-band superconductors in the macroscopic quantum tunneling regime

The escape rate of S → R switching (from superconducting S state to resistive R state) in Josephson junction formed by s-wave single-band (SB) and three-band (ThB) superconductors (SB/ThB junctions) in macroscopic quantum tunneling regime is investigated. We use the effective critical current approximation in SB/ThB junctions. It was shown that escape rate can exhibit qualitative features in the case of frustration effects in ThB superconductors. Inclusion of Leggett modes in ThB superconductors leads to enhancement of escape rate in three-channel Josephson junction in comparison with single-channel junctions.

Multi-scale three-domain approach for coupling free flow and flow in porous media including droplet-related interface processes

Drops on a free-flow/porous-medium-flow interface have a strong influence on the exchange of mass, momentum and energy between the two macroscopic flow regimes. Modeling droplet-related pore-scale processes in a macro-scale context is challenging due to the scale gap, but might be rewarding due to relatively low computational costs. We develop a three-domain approach to model drop formation, growth, detachment and film flow in a lower-dimensional interface domain. A simple upscaling technique allows to compute the drop-covered interface area fraction which affects the coupling fluxes. In a first scenario, only drop formation, growth and detachment are taken into account. Then, spreading and merging due to lateral fluxes are considered as well. The simulation results show that the impact of these droplet-related processes can be captured. However, extensions are necessary to represent the influence on the free flow more precisely.

Early-photon reflectance fluorescence molecular tomography for small animal imaging: Mathematical model and numerical experiment.

The paper presents an original approach to time-domain reflectance fluorescence molecular tomography (FMT) of small animals. It is based on the use of early arriving photons and state-of-the-art compressed-sensing-like reconstruction algorithms and aims to improve the spatial resolution of fluorescent images. We deduce the fundamental equation that models the imaging operator and derive analytical representations for the sensitivity functions which are responsible for the reconstruction of the fluorophore absorption coefficient. The idea of fluorescence lifetime tomography with our approach is also discussed. We conduct a numerical experiment on 3D reconstruction of box phantoms with spherical fluorescent inclusions of small diameters. For modeling measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry. It provides for large source-receiver separations which correspond to the macroscopic regime. Two compressed-sensing-like reconstruction algorithms are used to solve the inverse problem. These are the algebraic reconstruction technique with total variation regularization and our modification of the fast iterative shrinkage-thresholding algorithm. Results of our numerical experiment show that our approach is capable of achieving as good spatial resolution as 0.2 mm and even better at depths to 9 mm inclusive.

Regimes of flow through cylinder arrays subject to steady pressure gradients

Flows through periodic cylinder arrays have been studied extensively for applications to heat exchangers, porous media, chemical reactors, and computational fluid mechanics. Nevertheless, the variation of the pore and macro-scale flow-regimes with porosity, driving pressure gradient, and cylinder arrangement remains not fully explored. We consequently perform a thorough parametric study of such regimes for both inline and staggered arrays of circular cylinders. The Navier–Stokes and continuity equations are solved using finite-volume and immersed boundary methods. We vary the porosity from minimum values for which cylinders nearly touch, to values approaching unity. We vary the Reynolds number from values producing Stokes flow to those producing pore-scale vortex shedding. Using the results of over 1000 simulations, we explore how competition between viscous and inertial effects produces five macroscopic flow regimes. We document the validity limits of each regime, and explore how they impact the modelling of non-Darcy flow regimes. We find the practice of fitting Forchheimer-type equations to data from a wide range of Reynolds numbers produces conflicting results in the literature. For inline arrays, the Forchheimer regime is not always present, and has a smaller validity regime than alternative models. For staggered arrays, the Forchheimer regime has a strong presence, but care must be taken to account for the presence of two different Forchheimer-type regimes. We also show that transition to vortex shedding is sensitive to the numerical domain size, because the mode of instability need not be periodic over the same unit cell as the steady flow. This significantly complicates the study of vortex shedding.

An inspired nanoscale system to evaluate interfacial behavior of layered structures

Accurately evaluating interfacial behavior is key and of exceptional meaning to characterize the mechanical behavior of layered structures. Different from various sensors in macroscopic regime, it is still a challenge to realize monitoring of interfacial behavior at nanoscale. Inspired by the prayer wheel, i.e., a Buddhist ritual apparatus, a novel nanoscale system based on double-walled carbon nanotubes is proposed and its rotating dynamics performance is investigated by molecular dynamics simulation. A theoretical model is also established to explain the underlying mechanism. It is found that the proposed nanoscale system functions well to predict the crack propagation speed of a layered structure. What is more, the dynamics response affected by various interfacial and dimension parameters is evaluated. The results not only provide insights into the design the small-scale interfacial sensors of layered nanostructures, but also would be promising for health monitoring of laminate structures.

Two scenarios for the onset and suppression of collective oscillations in heterogeneous populations of active rotators.

We consider the macroscopic regimes and the scenarios for the onset and the suppression of collective oscillations in a heterogeneous population of active rotators composed of excitable or oscillatory elements. We analyze the system in the continuum limit within the framework of Ott-Antonsen reduction method, determining the states with a constant mean field and their stability boundaries in terms of the characteristics of the rotators' frequency distribution. The system is established to display three macroscopic regimes, namely the homogeneous stationary state, where all the units lie at the resting state, the global oscillatory state, characterized by the partially synchronized local oscillations, and the heterogeneous stationary state, which includes a mixture of resting and asynchronously oscillating units. The transitions between the characteristic domains are found to involve a complex bifurcation structure, organized around three codimension-two bifurcation points: a Bogdanov-Takens point, a cusp point, and a fold-homoclinic point. Apart from the monostable domains, our study also reveals two domains admitting bistable behavior, manifested as coexistence between the two stationary solutions or between a stationary and a periodic solution. It is shown that the collective mode may emerge via two generic scenarios, guided by a saddle-node of infinite period or the Hopf bifurcation, such that the transition from the homogeneous to the heterogeneous stationary state under increasing diversity may follow the classical paradigm, but may also be hysteretic. We demonstrate that the basic bifurcation structure holds qualitatively in the presence of small noise or small coupling delay, with the boundaries of the characteristic domains shifted compared to the noiseless and the delay-free case.

Toward high contrast and high-resolution microscopic ghost imaging.

In this study, the influence of speckle size on contrast-to-noise ratio (CNR) and resolution is examined based on the object dimensions in the macroscopic and microscopic regimes. This research shows that for microscopic samples the conventional scaling laws are no longer effective and the CNR does not counter-propagate in the same manner as the resolution. To our knowledge, a deviation in CNR scaling on speckle size is observed for the first time in the field of microscopic ghost imaging. This result was verified using two different sample shapes. In addition, numerical analysis revealed that the noise of the photodiode is a limiting factor for the CNR. Based on these findings, the conditions for identifying the parameter set that maximizes the CNR and provides high resolution images was defined, which achieving high-quality microscopic ghost images.

Influence of unconventional current-phase relation of Josephson junction on the escape rate in macroscopic quantum tunneling regime

In this study, we carried out the analysis of the quantum fluctuations on Josephson junction (JJ) dynamics with unconventional current-phase relation (CPR). We analyzed two case CPR: anharmonic term case and the case of Majorana term. The expression was obtained for the escape rate in macroscopic tunneling regime. It is shown that the changing of the escape rate JJ with unconventional CPR is determined by the renormalized critical current of JJ.

Tunable nanomechanical performance regimes in ceramic nanowires

At the macroscopic size regime, ceramic materials exhibit brittle fracture and catastrophic failure when they are subjected to mechanical loads that exceed their characteristic strength. In this report, we present recoverable plasticity in alpha-phase, potassium stabilized manganese dioxide nanowire (α-K0.13MnO2 NW) crystals when they are subjected to atomic force microscopy (AFM) based three-point bending tests at very low loading rates. The force-deflection curves and AFM scans obtained from these measurements reveal yielding and extended plasticity in the NWs during the loading process, while the large plastic deformation is recovered spontaneously during the unloading process. However, the same material system exhibits failure via fracture at substantially higher strengths when it is subjected to bending tests at nearly an order of magnitude higher loading rates. These results highlight an important new pathway to controllably tune the nanomechanical performance of these technologically important nanoceramics for application-specific needs: either achieve self-reversible and ultra-large plasticity, or achieve substantially higher fracture strengths that approach the intrinsic limits of the material system.

Soft Robotics Programmed with Double Crosslinking DNA Hydrogels

AbstractDNA nanotechnology is developed for decades to construct dynamic responsive systems in optics, quantum electronics, and therapeutics. While DNA nanotechnology is a powerful tool in nanomaterials, it is rare to see successful applications of DNA molecules in the macroscopic regime of material sciences. Here, a novel strategy to magnify the nanometer scale DNA self‐assembly into a macroscopic mechanical responsiveness is demonstrated. By incorporating molecularly engineered DNA sequences into a polymeric network, a new type of responsive hydrogel (D‐gel), whose overall morphology is dynamically controlled by DNA hybridization‐induced double crosslinking is able to be created. As a step toward manufacturing, the D‐gel in combination with a bottom‐up 3D printing technology is employed to rapidly create modular macroscopic structures that feature programmable reconfiguration and directional movement, which can even mimic the complex gestures of human hands. Mechanical operations such as catch and release are demonstrated by a proof‐of‐concept hydrogel palm, which possessed great promise for future engineering applications. Compared with previously developed DNA hydrogels, the D‐gel features an ease of synthesis, faster response, and a high degree of programmable control. Moreover, it is possible to scale up the production of D‐gel containing responsive devices through direct 3D printing.

Active energy transport and the role of symmetry breaking in microscopic power grids

We study the transfer of energy through a network of coupled oscillators, which represents a minimalmicroscopic power grid connecting multiple active quantum machines. We evaluate the resulting energy currentsin the macroscopic, thermal, and quantum regime and describe how transport is affected by the competitionbetween coherent and incoherent processes and nonlinear saturation effects. Specifically, we show that thetransfer of energy through such networks is strongly influenced by a nonequilibrium phase transition between anoise-dominated and a coherent transport regime. This transition is associated with the formation and breakingof spatial symmetries and is identified as a generic feature of active networks. Therefore, these findings haveimportant practical consequences for the distribution of energy over coherent microwave, optical, or phononicchannels, in particular close to or at the quantum limit

Effect of Asymmetric Anchoring Groups on Electronic Transport in Hybrid Metal/Molecule/Graphene Single Molecule Junctions.

A combined experimental and theoretical study on molecular junctions with asymmetry in both the electrode type and in the anchoring group type is presented. A scanning tunnelling microscope is used to create the "asymmetric" Au-S-(CH2 )n-COOH-graphene molecular junctions and determine their conductance. The measurements are combined with electron transport calculations based on density functional theory (DFT) to analyze the electrical conductance and its length attenuation factor from a series of junctions of different molecular length (n). These results show an unexpected trend with a rather high conductance and a smaller attenuation factor for the Au-S-(CH2 )n -COOH-graphene configuration compared to the equivalent junction with the "symmetrical" COOH contacting using the HOOC-(CH2 )n -COOH series. Owing to the effect of the graphene electrode, the attenuation factor is also smaller than the one obtained for Au/Au electrodes. These results are interpreted through the relative molecule/electrode couplings and molecular level alignments as determined with DFT calculations. In an asymmetric junction, the electrical current flows through the less resistive conductance channel, similarly to what is observed in the macroscopic regime.

Continuum Mechanics as a Computable Coarse-Grained Picture of Molecular Dynamics

In this paper, I determine the minimum amount of information that continuum mechanics needs to obtain from Newtonian molecular dynamics, in order to avail itself of stress-strain responses uniformly valid for a vast range of macroscopic regimes, being quantitatively determined by microscopic physical properties. Described from the opposite, bottom-up point of view, the procedure I put forward uses the basic kinematic and dynamical machinery of continuum mechanics to upscale molecular dynamics to the macroscopic level in a practicable and efficient way.

Josephson-like dynamics of the superconducting LaAlO3/SrTiO3 interface

In this article, we show that the two-dimensional electron gas formed at the ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ interface behaves as a Josephson junction array. In particular, it exhibits a stochastic switching of the superconducting critical current, which qualitatively follows the dynamics of the resistively and capacitively shunted Josephson junction model. The switching current distribution (SCD) has been measured as a function of temperature and back-gate voltage. At low temperatures a clear saturation of the standard deviation of the SCD is observed, possibly indicating the presence of a macroscopic quantum tunneling regime with phase diffusion. Through the gate voltage we modify the damping of the array and compare it to artificial arrays of junctions.

Observation of type‐II kind of correlated photon generation from a classical circularly polarized slot antenna

AbstractIn this communication, an important observation on the generation of the Type II kind of correlated photons at the macroscopic regime is presented. In the optical regime, the entangled photon generation is well established. But, in the microwave (macroscopic) regime there is no any radiator which can radiate two photons of entangled spin states is reported. Accidentally, it is observed that a fundamental circularly polarized slot antenna could radiate photons with correlated spin states in the opposite spatial directions. It is simulated and experimentally observed. The dimensions of the same design could be scaled up or down to use this principle to be implemented at the other frequencies of the electromagnetic spectrum like millimeter waves, Tera Hertz waves, etc. also.

Numerical Simulation of Ore Particle Flow Behaviour through a Single Drawpoint under the Influence of a Flexible Barrier

A model of the mass draw and synchronous filling no-top-pillar shrinkage stoping method was created based on the particle element theory and PFC2D software. A numerical simulation of the ore particle flow behaviour through a single drawpoint under the influence of a flexible barrier was performed; following which, a visualization of the change process in the marked layers, draw column, flexible barrier, and cavity was obtained. Finally, the results demonstrated the following. (1) Before the ore particles at the highest horizon were drawn, the morphology of the draw column had an ellipsoidal (whole, closed, and approximate) shape, but after the ore particles were drawn, the morphology of the draw column had a gyroscopic shape (i.e., the shape of a spinning top). (2) The height of the draw column increased rapidly and exponentially in the early period of the draw, presented a linear growth tendency during the medium period with an increase in the accumulated mass drawn, and remained at a certain value in the later period. (3) The morphology of the flexible barrier presented a Gaussian distribution on the whole, but its bottom had an analogous parabola morphology, particularly in the late stage. (4) The cavity began to form with the ore particles at the highest horizon drawn; the cavity development presented an evolutionary process from the microscopic to macroscopic regime, and the morphology of the cavity was crescent in the early stage and triangular in the late stage.

Uncovering the magnetic properties of the AgxNiy (x+y=55) nanoalloys in the whole composition range

Nickel and silver are metals with interesting properties of technological relevance: nickel is a well known ferromagnet and silver has antibacterial properties. Both exist in the face centered cubic phase but are immiscible. In the context of alloys at the nanoscale, one can play with the size to fine tune a desired property, or to achieve new properties and functionalities that do not exist at the macroscopic regime. In this work, we explore how the subtle interaction between Ni and Ag triggers the chemical order, the electronic structure, and the magnetic properties of a AgNi nanoalloy of 55 atoms, a size that can accommodate core/shell configurations with sizable parts. Calculations are conducted within the density functional theory at the generalized gradient approximation for exchange and correlation. We determine, in the whole composition range, the chemical order, absolute and relative stabilities by means of binding energy, excess energy and second energy difference, as well as total and part-projected spin-polarized electronic densities of states and local charge and spin magnetic moments distribution. Ni-core/Ag-shell structures are particularly stable, but contrary to what one would expect by simply extrapolating the properties of the pure Ag and Ni clusters or of pure fcc bulks, we find unexpected behaviors along the composition range, such as quenched magnetic moments in Ni, total magnetic moments essentially contributed in some cases by Ag, or electronic charge transfer that changes its sign depending on the stoichiometry. These behaviors lead to magnetic transitions as a function of the composition, and differ, in some cases, from those of the smaller 13-atoms AgNi nanoalloys of the same symmetry with which we compare, a further demonstration of the complex nature of nanostructures. The above trends are robust against ionization and electron capture.

Macroscopic quantum escape of Bose-Einstein condensates: Analysis of experimentally realizable quasi-one-dimensional traps

The variational JWKB method is used to determine experimentally accessible macroscopic quantum tunneling regimes of quasibound Bose-Einstein condensates in two quasi-one-dimensional trap configurations. The potentials can be created by magnetic and optical traps: a symmetric trap from two offset Gaussian barriers and a tilt trap from a linear gradient and Gaussian barrier. Scaling laws in barrier parameters, ranging from inverse polynomial to square root times exponential, are calculated and used to elucidate different dynamical regimes, such as when classical oscillations dominate tunneling rates in the symmetric trap. The symmetric trap is found to be versatile, with tunneling times at and below 1 s, able to hold ${10}^{3}--{10}^{4}$ atoms, and realizable for atoms ranging from rubidium to lithium, with unadjusted scattering lengths. The tilt trap produces subsecond tunneling times, is able to hold a few hundred atoms of lighter elements such as lithium, and requires the use of Feshbach resonance to reduce scattering lengths. To explore a large parameter space, an extended Gaussian variational ansatz is used, which can approximate large traps with Thomas-Fermi profiles. Nonlinear interactions in the Gross-Pitaevskii equation are shown to produce additional effective mean-field barriers, affecting scaling laws.