Preservation Of Coherence Research Articles

Room-temperature valley coherence in a polaritonic system

The emerging field of valleytronics aims to coherently manipulate an electron and/or hole’s valley pseudospin as an information bearing degree of freedom (DOF). Monolayer transition metal dichalcogenides, due to their strongly bound excitons, their degenerate valleys and their seamless interfacing with photons are a promising candidate for room temperature valleytronics. Although the exciton binding energy suggests room temperature valley coherence should be possible, it has been elusive to-date. A potential solution involves the formation of half-light, half-matter cavity polaritons based on 2D material excitons. It has recently been discovered that cavity polaritons can inherit the valley DOF. Here, we demonstrate the room temperature valley coherence of valley-polaritons by embedding a monolayer of tungsten diselenide in a monolithic dielectric cavity. The extra decay path introduced by the exciton-cavity coupling, which is free from decoherence, is the key to room temperature valley coherence preservation. These observations paves the way for practical valleytronic devices.

Coherence and entropy squeezing in the spin-boson model under non-Markovian environment

We study the dynamical behavior of the coherence and squeezing for a two-level system immersed in an environment modeled by a spin degree of freedom in a magnetic field coupled linearly to an oscillator bath with non-Markovian environment. The dependence of the coherence and squeezing on the system and reservoir parameters shows that these quantities could be greatly controlled and manipulated with the assistance of the reservoir cutoff frequency, system oscillator frequency, and reservoir temperature. Moreover, we show that the proper choice of the external control field can make further control on the coherence and squeezing of the atomic system under the effect of environmental noises. The results show new interest features that are usefully utilized in controlling the physical quantities and show how the enhancement and preservation of coherence and squeezing can greatly benefit from the combination of the all physical parameters.

Analogue-based colorization of remote sensing images using textural information

Satellite images are richer than ever before. For example, new Landsat-8 images with their 11 bands carry much more information than older generations of satellites. These differences in spectral representation imply a major difficulty for assessing long-term land surface changes. The easiest solution is to reduce the information of the most recent product, for example by only keeping a subset of the Landsat-8 bands that matches old imagery. To avoid such loss of information, we propose a new method based on multiband spatial pattern matching. We are focusing on increasing the spectral resolution of archive satellite images to the same level of spectral resolution and coverage as modern imagery. Our method uses analogous scenes taken from modern satellites, which have conceptually the same role as the training images used in multiple-point geostatistics simulation. The spectral characteristics of the training image are then transferred to a target archive image, where new synthetic spectral bands are generated. A spatial pattern matching procedure is used to control this transfer, resulting in preservation of spatial and spectral coherence in the results. We illustrate the methodology on Landsat 8 and Corona imagery. The proposed method was benchmarked against other state-of-the-art colorization techniques, and it shows globally better results.

Perspective: Preservation of coherence in photophysical processes.

Coherence is one of the most important phenomena in ultrafast sciences. We give our perspective on the terminology, observation, and preservation of coherence in photophysical processes with some glimpses to the past and some looking-head to what may pave the way for scaling one of the last bastions in ultrafast science, namely, that of mode specific chemistry where it will be possible to break any specific bond by tailoring the pulse, an accomplishment that obviously would be the dream of any chemist.

High-efficiency coherence-preserving harmonic rejection with crystal optics.

This work reports a harmonic-rejection scheme based on the combination of Si(111) monochromator and Si(220) harmonic-rejection crystal optics. This approach is of importance to a wide range of X-ray applications in all three major branches of modern X-ray science (scattering, spectroscopy, imaging) based at major facilities, and especially relevant to the capabilities offered by the new diffraction-limited storage rings. It was demonstrated both theoretically and experimentally that, when used with a synchrotron undulator source over a broad range of X-ray energies of interest, the harmonic-rejection crystals transmit the incident harmonic X-rays on the order of 10-6. Considering the flux ratio of fundamental and harmonic X-rays in the incident beam, this scheme achieves a total flux ratio of harmonic radiation to fundamental radiation on the order of 10-10. The spatial coherence of the undulator beam is preserved in the transmitted fundamental radiation while the harmonic radiation is suppressed, making this scheme suitable not only for current third-generation synchrotron sources but also for the new diffraction-limited storage rings where coherence preservation is an even higher priority. Compared with conventional harmonic-rejection mirrors, where coherence is poorly preserved and harmonic rejection is less effective, this scheme has the added advantage of lower cost and footprint. This approach has been successfully utilized at the ultra-small-angle X-ray scattering instrument at the Advanced Photon Source for scattering, imaging and coherent X-ray photon correlation spectroscopy experiments. With minor modification, the harmonic rejection can be improved by a further five orders of magnitude, enabling even more performance capabilities.

POST-NONCLASSICAL MODEL OF SELF-FULFILLMENT SCAENTISTMEDICAL

The main goal of article is to analyze results of theoretical and empirical research of psychological reserve medical scientist self-fulfillment in the logic of postnonclassic methodology.The article presents the results of a study 29t graduate of the Odessa Medical University. Conversation, observation and battery of standardized techniques are used as empirical methods.For mathematical data processing author used statistical program SPSS v.21.64 and factor analysis.Аccording to results of empirical research threefactor model of psychological reserve medical scientist self-fulfillment is proposed. Model consists of individual psychological space factor, which determines the type or phase of self-fulfillment, personality openness factor that determines the form of self-fulfillment, coherence preservation and destruction trends factor, which determines the stage of self-fulfillment. Factor poles provisionally designated as «stability reserve» and «reserve of variability». Special attention is given to the complexity of systemic organization of medical-researcher personality in the context of a dynamic harmony cumulative and dissipative processes, orientation, openness and complexity of systemic organization of medical-researcher personality is proposed as a psychological self-identity reserve indicators.Conclusions are drawn on promising direction to explore the potential reserve and resource reserve of researcher personality.

Coherence and entanglement dynamics of vibrating qubits

We investigate the dynamics of coherence and entanglement of vibrating qubits. Firstly, we consider a single trapped ion qubit inside a perfect cavity and successively we use it to construct a bipartite system made of two of such subsystems, taken identical and noninteracting. As a general result, we find that qubit vibration can lead to prolonging initial coherence in both single-qubit and two-qubit system. However, despite of this coherence preservation, we show that the decay of the entanglement between the two qubits is sped up by the vibrational motion of the qubits. Furthermore, we highlight how the dynamics of photon–phonon correlations between cavity mode and vibrational mode, which may serve as a further useful resource stored in the single-qubit system, is strongly affected by the initial state of the qubit. These results provide new insights about the ability of systems made of moving qubits in maintaining quantum resources compared to systems of stationary qubits.

Efficiency and coherence preservation studies of Be refractive lenses for XFELO application.

Performance tests of parabolic beryllium refractive lenses, considered as X-ray focusing elements in the future X-ray free-electron laser oscillator (XFELO), are reported. Single and double refractive lenses were subject to X-ray tests, which included: surface profile, transmissivity measurements, imaging capabilities and wavefront distortion with grating interferometry. Optical metrology revealed that surface profiles were close to the design specification in terms of the figure and roughness. The transmissivity of the lenses is >94% at 8 keV and >98% at 14.4 and 18 keV. These values are close to the theoretical values of ideal lenses. Images of the bending-magnet source obtained with the lenses were close to the expected ones and did not show any significant distortion. Grating interferometry revealed that the possible wavefront distortions produced by surface and bulk lens imperfections were on the level of ∼λ/60 for 8 keV photons. Thus the Be lenses can be succesfully used as focusing and beam collimating elements in the XFELO.

Detection of coherent electron dynamics in benzene and polycyclic aromatic hydrocarbons by two antiphase pulses: An ab initio study

The coherence of electron dynamics in medium-sized molecules was examined by real-time time-dependent density functional theory calculations coupled with molecular dynamics. We observed laser-pulse-induced oscillation of the dipole and an increase in the potential energy of the molecules studied (benzene, naphthalene, and anthracene). Moreover, the second laser pulse with an antiphase optical field oscillation suppressed the dipole oscillation by interference and reduced the potential energy of the molecules. This interference was not observed in a simulation that freezes ion motion. Thus, the photoinduced coherent beat was maintained for a finite time in large molecules, and here, we discuss the effects of the molecular size and the influence of temperature on the coherence preservation.

Quantum coherence and entanglement preservation in Markovian and non-Markovian dynamics via additional qubits

In this paper, we investigate preservation of quantum coherence of a single-qubit interacting with a zero-temperature thermal reservoir through the addition of noninteracting qubits in the reservoir. Moreover, we extend this scheme to preserve quantum entanglement between two and three distant qubits, each of which interacts with a dissipative reservoir independently. At the long time limit, we obtained analytical expressions for the coherence measure and the concurrence of two and three qubits in terms of the number of additional qubits. It is observed that, by increasing the number of additional qubits in each reservoir, the initial coherence and the respective entanglements are completely protected in both Markovian and non-Markovian regimes. Interestingly, the protection of entanglements occurs even under the individually different behaviors of the reservoirs.

Preservation of quantum coherence under Lorentz boost for narrow uncertainty wave packets

We consider the effect of relativistic boosts on single particle Gaussian wave packets. The coherence of the wave function as measured by the boosted observer is studied as a function of the momentum and the boost parameter. Using various formulations of coherence it is shown that in general the coherence decays with the increase of the momentum of the state, as well as the boost applied to it. Employing a basis-independent formulation, we show however, that coherence may be preserved even for large boosts applied on narrow uncertainty wave packets. Our result is exemplified quantitatively for practically realizable neutron wave functions.

Quantum coherence preservation of atom with a classical driving field under non-Markovian environment**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675115, 11204156, 11574178, 11304179, and 11647172) and the Science and Technology Plan Projects of Shandong University, China (Grant No. J16LJ52).

The exact dynamics of an open quantum system consisting of one qubit driven by a classical driving field is investigated. Our attention is focused on the influences of single- and two-photon excitations on the dynamics of quantum coherence and quantum entanglement. It is shown that the atomic coherence can be improved or even maintained by the classical driving field, the non-Markovian effect, and the atom-reservoir detuning. The interconversion between the atomic coherence and the atom-reservoir entanglement exists and can be controlled by the appropriate conditions. The conservation of coherence for different partitions is explored, and the dynamics of a system with two-photon excitations is different from the case of single- photon excitation.

Markovian evolution of quantum coherence under symmetric dynamics

Both conservation laws and practical restrictions impose symmetry constraints on the dynamics of open quantum systems. In the case of time-translation symmetry, which arises naturally in many physically relevant scenarios, the quantum coherence between energy eigenstates becomes a valuable resource for quantum information processing. In this work, we identify the minimum amount of decoherence compatible with this symmetry for a given population dynamics. This yields a generalization to higher-dimensional systems of the relation ${T}_{2}\ensuremath{\le}2{T}_{1}$ for qubit decoherence and relaxation times. It also enables us to witness and assess the role of non-Markovianity as a resource for coherence preservation and transfer. Moreover, we discuss the relationship between ergodicity and the ability of Markovian dynamics to indefinitely sustain a superposition of different energy states. Finally, we establish a formal connection between the resource-theoretic and the master equation approaches to thermodynamics, with the former being a non-Markovian generalization of the latter. Our work thus brings the abstract study of quantum coherence as a resource towards the realm of actual physical applications.

Undamped trace distance and coherence preservation of quantum bit in photonic crystal

We study the coherence preservation of quantum bit in photonic crystal using input–output trace distance. The input–output trace distance can be extremely short and the information hardly dissipates when the quantum bit frequency lies deep inside the photonic band gap. Different from the behavior in cavities, the undissipated information of the quantum bit can be held in the photonic band gap due to the effective interaction between the quantum bit and photonic crystal. A factor called coherence radius is defined in this paper for evaluating the quantum coherence preservation in photonic crystal, which is straightly linked to the visibility of input–output trace distance and the coherence of quantum states.

Decoherence of Topological Qubit in Linear Motions: Decoherence Impedance, Anti-Unruh and Information Backflow

In this work we study the decoherence of topological qubits in linear motions. The topological qubit is made of two spatially-separated Majorana zero modes which are the edge excitations of Kitaev chain [1]. In a previous work [2], it was shown by one of us and his collaborators that the decoherence of topological qubit is exactly solvable, moreover, topological qubit is robust against decoherence in the super-Ohmic environments. We extend the setup of [2] to consider the effect of motions on the decoherence of the topological qubits. Our results show the thermalization as expected by Unruh effect. Besides, we also find the so-called “anti-Unruh” phenomena which shows the rate of decoherence is anti-correlated with the acceleration in short-time scale. Moreover, we modulate the motion patterns of each Majorana modes and find information backflow and the preservation of coherence even with nonzero accelerations. This is the characteristics of the underlying non-Markovian reduced dynamics. We conclude that he topological qubit is in general more robust against decoherence than the usual qubits, and can be take into serious consideration for realistic implementation to have robust quantum computation and communication. This talk is based on our work in [3].

Coherence and entanglement preservation of frequency-converted heralded single photons

We report on quantum frequency conversion of near-infrared photons from a wave-length of 854 nm to the telecommunication O-band at 1310 nm with 8 % overall conversion efficiency. Entangled photon pairs at 854 nm are generated via type-II spontaneous parametric down conversion. One photon is mixed with a strong pump field in a nonlinear ridge waveguide for its conversion to 1310 nm. We demonstrate preservation of first and second order coherence of the photons in the conversion process. Based on this we infer the coherence function of the two-photon state and compare it with the actual measured one. This measurement demonstrates preservation of time-energy entanglement of the pair. With 88 % visibility we violate a Bell inequality.

Video Decolorization Using Visual Proximity Coherence Optimization.

Video decolorization is to filter out the color information while preserving the perceivable content in the video as much and correct as possible. Existing methods mainly apply image decolorization strategies on videos, which may be slow and produce incoherent results. In this paper, we propose a video decolorization framework that considers frame coherence and saves decolorization time by referring to the decolorized frames. It has three main contributions. First, we define decolorization proximity to measure the similarity of adjacent frames. Second, we propose three decolorization strategies for frames with low, medium, and high proximities, to preserve the quality of these three types of frames. Third, we propose a novel decolorization Gaussian mixture model to classify the frames and assign appropriate decolorization strategies to them based on their decolorization proximity. To evaluate our results, we measure them from three aspects: 1) qualitative; 2) quantitative; and 3) user study. We apply color contrast preserving ratio and C2G-SSIM to evaluate the quality of single frame decolorization. We propose a novel temporal coherence degree metric to evaluate the temporal coherence of the decolorized video. Compared with current methods, the proposed approach shows all around better performance in time efficiency, temporal coherence, and quality preservation.

Microscopic description for the emergence of collective dissipation in extended quantum systems

Practical implementations of quantum technology are limited by unavoidable effects of decoherence and dissipation. With achieved experimental control for individual atoms and photons, more complex platforms composed by several units can be assembled enabling distinctive forms of dissipation and decoherence, in independent heat baths or collectively into a common bath, with dramatic consequences for the preservation of quantum coherence. The cross-over between these two regimes has been widely attributed in the literature to the system units being farther apart than the bath’s correlation length. Starting from a microscopic model of a structured environment (a crystal) sensed by two bosonic probes, here we show the failure of such conceptual relation, and identify the exact physical mechanism underlying this cross-over, displaying a sharp contrast between dephasing and dissipative baths. Depending on the frequency of the system and, crucially, on its orientation with respect to the crystal axes, collective dissipation becomes possible for very large distances between probes, opening new avenues to deal with decoherence in phononic baths.

Effectiveness of oxalic acid treatments for the protection of marble surfaces

Naturally formed rims of calcium oxalates developed on calcareous stones have been recognized as effective protective coatings. Inspired in nature, it has been recently proposed the use of oxalate salts for the protection of stone surfaces via dissolution of the calcitic substrate and the subsequent precipitation of oxalate phases. In contrast, the application of an oxalic acid solution on carbonate stones has been generally avoided due to assumed hazards associated with enhanced substrate dissolution. Nonetheless, it has been reported that coherent oxalate layers and preservation of textural features only occurs at low pH, which could be beneficial from a conservation point of view. Here, the application of oxalic acid treatments on two calcitic and dolomitic Spanish marbles from Macael area has been studied as a means to develop effective oxalate protective coatings. Morphological and compositional analyses show that reacted marble surfaces develop μm-thick calcium or calcium and magnesium oxalate rims on calcitic and dolomitic marble, respectively. The presence of such oxalate layers strongly reduces chemical weathering due to acid dissolution and sulfation, without altering the color of the marble substrates. This protection methodology overcomes the limitations of previous oxalate treatments and may represent a highly efficient conservation methodology.

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating.

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard π/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45° and 135° directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.