Coherent Evolution Research Articles

Popular… to a Point: The Enduring Political Challenges of the Public Option.

Policy Points A decade after failing to make it into the Affordable Care Act, the public option reemerged as a health reform goal at both the national and state levels, with polls reporting strong, bipartisan support. A 2020 poll that probed both support for one public option approach (Medicare "buy-in") and attitudes toward government suggests that differences in these attitudes could plague reform advocates' efforts. Although the COVID-19 pandemic viscerally highlighted the need for a more coherent health care system-including universal coverage-other recent evolutions in the broader US political context could undermine reform.

Evaluation of global teleconnections in CMIP6 climate projections using complex networks

Abstract. In climatological research, the evaluation of climate models is one of the central research subjects. As an expression of large-scale dynamical processes, global teleconnections play a major role in interannual to decadal climate variability. Their realistic representation is an indispensable requirement for the simulation of climate change, both natural and anthropogenic. Therefore, the evaluation of global teleconnections is of utmost importance when assessing the physical plausibility of climate projections. We present an application of the graph-theoretical analysis tool δ-MAPS, which constructs complex networks on the basis of spatio-temporal gridded data sets, here sea surface temperature and geopotential height at 500 hPa. Complex networks complement more traditional methods in the analysis of climate variability, like the classification of circulation regimes or empirical orthogonal functions, assuming a new non-linear perspective. While doing so, a number of technical tools and metrics, borrowed from different fields of data science, are implemented into the δ-MAPS framework in order to overcome specific challenges posed by our target problem. Those are trend empirical orthogonal functions (EOFs), distance correlation and distance multicorrelation, and the structural similarity index. δ-MAPS is a two-stage algorithm. In the first place, it assembles grid cells with highly coherent temporal evolution into so-called domains. In a second step, the teleconnections between the domains are inferred by means of the non-linear distance correlation. We construct 2 unipartite and 1 bipartite network for 22 historical CMIP6 climate projections and 2 century-long coupled reanalyses (CERA-20C and 20CRv3). Potential non-stationarity is taken into account by the use of moving time windows. The networks derived from projection data are compared to those from reanalyses. Our results indicate that no single climate projection outperforms all others in every aspect of the evaluation. But there are indeed models which tend to perform better/worse in many aspects. Differences in model performance are generally low within the geopotential height unipartite networks but higher in sea surface temperature and most pronounced in the bipartite network representing the interaction between ocean and atmosphere.

Quantum-jump analysis of frequency up-conversion amplification without inversion in a four-level scheme

In this work, we use the quantum-jump approach to study light-matter interactions in a four-level scheme giving rise to frequency up-conversion amplification without inversion (AWI). The results obtained apply to the case of neutral Hg vapour where, recently, it has been reported AWI of a probe field in the UV regime, opening the way for lasing without inversion in this range of frequencies. We show that, in this scheme, the key element to obtain maximum amplification is the fulfillment of the three-photon resonance condition, which favors coherent evolution periods associated with the probe field gain. We also investigate the parameter values in order to optimize amplification. The present study extends the theoretical understanding of the underlying mechanisms involved in AWI.

Turtling: a time-aware neural topic model on NIH grant data.

Recent initiatives for federal grant transparency allow direct knowledge extraction from large volumes of grant texts, serving as a powerful alternative to traditional surveys. However, its computational modeling is challenging as grants are usually multifaceted with constantly evolving topics. We propose Turtling, a time-aware neural topic model with three unique characteristics. First, Turtling employs pretrained biomedical word embedding to extract research topics. Second, it leverages a probabilistic time-series model to allow smooth and coherent topic evolution. Lastly, Turtling leverages additional topic diversity loss and funding institute classification loss to improve topic quality and facilitate funding institute prediction. We apply Turtling on publicly available NIH grant text and show that it significantly outperforms other methods on topic quality metrics. We also demonstrate that Turtling can provide insights into research topic evolution by detecting topic trends across decades. In summary, Turtling may be a valuable tool for grant text analysis. Turtling is freely available as an open-source software at https://github.com/aicb-ZhangLabs/Turtling.

Atom-field system: Effects of squeezing and intensity dependent coupling on the quantum coherence and nonclassical properties

Recently, Kumar Gerry et al. [Phys. Rev. A 90, 033427 (2014) https://doi.org/10.1103/PhysRevA.90.033427] studied the coherence control in a six-level atom through solving the Schrödinger equation in the field-interaction representation. In this manuscript, we investigate the interaction between a six-level atomic system (SLAS) and a single-mode field initially prepared in a squeezed coherent state. We extend the Jeans–Cummings model to describe the interaction between the atom and the squeezed field (SF) and the system dynamics. We examine the time evolution of the atomic coherence, non-local correlation, statistical properties within the bipartite system in the presence and absence intensity-dependent coupling (I-DC) for different squeezing regimes of the field.

Coherent excitation energy transfer processes in two-dimensional para-sexiphenyl molecular clusters

Excitation energy transfer is one of the most important factors affecting the applications of para-sexiphenyl devices. The study of exciton dynamics and exciton coherence effect of para-sexiphenyl clusters under external field excitation is important in order to improve the performance of molecular devices composed of para-sexiphenyl and its related derivatives. In this work, the two-dimensional disc-like para-sexiphenyl molecular cluster is used as the object of study. The molecular system is simplified into a two-level model based on its structural features and energy level distribution. Within the framework of density matrix theory, the exciton dynamics and exciton coherence behavior of disk-like para-hexaphene molecular clusters excited by different pulse fields are analyzed through using the mathematical mean value approximation of the operator. The results show that when long pulses are used to excite para-sexiphenyl clusters, the single exciton state characteristic appears and is insensitive to the change of excited external field strength. When the clusters are subjected to strong pulsed fields with short pulse widths, multiple excitons are excited simultaneously in the cluster, forming multiple exciton states, with the exciton energy levels shifting toward lower energy and new hybrid states appearing. In the optical response spectrum, there appear multiple resonance peaks. And as the pulse field is enhanced, the multi-exciton effect becomes apparent and the hybridization energy level increases. Under short pulse excitation, the excited states are distributed differently in different energy regions, but all of them show obvious symmetry. As the highest-energy exciton states of H-type clusters are preferentially excited, we analyze the exciton state population and the exciton coherence evolution with time in the high-energy exciton state. With the pulse field increases, Rabi oscillations appear and the exciton coherence effect increases. When the pulsed field reaches a certain field strength, the exciton oscillation cooperativity disappears in the first 100 fs, showing the non-local characteristic. The position of the wave trough of the exciton state population corresponds to the peak in the exciton coherence size. It indicates that when the pulse field is intense enough, a large number of molecules are in the exciton coherent state during the pulsed excitation, and transient out-of-domain phenomena occur.

Experimental demonstration on quantum coherence evolution of two-mode squeezed state

As one of the most remarkable features of quantum mechanics, quantum coherence is regarded as an important quantum resource in the quantum information processing. The one-mode squeezed state and the two-mode squeezed state (Einstein-Podolsky-Rosen (EPR) entangled states) as the most representative examples of nonclassical states both have quantum coherence. The squeezing property of the squeezed state is described by the variance of quadrature components, and the positive partial transposition (PPT) criterion is used to describe the entanglement of the EPR entangled states. The research of the quantum coherence of Gaussian states is also a bridge between the properties of squeezing and entanglement. It has been shown that the quantum coherence with infinite-dimensional systems can be quantified by relative entropy. One of the widely used effective methods to obtain the value of quantum coherence experimentally is the quantum tomography. The covariance matrices of the quantum states are reconstructed via balanced homodyne detection and then taken into quantum coherence expression to calculate the corresponding value. The main factors affecting quantum coherence are the classical and uncorrelated noise in the actual experimental generation processing and the decoherence effect caused by the coupling between quantum resources and the surrounding environment. And the quantum coherence evolution in the generation and transmission process of the quantum resources is essential for the practical applications. Therefore, we analyze in detail the influences of the impurity of quantum resource on squeezing, entanglement and quantum coherence. The evolutions of quantum coherence of these Gaussian states in the lossy channels are demonstrated experimentally. The quantum coherence is shown to be robust against the loss in the lossy channels, which is similar to the case of squeezing and entanglement. The quantum coherences of the squeezed states and the EPR entangled states are robust against the thermal photons in the actual experimental generation processing, although the squeezing and entanglement of Gaussian states disappear at a certain number of thermal photons. Our research results provide a reference for the practical applications of quantum coherence of the squeezed state and entangled states in the lossy environment.

Robustness of energy landscape control to dephasing

Abstract As shown in previous work, in some cases closed quantum systems exhibit a non-conventional absence of trade-off between performance and robustness in the sense that controllers with the highest fidelity can also provide the best robustness to parameter uncertainty. As the dephasing induced by the interaction of the system with the environment guides the evolution to a more classically mixed state, it is worth investigating what effect the introduction of dephasing has on the relationship between performance and robustness. In this paper we analyze the robustness of the fidelity error, as measured by the logarithmic sensitivity function, to dephasing processes. We show that introduction of dephasing as a perturbation to the nominal unitary dynamics requires a modification of the log-sensitivity formulation used to measure robustness about an uncertain parameter with nonzero nominal value used in previous work. We consider controllers optimized for a number of target objectives ranging from fidelity under coherent evolution to fidelity under dephasing dynamics to determine the extent to which optimizing for a specific regime has desirable effects in terms of robustness. Our analysis is based on two independent computations of the log-sensitivity: a statistical Monte Carlo approach and an analytic calculation. We show that despite the different log-sensitivity calculations employed in this study, both demonstrate that the log-sensitivity of the fidelity error to dephasing results in a conventional trade-off between performance and robustness.

Coherent interaction-free detection of microwave pulses with a superconducting circuit

The interaction-free measurement is a fundamental quantum effect whereby the presence of a photosensitive object is determined without irreversible photon absorption. Here we propose the concept of coherent interaction-free detection and demonstrate it experimentally using a three-level superconducting transmon circuit. In contrast to standard interaction-free measurement setups, where the dynamics involves a series of projection operations, our protocol employs a fully coherent evolution that results, surprisingly, in a higher probability of success. We show that it is possible to ascertain the presence of a microwave pulse resonant with the second transition of the transmon, while at the same time avoid exciting the device onto the third level. Experimentally, this is done by using a series of Ramsey microwave pulses coupled into the first transition and monitoring the ground-state population.

Super-resolved time–frequency measurements of coupled phonon dynamics in a 2D quantum material

Methods to probe and understand the dynamic response of materials following impulsive excitation are important for many fields, from materials and energy sciences to chemical and neuroscience. To design more efficient nano, energy, and quantum devices, new methods are needed to uncover the dominant excitations and reaction pathways. In this work, we implement a newly-developed superlet transform—a super-resolution time-frequency analytical method—to analyze and extract phonon dynamics in a laser-excited two-dimensional (2D) quantum material. This quasi-2D system, 1T-TaSe2, supports both equilibrium and metastable light-induced charge density wave (CDW) phases mediated by strongly coupled phonons. We compare the effectiveness of the superlet transform to standard time-frequency techniques. We find that the superlet transform is superior in both time and frequency resolution, and use it to observe and validate novel physics. In particular, we show fluence-dependent changes in the coupled dynamics of three phonon modes that are similar in frequency, including the CDW amplitude mode, that clearly demonstrate a change in the dominant charge-phonon couplings. More interestingly, the frequencies of the three phonon modes, including the strongly-coupled CDW amplitude mode, remain time- and fluence-independent, which is unusual compared to previously investigated materials. Our study opens a new avenue for capturing the coherent evolution and couplings of strongly-coupled materials and quantum systems.

Signatures of a quantum stabilized fluctuating phase and critical dynamics in a kinetically constrained open many-body system with two absorbing states

We introduce and investigate an open many-body quantum system in which kinetically constrained coherent and dissipative processes compete. The form of the incoherent dissipative dynamics is inspired by that of epidemic spreading or cellular-automaton-based computation related to the density-classification problem. It features two non-fluctuating absorbing states as well as a $\mathcal{Z}_2$-symmetric point in parameter space. The coherent evolution is governed by a kinetically constrained $\mathcal{Z}_2$-symmetric many-body Hamiltonian which is related to the quantum XOR-Fredrickson-Andersen model. We show that the quantum coherent dynamics can stabilize a fluctuating state and we characterize the transition between this active phase and the absorbing states. We also identify a rather peculiar behavior at the $\mathcal{Z}_2$-symmetric point. Here the system approaches the absorbing-state manifold with a dynamics that follows a power-law whose exponent continuously varies with the relative strength of the coherent dynamics. Our work shows how the interplay between coherent and dissipative processes as well as symmetry constraints may lead to a highly intricate non-equilibrium evolution and may stabilize phases that are absent in related classical problems.

Markovian and non-Markovian dynamics of quantum coherence in the extended XX chain

The Markovian and non-Markovian dynamics of quantum coherence, including single-spin coherence, two-spin coherence, and its distribution (collective and localized coherence), are investigated in the $XX$ spin chain with three-spin interaction. We find that the single-spin and localized coherence do not decrease but increase with time, which makes the dynamic evolution of the two-spin coherence more robust than entanglement and quantum discord. The three-spin interaction can lower the values of quantum coherence in Markovian evolution and heighten the oscillation frequency of quantum coherence in non-Markovian evolution because it can speed up the flow of coherence information. Finally, the trade-off relation between the collective and the localized coherence is clearly shown in their dynamic evolution. Thanks to the coherence trade-off, we find the substitution of localized coherence for collective coherence in dominating the dynamics of the two-spin coherence.

Coherent and Dephasing Spectroscopy for Single-Impurity Probing of an Ultracold Bath.

We report Ramsey spectroscopy on the clock states of individual Cs impurities immersed in an ultracold Rb bath. We record both the interaction-driven phase evolution and the decay of fringe contrast of the Ramsey interference signal to obtain information about bath density or temperature nondestructively. The Ramsey fringe is modified by a differential shift of the collisional energy when the two Cs states superposed interact with the Rb bath. This differential shift is directly affected by the mean gas density and the details of the Rb-Cs interspecies scattering length, affecting the phase evolution and the contrast of the Ramsey signal. Additionally, we enhance the temperature dependence of the phase shift preparing the system close to a low-magnetic-field Feshbach resonance where the s-wave scattering length is significantly affected by the collisional (kinetic) energy. Analyzing coherent phase evolution and decay of the Ramsey fringe contrast, we probe the Rb cloud's density and temperature. Our results point at using individual impurity atoms as nondestructive quantum probes in complex quantum systems.

Coherent quantum annealing in a programmable 2,000 qubit Ising chain

Quantum simulation has emerged as a valuable arena for demonstrating and understanding the capabilities of near-term quantum computers1,2,3. Quantum annealing4,5 has been successfully used in simulating a range of open quantum systems, both at equilibrium6,7,8 and out of equilibrium9,10,11. However, in all previous experiments, annealing has been too slow to coherently simulate a closed quantum system, due to the onset of thermal effects from the environment. Here we demonstrate coherent evolution through a quantum phase transition in the paradigmatic setting of a one-dimensional transverse-field Ising chain, using up to 2,000 superconducting flux qubits in a programmable quantum annealer. In large systems, we observe the quantum Kibble–Zurek mechanism with theoretically predicted kink statistics, as well as characteristic positive kink–kink correlations, independent of temperature. In small chains, excitation statistics validate the picture of a Landau–Zener transition at a minimum gap. In both cases, the results are in quantitative agreement with analytical solutions to the closed-system quantum model. For slower anneals, we observe anti-Kibble–Zurek scaling in a crossover to the open quantum regime. The coherent dynamics of large-scale quantum annealers demonstrated here can be exploited to perform approximate quantum optimization, machine learning and simulation tasks.

Effective Hamiltonian and spin dynamics in fast MAS TRAPDOR-HMQC experiments involving spin-3/2 quadrupolar nuclei

We present a theoretical and numerical description of the spin dynamics associated with TRAPDOR-HMQC (T-HMQC) experiment for a 1H (I) – 35Cl (S) spin system under fast magic angle spinning (MAS). Towards this an exact effective Hamiltonian describing the system is numerically evaluated with matrix logarithm approach. The different magnitudes of the heteronuclear and pure S terms in the effective Hamiltonian allow us to suggest a truncation approximation, which is shown to be in excellent agreement with the exact time evolution. Limitations of this approximation, especially at the rotary resonance condition, are discussed. The truncated effective Hamiltonian is further employed to monitor the buildup of various coherences during TRAPDOR irradiation. We observe and explain a functional resemblance between the magnitude of different terms in the truncated effective Hamiltonian and the amplitudes of various coherences during TRAPDOR irradiation, as function of crystallite orientation. Subsequently, the dependence of the sign (phase) of the T-HMQC signal on the coherence type generated is investigated numerically and analytically. We examine the continuous creation and evolution of various coherences at arbitrary times, i.e., at and between avoided level crossings. Behavior between consecutive crossings is described analytically and reveals ‘quadrature’ evolution of pairs of coherences and coherence interconversions. The adiabatic, sudden, and intermediate regimes for T-HMQC experiments are discussed within the approach established by A. J. Vega. Equations as well as numerical simulations suggest the existence of a driving coherence which builds up between consecutive crossings and then gets distributed at crossings among other coherences. In the intermediate regime, redistribution of the driving coherence to other coherences is almost uniform such that coherences involving S-spin double-quantum terms may be efficiently produced.

A critical content-analysis of sustainable supplier development literature and future research directions

Sustainable supplier development (SSD) deals with how partner firms help their suppliers improve sustainable performance. Recently, SSD has received increased attention in academia and practice. In line with the emergence of supply chain sustainability , SSD evolved from being a primarily environmental perspective to a perspective incorporating corporate social responsibility and business ethics, and eventually a holistic sustainability perspective. This evolution led to a gap in theory as to the lack of a clear boundary between SSD and other sustainable supplier management practices, and a gap in practice on understanding how such practices help buying firms improve their supplier sustainability capabilities. A content-analysis based literature review is used to develop a framework for understanding the foundations of past research to address the above two important concerns and to come up with promising avenues for future research. For this purpose, a total of 47 SSD articles published in recognized academic journals during the decade 2010–2021 (August) are selected, categorized, analyzed and identified to highlight the current research status and opportunities. This article introduces a structural framework to critically examine past articles within four categories – concepts, practices, problems and solutions. The framework provides a general roadmap for future research opportunities. The review presented offers academicians and practitioners a better understanding of SSD towards a more coherent evolution of future research and practice in this area.

Experimental verification of a coherence factorization law for quantum states

As a quantum resource, quantum coherence plays an important role in modern physics. Many coherence measures and their relations with entanglement have been proposed, and the dynamics of entanglement has been experimentally studied. However, the knowledge of general results for coherence dynamics in open systems is limited. Here we propose a coherence factorization law that describes the evolution of coherence passing through any noisy channels characterized by genuinely incoherent operations. We use photons to implement the quantum operations and experimentally verify the law for qubits and qutrits. Our work is a step toward understanding of the evolution of coherence when the system interacts with the environment, and will boost the study of more general laws of coherence.

The role of Heisenberg spin exchange and the quantum Zeno effect in the spin-selective reaction between spin-1/2 and spin-1 particles.

The kinetics of spin-selective reactions involving triplet molecules, such as triplet-triplet annihilation or electron transfer to dioxygen molecules in the ground triplet spin state, are strongly dependent on the dipole-dipole interaction (DDI) of electron spins in spin-1 particles. The effect of this interaction on the intersystem crossing in the reaction encounter complex of the paramagnetic particles was previously considered for some particular cases using oversimplified approaches. In this study, we consider a rigorous kinetic model of the irreversible reaction between the spin-1/2 and spin-1 particles in an encounter complex with the reactive doublet state. This model explicitly includes both isotropic exchange coupling of the reactants and spin dependence of the reaction rate in the form of the Haberkorn reaction term. For the time-independent DDI, an analytical expression for the reaction kinetics was derived. The effect of DDI fluctuations was analyzed using numerical simulations. It was found that increasing both the exchange coupling and the reaction rate constants can significantly slow down the quartet-doublet spin transitions and, as a consequence, the observed spin-selective reaction rate. Additionally, the presence of the irreversible reaction in the doublet states affects a coherent evolution in the non-reactive quartet subsystem.

Quantum coherence and parameter estimation for mixed entangled coherent states

We study the temporal evolution of quantum coherence and parameter estimation for two-mode coherent-state superposition by using the master equation. Analytic expressions are provided and numerically displayed, which can illustrate the reliance of the coherence and Fisher information during the dynamics. Generally, we find that the amount of the quantum measures has the same behavior during the time variation, and displays a different order that depends on the different strength regimes of the input radiation fields and then disappears at infinite times. We show that these measures start from maximal value at the initial instant and decrease the time goes on. Moreover, we can observe that these measures can be protected resisted from the environment effect during the dynamics, showing an important feature of coherence and Fisher information. The obtained results can be assumed more practical in the characterization of the behavior of the coherence and Fisher information under the effect of the environment. Our observations can provide significant implications in harnessing these phenomena in quantum optics and information.

Low-spatial coherence vortex beam generation by random distributed feedback fibre laser

Vortex beams with low spatial coherence have great potential in applications such as imaging, medical diagnosis, optical communication, and manipulation. In this study, we experimentally demonstrated a radially polarised vortex beam with extremely low spatial coherence using a random distributed feedback fibre laser (RDFB-FL). The results show that the spatial coherence of vortex beams can be reduced in an RDFB-FL and further reduced by introducing radial polarisation. In addition, the evolution of the spatial coherence of a RDFB-FL-generated vortex beam with varying pump power was clearly revealed for the first time. The spatial coherence first decreases sharply up to a point as the pump power increases and then remains constant, and this behaviour is quite different from that of vortex beams generated by conventional fibre lasers. The present study provides an effective method for achieving a low-spatial coherence vortex beam source for application in telecommunications and imaging systems.