Coherent Contributions Research Articles

Direct numerical simulation of turbulent pipe flow by large-scale control using buoyancy force

Skin-friction drag reduction control for a fully developed turbulent pipe flow is performed using direct numerical simulations. Heating and cooling of pipe wall is homogeneous in the streamwise direction and varies in the azimuthal direction and buoyancy force induces the flow to decrease the skin-friction drag. The control parameters are the amplitude of buoyancy force and wavenumber of heating and cooling in the azimuthal direction. There are two different mechanisms of skin-friction drag reduction: stable stratification and large-scale vortical structure. In the former, the buoyancy force attenuates the turbulence directly. In the latter, the buoyancy force creates wall jets along the pipe wall, and a large-scale streamwise vortex is formed. The vortex increases the coherent contribution to the skin-friction coefficient, but it reduces the random contribution indirectly.

Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors.

We have previously demonstrated that in the context of two-dimensional (2D) coherent electronic spectroscopy measured by phase modulation and phase-sensitive detection, an incoherent nonlinear response due to pairs of photoexcitations produced via linear excitation pathways contributes to the measured signal as an unexpected background [Grégoire et al., J. Chem. Phys. 147, 114201 (2017)]. Here, we simulate the effect of such incoherent population mixing in the photocurrent signal collected from a GaAs solar cell by acting externally on the transimpedance amplifier circuit used for phase-sensitive detection, and we identify an effective strategy to recognize the presence of incoherent population mixing in 2D data. While we find that incoherent mixing is reflected by the crosstalk between the linear amplitudes at the two time-delay variables in the four-pulse excitation sequence, we do not observe any strict phase correlations between the coherent and incoherent contributions, as expected from modeling of a simple system.

Generalized Resonance Energy Transfer Theory: Applications to Vibrational Energy Flow in Optical Cavities.

A general rate theory for resonance energy transfer (gRET) is formulated to incorporate any degrees of freedom (e.g., rotation, vibration, exciton, and polariton) as well as coherently coupled composite donor or acceptor states. The compact rate expression allows us to establish useful relationships: (i) detailed balance condition when the donor and acceptor are at the same temperature; (ii) proportionality to the product of dipole correlation tensors, which is not necessarily equivalent to spectral overlap; (iii) scaling with the effective coherent size, i.e., the number of coherently coupled molecules or modes; (iv) decomposition of collective rate in homogeneous systems into the monomer and coherence contributions such that the ratio of the two defines the quantum enhancement factor F; (v) spatial and orientational dependences as derived from the interaction potential. For the special case of exciton transfer, the general rate formalism reduces to FRET or its multichromophoric extension. When applied to cavity-assisted vibrational energy transfer between molecules or within a molecule, the general rate expression provides an intuitive explanation of intriguing phenomena such as cooperativity, resonance, and nonlinearity in the collective vibrational strong coupling (VSC) regime, as demonstrated in recent simulations. The relevance of gRET to cavity-catalyzed reactions and intramolecular vibrational redistribution is discussed and will lead to further theoretical developments.

Assessment of interferometric coherence contribution to corn and soybean mapping with Sentinel-1 data time series

This work aims to evaluate the added value of interferometric coherence to backscatter information of Synthetic Aperture Radar (SAR) systems for soybean and corn mapping. First, SAR response to crop growth, and then accuracies for the classification using a combination of SAR variables were evaluated for scenarios that employ in-season or the entire season time series. Results showed that: i) using a single feature, the backscatter at vertical-horizontal (VH) polarization would be the most suitable variable; ii) the complementarity of coherence to single backscatter at vertical-vertical (VV) polarization was demonstrated, adding a significant contribution to late sown corns differentiation and iii) the combination of VV and VH backscatter would be the preferable variables for the proposed classification. In this case, the adding of coherence did not show a significant accuracy improvement, while a high computational cost is required. Finally, high general accuracies (until 90%) for early-season maps were achieved.

Time-Evolving Quantum Superpositions in Open Systems and the Rich Content of Coherence Maps.

We discuss the general features of the time-evolving reduced density matrix (RDM) of multistate systems coupled to dissipative environments and show that many important aspects of the dynamics are visualized effectively and transparently through coherence maps, defined as snapshots of the real and imaginary components of the RDM on the square grid of system sites. In particular, the spread, signs, and shapes of the coherence maps collectively characterize the state of the system and the nature of the dynamics, as well as the equilibrium state. The topology of the system is readily reflected in its coherence map. Rows and columns show the composition of quantum superpositions, and their filling indicates the extent of the surviving coherence. Linear combinations of imaginary RDM elements specify instantaneous population derivatives. The main diagonal comprises the incoherent component of the dynamics, while the upper/lower triangular areas give rise to coherent contributions that increase the purity of the RDM. In open systems, the coherence map evolves to a band surrounding the principal diagonal whose width decreases with increasing temperature and dissipation strength. We illustrate these behaviors with examples of 10-site model molecular aggregates with Frenkel exciton couplings, where the electronic states of each monomer are coupled to harmonic vibrational baths.

Severe and moderately severe acute pancreatits: is the separation before 48 hours possible?

We present the first determination of the energy-dependent amplitudes of N⁎ resonances extracted from their decay in KΛ pairs in p+p→pK+Λ reactions. A combined Partial Wave Analysis of seven data samples with exclusively reconstructed p+p→pK+Λ events measured by the COSY-TOF, DISTO, FOPI and HADES Collaborations in fixed target experiments at kinetic energies between 2.14 to 3.5 GeV is used to determine the amplitude of the resonant and non-resonant contributions into the associated strangeness final state. The contribution of seven N⁎ resonances with masses between 1650 MeV/c2 and 1900 MeV/c2 for an excess energy between 0 and 600 MeV has been considered. The Σ–p cusp and final state interactions for the p–Λ channel are also included as coherent contributions in the PWA. The N⁎ contribution is found to be dominant with respect to the phase space emission of the pKΛ+ final state at all energies demonstrating the important role played by both N⁎ and interference effects in hadron–hadron collisions.

Probing Atomic ‘Quantum Grating’ by Collisions with Charged Particles

The wave function of an atom, which passed through a diffraction grating, is characterized by a regular space structure. Correspondingly, the interaction of another particle with this atom can be viewed as scattering on an ‘atomic quantum grating’ made of just a single atom. Probing this ‘grating’ by collisions with a charged projectile reveals few-body interference phenomena caused by the coherent contributions of its ‘slits’ to the transition amplitude (the superposition principle) and quantum entanglement of the particles involved. In particular, the spectra of electrons emitted from the atom in collisions with swift ions exhibit a pronounced interference pattern whose shape can be extremely sensitive to the collision velocity.

Connection 100—An Auto-Ethnography of My (Mystical) Connection Experiences

This paper provides an autoethnographic accounting and analysis of my own mystical experiences, called connection experiences in this paper. This account, which is structured around a description of my early experiences, attempts to weave together psychological, sociological, historical, and methodological themes into a coherent contribution that advances our understanding of connection experience. The paper includes an explication of the four stages of the research project that developed as a consequence of these experiences as well as an examination of the processes, tools (i.e., MediWiki), and emotional, psychological, professional, and scholarly challenges of collecting and analyzing the autoethnographic data of mystical experiences. The denouement of the paper is the presentation of a conceptual schema aimed at overcoming nomenclature confusion and providing a basis for description, analysis, and discussion of connection and connection experiences. The utility of the schema is demonstrated when it is used to provide a clear overview of my own connection experiences, and the connection experiences of others. In order to facilitate critical discussion of the conceptual framework, a glossary of terms developed and presented in this paper is provided at the end.

Role of alloying in the phonon and thermal transport of SnS–SnSe across the phase transition

Atomic-level investigations of the underlying phonon and thermal transports of strongly anharmonic alloy-based thermoelectric materials and their structural phase transitions are yet to be fully explored. Herein, we systematically investigate the anharmonic lattice dynamics and thermal transport of SnS0.75Se0.25 using perturbation theory up to quartic anharmonicity and molecular dynamics simulations with the first-principles-based machine-learning potential. We find the non-monotonic temperature dependence of the phonon linewidths and frequencies of the Γ4 and Y1 modes. This work demonstrates an apparent κL reduction from SnS to SnS0.75Se0.25, mainly attributed to the enhanced scattering rates of the middle-frequency phonons and the decreased group velocities of the high-frequency phonons. We also find that the effects of the quartic anharmonicity on the thermal transport of SnS and SnS0.75Se0.25 are significant, and the phonon coherence contributions are non-negligible in describing the thermal transport. Moreover, we reveal a decrease of κL in SnS0.75Se0.25 by randomizing Se atoms, which can be ascribed to an additional phonon scattering arising from sublattice mass disorder.

Origin of ultralow phonon transport and strong anharmonicity in lead-free halide perovskites

All-inorganic lead-free halide double perovskites offer a promising avenue toward non-toxic, stable optoelectronic materials, properties that are missing in their prominent lead-containing counterparts. Their large thermopowers and high carrier mobilities also make them promising for thermoelectric applications. Here, we present a first-principles study of the lattice vibrations and thermal transport behaviors of Cs2SnI6 and γ-CsSnI3, two prototypical compounds in this materials class. We show that conventional static zero temperature density functional theory (DFT) calculations severely underestimate the lattice thermal conductivities (κl) of these compounds, indicating the importance of dynamical effects. By calculating anharmonic renormalized phonon dispersions, we show that some optic phonons significantly harden with increasing temperature (T), which reduces the scattering of heat carrying phonons and enhances calculated κl values when compared with standard zero temperature DFT. Furthermore, we demonstrate that coherence contributions to κl, arising from wave like phonon tunneling, are important in both compounds. Overall, calculated κl with temperature-dependent interatomic force constants, built from particle and coherence contributions, are in good agreement with available measured data, for both magnitude and temperature dependence. Large anharmonicity combined with low phonon group velocities yield ultralow κl values, with room temperature values of 0.26 W/m-K and 0.72 W/m-K predicted for Cs2SnI6 and γ-CsSnI3, respectively. We further show that the lattice dynamics of these compounds are highly anharmonic, largely mediated by rotation of the SnI6 octahedra and localized modes originating from Cs rattling motion. These thermal characteristics combined with their previously computed excellent electronic properties make these perovskites promising candidates for optoelectronic and room temperature thermoelectric applications.

Experimental demonstration of the dynamics of quantum coherence evolving under a PT-symmetric Hamiltonian on an NMR quantum processor

In this work, we study the dynamics of quantum coherence (total coherence, global coherence and local coherence) evolving under a local PT-symmetric Hamiltonian in maximally entangled bipartite and tripartite states. Our results indicate that quantum coherence in the bipartite state oscillates in the unbroken phase regime of the PT-symmetric Hamiltonian. Interestingly, in the broken phase regime, while the global coherence decays exponentially, the local and total coherences enter a “freezing” regime where they attain a stable value over time. A similar pattern is observed for the dynamics of total and local coherences in the maximally entangled tripartite state, while the dynamics of global coherence in this state differs from that of the bipartite state. Our study provides some novel insights into the independent contributions of global and local coherence to the freezing and oscillatory behavior of the total quantum coherence in both the unbroken and the broken phases, respectively. These results were experimentally validated for a maximally entangled bipartite state on a three-qubit nuclear magnetic resonance (NMR) quantum processor, with one of the qubits acting as an ancilla. The experimental results match well with the theoretical predictions, up to experimental errors.

Effects of high-order anharmonicity on anomalous lattice dynamics and thermal transport in fully filled skutterudite YbFe4Sb12

Accurately describing the lattice dynamics and microscopic mechanism of thermal transport in materials with low-lying flat phonon modes remains an outstanding challenge due to the intrinsic strong anharmonicity. In this paper, we investigate the lattice dynamics and thermal transport in skutterudite ${\mathrm{YbFe}}_{4}{\mathrm{Sb}}_{12}$ using a state-of-the-art first-principles-based anharmonic phonon renormalization technique and a unified theory of lattice thermal transport. In contrast to the previous phenomenological models that introduce additional resonant scattering terms or hopping channels, we show that the unusual total lattice thermal conductivity in ${\mathrm{YbFe}}_{4}{\mathrm{Sb}}_{12}$ can be accurately predicted by considering anharmonic phonon renormalization and coherence contributions from the off-diagonal terms of heat flux operators. Both the cubic and quartic anharmonicities are essential for precisely predicting the significant shift in phonon energies. Specifically, the anharmonicity-induced phonon stiffening of the low-lying flat modes significantly enhances the thermal conductivity of particlelike phonons, e.g., by up to a factor of 1.6 at 300 K, by suppressing the cubic coupling strength and altering the scattering phase space, resulting in much-improved agreement with experiments. By further including the coherence contributions, the predicted total thermal conductivity increases by \ensuremath{\sim}22% throughout the entire temperature range, reproducing well the experimental values in both magnitude and temperature dependence. In this paper, we highlight the strong impact of higher-order anharmonicity on lattice dynamics and thermal transport in the filled skutterudite ${\mathrm{YbFe}}_{4}{\mathrm{Sb}}_{12}$. The insights gained in this paper will be helpful for manipulating the thermal properties of skutterudites and potentially other complex materials with strong anharmonicity, which can improve their performance in applications such as thermoelectrics, ferroelectrics, and photovoltaics.

Pushing multiphoton resonant ionization of the argon atom to the low-intensity regime

Resonance-enhanced multiphoton ionization process of the argon atom by an 800-nm 30-fs linearly polarized laser field is investigated at intensities range from 1.1 to $4.55\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. At $4.55\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ intensity the experimental photoelectron energy spectrum is in a good agreement with the time-dependent Schr\"odinger equation (TDSE) calculation where the double structure originating from dressed $4p\ensuremath{-}4d$ coupled transition is clearly identified. At lower intensity of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$, the resonant ionization process via the $4f$ state is observed, however, the expected peak (jet) at ${90}^{\ensuremath{\circ}}$ in the photoelectron angular distribution from the zeroth order above threshold ionization, has vanished completely. Such behavior is attributed to the destructive interference phenomenon in the coherent contributions of different partial waves of the photoelectron, namely, $\ensuremath{\epsilon}d$ and $\ensuremath{\epsilon}g$ states, and has been confirmed in our TDSE calculations.

Discrimination of coherent and incoherent cathodoluminescence using temporal photon correlations

We present a method to separate coherent and incoherent contributions of cathodoluminescence (CL) by using a time-resolved coincidence detection scheme. For a proof-of-concept experiment, we generate CL by irradiating an optical multimode fiber with relativistic electrons in a transmission electron microscope. A temporal analysis of the CL reveals a large peak in coincidence counts for small time delays, also known as photon bunching. Additional measurements allow us to attribute the bunching peak to the temporal correlations of coherent CL (Cherenkov radiation) created by individual electrons. Thereby, we show that coincidence measurements can be employed to discriminate coherent from incoherent CL and to quantify their contribution to the detected CL signal. This method provides additional information for the correct interpretation of CL, which is essential for material characterization. Furthermore, it might facilitate the study of coherent electron–matter interaction.

Work and Fluctuations: Coherent vs. Incoherent Ergotropy Extraction

We consider a quasi-probability distribution of work for an isolated quantum system coupled to the energy-storage device given by the ideal weight. Specifically, we analyze a trade-off between changes in average energy and changes in weight's variance, where work is extracted from the coherent and incoherent ergotropy of the system. Primarily, we reveal that the extraction of positive coherent ergotropy can be accompanied by the reduction of work fluctuations (quantified by a variance loss) by utilizing the non-classical states of a work reservoir. On the other hand, we derive a fluctuation-decoherence relation for a quantum weight, defining a lower bound of its energy dispersion via a dumping function of the coherent contribution to the system's ergotropy. Specifically, it reveals that unlocking ergotropy from coherences results in high fluctuations, which diverge when the total coherent energy is unlocked. The proposed autonomous protocol of work extraction shows a significant difference between extracting coherent and incoherent ergotropy: The former can decrease the variance, but its absolute value diverges if more and more energy is extracted, whereas for the latter, the gain is always non-negative, but a total (incoherent) ergotropy can be extracted with finite work fluctuations. Furthermore, we present the framework in terms of the introduced quasi-probability distribution, which has a physical interpretation of its cumulants, is free from the invasive nature of measurements, and reduces to the two-point measurement scheme (TPM) for incoherent states. Finally, we analytically solve the work-variance trade-off for a qubit, explicitly revealing all the above quantum and classical regimes.

Anharmonicity-induced phonon hardening and phonon transport enhancement in crystalline perovskite BaZrO3

We investigated the effects of cubic and quartic anharmonicity on lattice dynamics and thermal transport in highly anharmonic ${\mathrm{BaZrO}}_{3}$ crystal over a wide temperature range (300--2000 K) by combining the first-principles-based self-consistent phonon theory and a unified theory of thermal transport including population and coherence contributions. By considering the effects from bubble and loop diagrams, the contributions of both three-phonon (3ph) and four-phonon (4ph) interaction processes to phonon scattering rates and energy shifts were clarified. Anharmonic phonon renormalization is found to play a crucial role in determining the finite-temperature phonon energies and lattice thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{L}}$ in ${\mathrm{BaZrO}}_{3}$. Specifically, the lattice anharmonicity induces significant low-frequency optical phonon hardening at elevated temperatures, which is correlated with the U-shaped potential energy surfaces for these modes. The low-frequency optical phonon hardening significantly suppresses phonon scattering rates by altering the phonon weighted phase space of both 3ph and 4ph interaction processes, thereby leading to significant enhancement in the ${\ensuremath{\kappa}}_{\mathrm{L}}$ and weaker temperature dependence of ${\ensuremath{\kappa}}_{L}\ensuremath{\sim}{T}^{\ensuremath{-}0.75}$ than traditional harmonic treatments. Moreover, although the coherent thermal transport channel is suppressed by anharmonic phonon renormalization, it is enhanced by the 4ph scattering processes. The coherence contribution becomes nonnegligible at elevated temperatures and may contribute up to 17.38% of the total ${\ensuremath{\kappa}}_{\mathrm{L}}$ at 1500 K. In this paper, we highlight the strong influence of the lattice anharmonicity on thermal conductivity in severely anharmonic systems and the importance of coherent thermal transport channel at elevated temperatures.

Wavelet analysis of high-speed transition and turbulence over a flat surface

This paper presents a study of high speed boundary layers using the wavelet method. We analyze direct numerical simulation data for high-speed, compressible transitional, and turbulent boundary layer flows using orthogonal anisotropic wavelets. The wavelet-based method of extraction of coherent structures is applied to the flow vorticity field, decomposed into coherent and incoherent contributions using thresholding of the wavelet coefficients. We show that the coherent parts of the flow, enstrophy spectra, are close to the statistics of the total flow, and the energy of the incoherent, noise-like background flow is equidistributed. Furthermore, we investigate the distribution of the incoherent vorticity in the transition and turbulent regions and examine the correlation with the near-wall pressure fluctuations. The results of our analysis suggest that the incoherent vorticity part is not a random “noise” and correlates with the actual noise emanating from inside the boundary layer. This could have implications regarding our understanding of the physics of compressible boundary layers and the development of engineering models.

Coherent contributions to population dynamics in a semiconductor microcavity

Multidimensional coherent spectroscopy (MDCS) is used to separate coherent and incoherent nonlinear contributions to the population-time dynamics in a GaAs-based semiconductor microcavity encapsulating a single InGaAs quantum well. In a three-pulse four-wave-mixing scheme, the second delay time is the population time that in MDCS probes excited-state coherences and population dynamics. Nonlinear optical interactions can mix these contributions, which are isolated here for the lower- and upper-exciton polariton through the self- and mutual-interaction features. Results show fast decays and oscillations arising from the coherent response, including a broad stripe along the absorption energy axis, and longer time mutual-interaction features that do not obey a simple population decay model. These results are qualitatively replicated by Bloch equation simulations for the $1s$ exciton strongly coupled to the intracavity field. The simulations allow for separation of coherent and incoherent Pauli-blocking and Coulomb interaction terms within the ${\ensuremath{\chi}}^{(3)}$-limit, and a direct comparison of each feature in one-quantum rephasing and zero-quantum spectra.

Unifying Quantum and Classical Speed Limits on Observables

The presence of noise or the interaction with an environment can radically change the dynamics of observables of an otherwise isolated quantum system. We derive a bound on the speed with which observables of open quantum systems evolve. This speed limit divides into Mandalestam and Tamm's original time-energy uncertainty relation and a time-information uncertainty relation recently derived for classical systems, generalizing both to open quantum systems. By isolating the coherent and incoherent contributions to the system dynamics, we derive both lower and upper bounds to the speed of evolution. We prove that the latter provide tighter limits on the speed of observables than previously known quantum speed limits, and that a preferred basis of \emph{speed operators} serves to completely characterize the observables that saturate the speed limits. We use this construction to bound the effect of incoherent dynamics on the evolution of an observable and to find the Hamiltonian that gives the maximum coherent speedup to the evolution of an observable.

Experiential appreciation as a pathway to meaning in life.

A key research program within the meaning in life (MIL) literature aims to identify the key contributors to MIL. The experience of existential mattering, purpose in life and a sense of coherence are currently posited as three primary contributors to MIL. However, it is unclear whether they encompass all information people consider when judging MIL. Based on the ideas of classic and contemporary MIL scholars, the current research examines whether valuing one's life experiences, or experiential appreciation, constitutes another unique contributor to MIL. Across seven studies, we find support for the idea that experiential appreciation uniquely predicts subjective judgements of MIL, even after accounting for the contribution of mattering, purpose and coherence to these types of evaluations. Overall, these findings support the hypothesis that valuing one's experiences is uniquely tied to perceptions of meaning. Implications for the incorporation of experiential appreciation as a fundamental antecedent of MIL are discussed.