Interaction Hamiltonian Research Articles

Decoherence and Landauer’s principle in qubit-cavity quantum-field-theory interaction

We consider quantum decoherence and Landauer’s principle in qubit-cavity quantum field theory (QFT) interaction, treating the qubit as the system and cavity QFT as the environment. In particular, we investigate the changes that occur in the system with a pure initial state and environment during the decoherence process, with or without energy dissipation, and compare the results with the case in which the initial state of the system is a mixed state and thus decoherence is absent. When we choose an interaction Hamiltonian such that the energy and coherence of the system change simultaneously, the population change of the system and the energy change are the same when the initial state is mixed. However, the decoherence terms increase the von Neumann entropy of the system. In this case the energy change and decoherence of the system are not independent physical processes. The decoherence process maintains unitarity. On the other hand, if the interaction Hamiltonian does not change the energy of the system, there is only the decoherence effect. The environment will be a distribution in the basis of the displaced number state and always increases the energy. Landauer’s principle is satisfied in both cases.

Free energy landscape of wrapping of lipid nanocluster by polysaccharides

Wrapping of a 20-mer cholesterol nano-cluster (CHL-nanoC) by two widely different types of β-glucan polysaccharides (23–25 mers) having significantly varying glycosidic linkage patterns and side chains is studied by Well-Tempered MetaDynamics (WT-MetaD) simulations. The problem has its relevance in the faecal sterol and bile acid excretion in humans and the role of dietary fibres in aiding the process and combating dyslipidemia. Additionally, the distinctive collective variables studied here can be extended for modeling of polymer wrapped soft clusters/nano-particles in general. The wrapping ability is observed to be significantly correlated to the bending of the polysaccharide chain, an attribute of the glycosidic linkage type. By biasing two unique collective variables, the radius of gyration of the polysaccharide (Rg, poly) and the second order Legendre polynomial of the segment orientation parameter, θ, we could successfully observe the wrapping process. This work compares in detail the physical properties of the polysaccharide encapsulated CHL-nanoC by probing the radius of curvature (Rcurv, poly) of the polysaccharides, their coordination number with respect to the CHL-nanoC (CN), fractional CHL-nanoC surface coverage and the electrostatic surface potentials of the complex assembly. Results indicate that the β-glucan having 1–4 glycosidic linked monomers with intermittent 1–3 linkage is able to wrap the CHL-nanoC more effectively. The 1–3 glycosidic linked β-glucan with 1–6 glycosidic bonds in side chains is significantly curled up and appears to be less efficient in wrapping the nanoC. This work provides a comparative molecular level picture of mutual interaction between two major dietary polysaccharide variants and lipid globules as indicated by numerous clinical level studies involving mice and human models.

Spatial Tightness at the Edge of Gibbsian Line Ensembles

Consider a sequence of Gibbsian line ensembles, whose lowest labeled curves (i.e., the edge) have tight one-point marginals. Then, given certain technical assumptions on the nature of the Gibbs property and underlying random walk measure, we prove that the entire spatial process of the edge is tight. We then apply this black-box theory to the log-gamma polymer Gibbsian line ensemble, which we construct. The edge of this line ensemble is the transversal free energy process for the polymer, and our theorem implies tightness with the ubiquitous KPZ class 2/3 exponent, as well as Brownian absolute continuity of all the subsequential limits. A key technical innovation which fuels our general result is the construction of a continuous grand monotone coupling of Gibbsian line ensembles with respect to their boundary data (entrance and exit values, and bounding curves). Continuous means that the Gibbs measure varies continuously with respect to varying the boundary data, grand means that all uncountably many boundary data measures are coupled to the same probability space, and monotone means that raising the values of the boundary data likewise raises the associated measure. This result applies to a general class of Gibbsian line ensembles where the underlying random walk measure is discrete time, continuous valued and log-convex, and the interaction Hamiltonian is nearest neighbor and convex.

Interactions of quantum systems with pulses of quantized radiation: From a cascaded master equation to a traveling mode perspective

The interaction of a propagating pulse of quantum radiation with a localized quantum system can be described by a cascaded master equation with a distinct initially populated input and a finally populated output field mode [Kiilerich and M\o{}lmer, Phys. Rev. Lett. 123, 123604 (2019)]. By transformation to an appropriate interaction picture, we break the cascaded nature of the master equation and recover an effective time-dependent interaction with a lossless single mode and a supplementary lossy mode. The former closely represents the traveling pulse, while the latter constitutes a non-Markovian component in the exchange of quanta between the scatterer and the quantized field. The transformed master equation offers important insights into the system dynamics, and it permits numerically efficient solutions.

Revisiting the electronic structure of N2-bound cAAC-borylene at the CASSCF level: a detailed bonding picture of borylene-N2 interaction.

A base-trapped borylene species featuring a cyclic-(alkyl)(amino)carbene (cAAC) has shown unique bonding interactions with dinitrogen, thereby, opening a new avenue for N2 activation by main-group compounds. The detailed electronic structure and qualitative bonding picture between cAAC-trapped borylene and N2 remain to be fully understood. This work presents a multiconfigurational complete active space self-consistent field (CASSCF)-based electronic structure investigation on the N2-bound cAAC-borylene species (1) isolated by Braunschweig et al. Specifically, the synergistic bonding between the borylene units and N2 involving the donation from the N-N σ to the unoccupied orbital of borylene and back-donation from the occupied orbital of borylene to the N-N π* has been unequivocally established using CASSCF-derived natural orbitals and electronic configuration. Bonding interactions between the HOMO of the borylene units and the N-N π* (HOMOcAAC-B + π*NN) and the LUMO of the borylene units and the N-N σ (LUMOcAAC-B + σNN) in 1 were apparent through the CASSCF-derived natural orbitals. The unique bonding of the B-N-N-B core in 1 and the resulting geometry have also been compared with the M-N-N-M core of a prototypical transition metal(M)-N2 complex. Finally, the change in the electronic structure and geometry of the N2-bound borylene species 1 on two-electron reduction has been investigated in the context of N2 activation.

Surface hopping simulations on charge separation in an organic donor-acceptor system.

Charge separation in organic solar cells is a long-lasting and heavily debated issue. Here, we use the surface hopping method based on the Pariser-Parr-Pople (PPP) Hamiltonian and configuration interaction singles (CIS) approximation to simulate the charge separation process in an organic donor-acceptor system. The system is composed of one donor polymer chain and four acceptor polymer chains, and they are all stacked face-to-face. We let the system to relax from a photoexcited state, and then we observed that the electron is transferred from the donor chain to different acceptor chains and the hole is left on the donor chain, forming polaron pairs with different electron-hole distances. By performing statistical analysis on a number of trajectories, we found that the electron and the hole are fully separated before the system relaxes to its lowest excited state. The yield of free charges shows a significant dependence on the donor-acceptor band offset which provides the driving force for charge separation, while showing negligible dependence on the photoexcitation energy. The external electric field has a remarkable effect on the yield of free charges.

MetaFunc: taxonomic and functional analyses of high throughput sequencing for microbiomes.

The identification of functional processes taking place in microbiome communities augment traditional microbiome taxonomic studies, giving a more complete picture of interactions taking place within the community. While there are applications that perform functional annotation on metagenomes or metatranscriptomes, very few of these are able to link taxonomic identity to function or are limited by their input types or databases used. Here we present MetaFunc, a workflow which takes RNA sequences as input reads, and from these (1) identifies species present in the microbiome sample and (2) provides gene ontology annotations associated with the species identified. In addition, MetaFunc allows for host gene analysis, mapping the reads to a host genome, and separating these reads, prior to microbiome analyses. Differential abundance analysis for microbe taxonomies, and differential gene expression analysis and gene set enrichment analysis may then be carried out through the pipeline. A final correlation analysis between microbial species and host genes can also be performed. Finally, MetaFunc builds an R shiny application that allows users to view and interact with the microbiome results. In this paper, we showed how MetaFunc can be applied to metatranscriptomic datasets of colorectal cancer.

Culture and industry of the Acheulean Age

The readers of Herald of the Russian Academy of Sciences are presented with reflections on volumes III and IV of the fundamental multivolume summarizing work on the Paleolithic by the outstanding archaeologist and historian Academician A.P. Derevyanko. The main stages in the development of humankind and its technology, known from preserved ancient sites, are described. The finds at the sites consist mostly of remains of the stone industry and crushed bones of animals hunted by ancient humans. A great piece of luck is the discovery of the remains of humans. Volumes III and IV of Derevyanko’s book are devoted to the Acheulean age, a period marked by the beginning of complex interactions between representatives of the first and second waves of migrants from Africa: Homo erectus with the Oldowan tradition of stone processing and Homo Heidelbergensis of the second wave of migrants, who possessed the world’s first universal tool of a standard almond shape, i.e., the hand axe. Following the pattern of the distribution of the Heidelberg man and the hand axe, the author of this article comes to the conclusion that volumes III and IV of Derevyanko’s book clearly reflect the complex picture of interactions between the carriers of the two different technological cultures. The Acheulean age sees, for the first time in history, the formation of local cultural provinces of primitive human communities coming from different origins, which raises, also for the first time, the issue of interactions between different races and cultural traditions.

Параллельная многокубитная эволюция в протоколе квантового неразрушающего взаимодействия

To date, two-qubit quantum logic gates have become an essential part of quantum computing. The study of methods for their implementation is an important practical problem for various quantum optical and information applications. In this paper, we have considered a protocol for multimode quantum non demolition interaction between an atomic ensemble and multimode light with orbital angular momentum in order to analyze the applicability of this protocol in discrete variables computing. We have developed a multimode interaction Hamiltonian and analyzed the dynamics of field and atomic variables depending on the structure of the driving field. We discuss in detail the procedure for separating qubit noninteracting subsystems on a set of atomic and field modes for various values of the orbital angular momentum of the driving field. Such a procedure helps to reduce the considered protocol to the parallel evolution of two-qubit closed systems.

Learning statistics with interactive pictures using R Shiny: Generally preferred, but not generally advantageous

AbstractConstructing interactive web apps has become more accessible for instructors, for example, by using the R package Shiny. Here we explored learners' preferences and the efficiency of interactive simulations versus static pictures in acquiring statistics knowledge of Cohen's d and standard normal distribution. Results revealed that students' spontaneous interaction with pictures was infrequent (pilot study, N = 26). While prompts (Exp. 1, N = 152) effectively ensured the manipulation of simulations, student exposure to interactive simulations led to longer learning times though similar test performance compared with student exposure to static pictures. Multiple interactive representations led to lower test performance than single interactive and static representations (Exp. 2, N = 117). Though no advantage was gained regarding learning outcomes, participants preferred the interactive variant (Exp. 3, N = 119). Taken together, this study demonstrates that the superiority of interactive pictures cannot be assumed to hold in general. Further work should evaluate how mental model construction can be effectively scaffolded by interactive simulations.

Attentional bias towards social interactions during viewing of naturalistic scenes.

Human visual attention is readily captured by the social information in scenes. Multiple studies have shown that social areas of interest (AOIs) such as faces and bodies attract more attention than non-social AOIs (e.g., objects or background). However, whether this attentional bias is moderated by the presence (or absence) of a social interaction remains unclear. Here, the gaze of 70 young adults was tracked during the free viewing of 60 naturalistic scenes. All photographs depicted two people, who were either interacting or not. Analyses of dwell time revealed that more attention was spent on human than background AOIs in the interactive pictures. In non-interactive pictures, however, dwell time did not differ between AOI type. In the time-to-first-fixation analysis, humans always captured attention before other elements of the scene, although this difference was slightly larger in interactive than non-interactive scenes. These findings confirm the existence of a bias towards social information in attentional capture and suggest our attention values social interactions beyond the presence of two people.

On the breakdown of the perturbative interaction picture in Big Crunch/Big Bang or the true reason why perturbative string amplitudes on temporal orbifolds diverge

We discuss how the perturbative particle paradigm fails in certain background with space-like singularity but asymptotically flat which should admit a S-matrix. The Feynman approach relies on the interaction picture. This approach means that we can interpret interactions as exchanges of particles. Particles are the modes of the quadratic part of the Lagrangian. In certain backgrounds with space-like singularity the interaction Hamiltonian is well defined but the perturbative expansion of the evolution operator through the singularity and the perturbative S matrix do not exist. On the other hand, relying on minisuperspace approximation we argue that the non perturbative evolution operator does exist. The complete breakdown of the perturbative expansion explains why the perturbative computations in the covariant formalism in string theory in temporal orbifold fail, at least at the tree level.

Effects of dung beetle activity on tropical forest plants

Dung beetles are recognized as providers of important ecosystem functions, most of which are derived from the removal of vertebrate dung from the soil surface. These insects occur in nearly all terrestrial biomes but are most diverse in the humid tropics. Several of the ecological functions attributed to dung beetles are related to their direct and indirect interactions with plants. Among these functions, the secondary dispersal of seeds defecated by mammals has received the most attention in tropical forests. Nonetheless, while several aspects of secondary seed dispersal by dung beetles are relatively well understood, others remain understudied or have not been addressed at all. Thus, a broad generalization about the effects of secondary seed dispersal by dung beetles on plant fitness remains somewhat elusive. Furthermore, other effects of dung beetle activity on tropical plants have received very little attention. A few studies have shown that through their behaviors of dung burial and soil-excavation, dung beetles can shape seed bank structure and dynamics. Also, though numerous greenhouse studies and field experiments in agricultural lands and temperate grasslands have shown that dung beetle activity increases plant nutrient uptake and yield, it is uncertain whether such effects are common in tropical forests. Here, we review and synthesize our current knowledge on how dung beetles affect tropical forest plants by dispersing defecated seeds, shaping the structure and dynamics of seed banks, and influencing the performance of understory seedlings. We focus on the Neotropics, where most studies on the effects of dung beetles on tropical forest plants have been carried out, but we also show results from other regions and biomes, to present a more general picture of these beetle-plant interactions. Throughout the review we emphasize aspects that need more research to allow generalizations and point out those questions that remain unanswered. We hope that this review will stimulate more research about the fascinating interactions between dung beetles and plants in tropical ecosystems.

Mid Infrared supercontinuum generation in a silicon germanium photonic waveguide

We report simulations of pulse evolution along a 5 cm long silicon germanium (SiGe) photonic waveguide. Femtosecond laser pulses of duration 210 fs and wavelength of 4.7 µm close to the first zero dispersion wavelength (ZDW) of SiGe situated at 4.6 µm were used in pumping the SiGe photonic waveguide. Simulations were made by solving the generalised nonlinear Schrödinger equation for the femtosecond pump pulse evolution along the length of SiGe photonic waveguide using the fourth order Runge-Kutta in the interaction picture method. The simulated supercontinum spans the 2.5–8.5 µm spectral region comprising of molecular signatures for most hazardous and greenhouse gases making it attractive for environmental monitoring applications.

Characterization of H-Brownian Gibbsian line ensembles

In this paper we show that an $H$-Brownian Gibbsian line ensemble is completely characterized by the finite-dimensional marginals of its lowest indexed curve for a large class of interaction Hamiltonians $H$. A particular consequence of our result is that the KPZ line ensemble is the unique line ensemble that satisfies the $H_1$-Brownian Gibbs property with $H_1(x) = e^x$ and whose lowest indexed curve is equal to the Hopf-Cole solution to the narrow wedge KPZ equation.

Scattering of low energy neutrinos and antineutrinos by neon and argon

The theory of scattering of low energy neutrinos and antineutrinos by atomic electrons has recently been developed [ I. B. Whittingham, Phys. Rev. D 105, 013008 (2022)] using the bound interaction picture in configuration space to fully implement the relationship between the neutrino helicities and the orbital and spin angular momenta of the atomic electrons. The energy spectra of ionization electrons produced by scattering of neutrinos and antineutrinos with energies of 5, 10, 20, and 30 keV by hydrogen, helium and neon were calculated using Dirac screened Coulombic eigenfunctions. This paper reports further applications of this theory, to a new calculation of the energy spectra for neon, as the original calculation used some screening constants which underestimated the effects of screening in the inner subshells, and to scattering by argon. The results are presented as ratios to the corresponding quantities for scattering by $Z$ free electrons. The new spectra ratios for neon are larger than the original ratios by $\ensuremath{\approx}0.03$--$\ensuremath{\approx}0.14$, with the greatest increases occurring for 10 keV neutrinos and antineutrinos. Integrated spectra ratios range from 0.16 to 0.59 for neon, and from 0.15 to 0.48 for argon, as the neutrino energy increases from 5 to 30 keV.

Crosstalk Suppression in Individually Addressed Two-Qubit Gates in a Trapped-Ion Quantum Computer.

Crosstalk between target and neighboring spectator qubits due to spillover of control signals represents a major error source limiting the fidelity of two-qubit entangling gates in quantum computers. We show that in our laser-driven trapped-ion system coherent crosstalk error can be modeled as residual Xσ[over ^]_{ϕ} interaction and can be actively canceled by single-qubit echoing pulses. We propose and demonstrate a crosstalk suppression scheme that eliminates all first-order crosstalk utilizing only local control of target qubits, as opposed to an existing scheme which requires control over all neighboring qubits. We report a two-qubit Bell state fidelity of 99.52(6)% with the echoing pulses applied after collective gates and 99.37(5)% with the echoing pulses applied to each gate in a five-ion chain. This scheme is widely applicable to other platforms with analogous interaction Hamiltonians.

Michel parameters in the presence of massive Dirac and Majorana neutrinos

We analyse the effects of Dirac and Majorana neutrinos on leptonic decays of muon and tau leptons using the most general four-lepton effective interaction Hamiltonian of dimension six. We calculate the specific energy and angular distribution of the final charged lepton, including the polarizations of the initial and final charged leptons. We discuss the new generalized Michel parameters and focus on the effects of the heavy neutrino masses that would lead to sizable contributions on scenarios where the new sterile neutrinos have non-negligible mixing. Specifically, the most promising scenario is found for the case of τ decay with one heavy final-state neutrino with a mass around 102 − 103 MeV, where the linear term suppression could be of order 10−4, low enough to be measured in current and forthcoming experiments.

Relaxation Dynamics in a Long-Range System with Mixed Hamiltonian and Non-Hamiltonian Interactions

Sometimes the dynamics of a physical system is described by non-Hamiltonian equations of motion, and additionally, the system is characterized by long-range interactions. A concrete example is that of particles interacting with light as encountered in free-electron laser and cold-atom experiments. In this work, we study the relaxation dynamics to non-Hamiltonian systems, more precisely, to systems with interactions of both Hamiltonian and non-Hamiltonian origin. Our model consists of $N$ globally-coupled particles moving on a circle of unit radius; the model is one-dimensional. We show that in the infinite-size limit, the dynamics, similarly to the Hamiltonian case, is described by the Vlasov equation. In the Hamiltonian case, the system eventually reaches an equilibrium state, even though one has to wait for a long time diverging with $N$ for this to happen. By contrast, in the non-Hamiltonian case, there is no equilibrium state that the system is expected to reach eventually. We characterize this state with its average magnetization. We find that the relaxation dynamics depends strongly on the relative weight of the Hamiltonian and non-Hamiltonian contributions to the interaction. When the non-Hamiltonian part is predominant, the magnetization attains a vanishing value, suggesting that the system does not sustain states with constant magnetization, either stationary or rotating. On the other hand, when the Hamiltonian part is predominant, the magnetization presents long-lived strong oscillations, for which we provide a heuristic explanation. Furthermore, we find that the finite-size corrections are much more pronounced than those in the Hamiltonian case; we justify this by showing that the Lenard-Balescu equation, which gives leading-order corrections to the Vlasov equation, does not vanish, contrary to what occurs in one-dimensional Hamiltonian long-range systems.

Geometric-arithmetic master equation in large and fast open quantum systems

Understanding nonsecular dynamics in open quantum systems is addressed here, with emphasis on systems with large numbers of Bohr frequencies, zero temperature, and fast driving. We employ the master equation, which replaces arithmetic averages of the decay rates in the open system, with their geometric averages, and find that it can improve the second order perturbation theory, known as the Redfield equation, while enforcing complete positivity on quantum dynamics. The characteristic frequency scale that governs the approximation is the minimax frequency: the minimum of the maximum system oscillation frequency and the bath relaxation rate; this needs to be larger than the dissipation rate for it to be valid. The concepts are illustrated on the Heisenberg ferromagnetic spin-chain model. To study the accuracy of the approximation, a Hamiltonian is drawn from the Gaussian unitary ensemble, for which we calculate the fourth order time-convolutionless master equation, in the Ohmic bath at zero temperature. Enforcing the geometric average, decreases the trace distance to the exact solution. Dynamical decoupling of a qubit is examined by applying the Redfield and the geometric-arithmetic master equations, in the interaction picture of the time dependent system Hamiltonian, and the results are compared to the exact path integral solution. The geometric-arithmetic approach is significantly simpler and can be super-exponentially faster compared to the Redfield approach.