Quantum Mechanical Theory Research Articles

Observations of the delayed-choice quantum eraser using coherent photons

Quantum superposition is the cornerstone of quantum mechanics, where interference fringes originate in the self-interference of a single photon via indistinguishable photon characteristics. Wheeler’s delayed-choice experiments have been extensively studied for the wave-particle duality over the last several decades to understand the complementarity theory of quantum mechanics. The heart of the delayed-choice quantum eraser is in the mutually exclusive quantum feature violating the cause-effect relation. Here, we experimentally demonstrate the quantum eraser using coherent photon pairs by the delayed choice of a polarizer placed out of the interferometer. Coherence solutions of the observed quantum eraser are derived from a typical Mach–Zehnder interferometer, where the violation of the cause-effect relation is due to selective measurements of basis choice.

Solvent Dynamics Are Critical to Understanding Carbon Dioxide Dissolution and Hydration in Water.

Simulations of carbon dioxide (CO2) in water may aid in understanding the impact of its accumulation in aquatic environments and help advance technologies for carbon capture and utilization (via, e.g., mineralization). Quantum mechanical (QM) simulations based on static molecular models with polarizable continuum solvation poorly reproduce the energetics of CO2 hydration to form carbonic acid in water, independent of the level of QM theory employed. Only with density-functional-theory-based molecular dynamics and rare-event sampling, followed by energy corrections based on embedded correlated wavefunction theory (in conjunction with density functional embedding theory), can a close agreement between theory and experiment be achieved. Such multilevel simulations can serve as benchmarks for simpler, less costly models, giving insight into potential errors of the latter. The strong influence of sampling/averaging over dynamical solvent configurations on the energetics stems from the difference in polarity of both the transition state and product (both polar) versus the reactant (nonpolar). When a solute undergoes a change in polarity during reaction, affecting its interaction with the solvent, careful assessment of the energetic contribution of the solvent response to this change is critical. We show that static models (without structural sampling) that incorporate three explicit water molecules can yield far superior results than models with more explicit water molecules because fewer water molecules yield less configurational artifacts. Static models intelligently incorporating both explicit (molecules directly participating in the reaction) and implicit solvation, along with a proper QM theory, e.g., CCSD(T) for closed-shell systems, can close the accuracy gap between static and dynamic models.

Quantum Time and Quantum Evolution

The problem of quantum time and evolution of quantum systems, where time is not a parameter, is considered. In our model, following some earlier works, time is represented by a quantum operator. In this paper, similarly to the position operators in the Schrödinger representation of quantum mechanics, this operator is a multiplication-type operator. It can be also represented by an appropriate positive operator-valued measure (POVM) which together with the 3D position operators/measures provide a quantum observable giving a position in the quantum spacetime. The quantum evolution itself is a stochastic process based on Lüder’s projection postulate. In fact, it is a generalization of the unitary evolution. This allows to treat time and generally the spacetime position as a quantum observable, in a consistent and observer-independent way.

Some halogenated anticancer agents, role of halide (-X) and their interaction mechanism with AT/GC base pairs: A computational study

Recently, a new class of halogen-based active anticancer agents have widely been developed which shows effective binding with AT/GC base pairs of DNA nucleobases. Usually intercalation, groove binding and covalent binding mechanisms are the most common drug-DNA binding pathways; but, the groove binding mechanism plays a crucial role in the stability of such drug-DNA complexes. As anticancer agent-DNA nucleobase interactions are very difficult to investigate by using common experimental techniques; therefore, theoretical methods may be quite helpful to analyze the proper mode of interaction for such drug-DNA systems. Past literature reveals that, quantum mechanical (QM) density functional theory (DFT) method is one of the best known tool for analyzing the different binding modes of halogenated anticancer agents with DNA nucleobases. Moreover, the halogen-bonding interaction in any biological system is fundamentally understood by investigating the mechanism of donor-acceptor complex formation between donor halogens and acceptor atoms within a receptor; such study is very competent for exploring the favoured anticancer agent-DNA interaction. In this current work, our main objective is to explore the effect of some intercalating and groove binding halogen-based anticancer agents with DNA nucleobase using computational method.

Charge trapping effect at the interface of ferroelectric/interlayer in the ferroelectric field effect transistor gate stack

We study the charge trapping phenomenon that restricts the endurance of n-type ferroelectric field-effect transistors (FeFETs) with metal/ferroelectric/interlayer/Si (MFIS) gate stack structure. In order to explore the physical mechanism of the endurance failure caused by the charge trapping effect, we first establish a model to simulate the electron trapping behavior in n-type Si FeFET. The model is based on the quantum mechanical electron tunneling theory. And then, we use the pulsed I d–V g method to measure the threshold voltage shift between the rising edges and falling edges of the FeFET. Our model fits the experimental data well. By fitting the model with the experimental data, we get the following conclusions. (i) During the positive operation pulse, electrons in the Si substrate are mainly trapped at the interface between the ferroelectric (FE) layer and interlayer (IL) of the FeFET gate stack by inelastic trap-assisted tunneling. (ii) Based on our model, we can get the number of electrons trapped into the gate stack during the positive operation pulse. (iii) The model can be used to evaluate trap parameters, which will help us to further understand the fatigue mechanism of FeFET.

Dynamics of System States in the Probability Representation of Quantum Mechanics.

A short description of the notion of states of quantum systems in terms of conventional probability distribution function is presented. The notion and the structure of entangled probability distributions are clarified. The evolution of even and odd Schrödinger cat states of the inverted oscillator is obtained in the center-of-mass tomographic probability description of the two-mode oscillator. Evolution equations describing the time dependence of probability distributions identified with quantum system states are discussed. The connection with the Schrödinger equation and the von Neumann equation is clarified.

THE PROBABILISTIC MODEL OF ULTRASHORT PULSES SCATTERING ON A FREE ELECTRON

We devoted our study to the generalization of the traditional approach for the description of photon scattering on free electrons in the case of ultrashort laser pulses (USLP). In the framework of the second order of quantum mechanical perturbation theory with the use of the Klein–Nishina formula, we derived the expression for the total scattering probability during the whole time of the pulse action that is applicable in the relativistic limit. The redshift of scattered pulse spectra at the scattering angle increase in the relativistic case was studied. The trends of the total scattering probability on the USLP duration were categorized.

Investigation on Adsorption of Polar Molecules in Vegetable Insulating Oil by Functional Fossil Graphene.

As a new engineering dielectric, vegetable insulating oil is widely used in electrical equipment. Small polar molecules such as alcohol and acid will be produced during the oil-immersed electrical equipment operation, which seriously affects the safety of equipment. The polar molecule can be removed by using functional fossil graphene materials. However, the structural design and group modification of graphene materials lack a theoretical basis. Therefore, in this paper, molecular dynamics (MD) and quantum mechanics theory (Dmol3) were utilized to study the adsorption kinetics and mechanism of graphene (GE), porous graphene (PGE), porous hydroxy graphene (HPGE), and porous graphene modified by hydroxyl and carboxyl groups (COOH-HPGE) on polar small molecules in vegetable oil. The results show that graphene-based materials can effectively adsorb polar small molecules in vegetable oil, and that the modification of graphene materials with carboxyl and hydroxyl groups improves their adsorption ability for polar small molecules, which is attributed to the conversion of physical adsorption to chemical adsorption by the modification of oxygen-containing groups. This study provides a theoretical basis for the design and preparation of graphene materials with high adsorption properties.

On the connection between perturbation theory and new semiclassical expansion in quantum mechanics

On the connection between perturbation theory and new semiclassical expansion in quantum mechanics

Construction and validation of the average molecular structure model of the bio-oil from solvent-thermal liquefaction of sawdust using molecular characterization and molecular simulation

Bio-oil is a potential renewable energy source that can be used as a green alternative to fossil crude oil, such as biofuel or asphalt additive. There are various processes for the preparation of bio-oil, but the lack of research on the molecular level of bio-oil has led to limitations in its application. Modeling the molecular structure of bio-oil would help to explore the relationship between the chemical composition of and its macroscopic properties and applications. In this context, the first average molecular model of sawdust bio-oil was developed by analyzing bio-oil structural characterization data, then the model was optimized and validated using quantum mechanics theory and molecular simulation. The results show that the sawdust bio-oil can be abstracted as an aromatic compound with the molecular formula C50H74O19, the simulated spectra are in good agreement with the experimental spectra and the model parameters such as energy, density and solubility parameters are in line with the actual conditions of the bio-oil, which proves the reasonableness of the model.

QUANTUM THEOLOGY AND “‘WE’ AND ‘THEY’”

QUANTUM THEOLOGY AND “‘WE’ AND ‘THEY’”

An exact imaginary-time path-integral phase-space formulation of multi-time correlation functions.

An exact representation of quantum mechanics using the language of phase-space variables provides a natural starting point to introduce and develop semiclassical approximations for the calculation of time correlation functions. Here, we introduce an exact path-integral formalism for calculations of multi-time quantum correlation functions as canonical averages over ring-polymer dynamics in imaginary time. The formulation provides a general formalism that exploits the symmetry of path integrals with respect to permutations in imaginary time, expressing correlations as products of imaginary-time-translation-invariant phase-space functions coupled through Poisson bracket operators. The method naturally recovers the classical limit of multi-time correlation functions and provides an interpretation of quantum dynamics in terms of "interfering trajectories" of the ring-polymer in phase space. The introduced phase-space formulation provides a rigorous framework for the future development of quantum dynamics methods that exploit the invariance of imaginary time path integrals to cyclic permutations.

Quantum Feedback at the Solid-Liquid Interface: Flow-Induced Electronic Current and Its Negative Contribution to Friction

A new quantum-mechanical theory predicts that a neutral liquid can generate an electric current in the solid wall along which it flows. The current in turn reduces the friction at the liquid-solid interface.

Moiré patterns and inversion boundaries in graphene/hexagonal boron nitride bilayers

In this paper a systematic examination of graphene/hexagonal boron nitride (g/hBN) bilayers is presented, through a recently developed two-dimensional phase field crystal model that incorporates out-of-plane deformations. The system parameters are determined by closely matching the stacking energies and heights of g/hBN bilayers to those obtained from existing quantum-mechanical density functional theory calculations. Out-of-plane deformations are shown to reduce the energies of inversion domain boundaries in hBN, and the coupling between graphene and hBN layers leads to a bilayer defect configuration consisting of an inversion boundary in hBN and a domain wall in graphene. Simulations of twisted bilayers reveal the structure, energy, and elastic properties of the corresponding moir\'e patterns and show a crossover as the misorientation angle between the layers increases from a well-defined hexagonal network of domain boundaries and junctions to smeared-out patterns. The transition occurs when the thickness of domain walls approaches the size of the moir\'e patterns and coincides with the peaks in the average von Mises and volumetric stresses of the bilayer.

Molecular Docking of the Inhibitory Activities of Selected Phytochemicals in Artemisia Afra Against NADH-Ubiquinone Oxidoreductase of Plasmodium Falciparum (PfNDH2)

Nicotinamide Adenine Dinucleotide Hydrogen (NADH)-ubiquinone oxidoreductase in Plasmodium falciparum (PfNDH2) constitute a feasible target for anti-malarial drug discovery. This work aims at investigating the inhibitory activities of selected phytochemicals in Artemisia Afra against NADH-Ubiquinone Oxidoreductase of Plasmodium Falciparum. 50 phytochemicals were selected based on structural stability. Quantum mechanical Density Functional Theory (DFT) studies with B3LYP at 6-311G* level was done on pfNDH2 as the apoprotein control. Pharmacokinetic ADMET profiling, bioactivity assessment, physicochemical studies, molecular docking was used to study the PfNDH2 inhibiting activities of the 50 compounds from Artemisia afra. Out of these 50 phytochemicals, 2,4,6-Triphenyl-1,3 dioxane (2,4,6 TPD), chamazulene, aromadendrene, 1-epi-bBicyclosesquiphellandrene (1-EBSP) and cis-muurola-3,5-diene (CM3,5D) passed the physicochemical properties of the Lipinski rule of 5, binding mode, molecular interaction and ADMET calculations. These five compounds also showed high binding affinity of -8.9 kJ/mol, -7.7kJ/mol, -7.3kJ/mol, -7.1kJ/mol and -7.1kJ/mol at the binding pores of PfNDH2 respectively. The reactivity of these compounds was also investigated by the electron donating and accepting activities of the compounds using Density Functional Theory calculated Higher Occupied Molecular Orbital, Lower Unoccupied Molecular Orbital energy and HOMO/LUMO energy gap revealed the stability of the compounds due to the low energy gap values obtained. The values obtained showed that aromadendrene and chamazulene were potential inhibitors of PfNDH2 and were the most potent and therefore, recommended for therapeutic efficacy investigation.

D4-branes wrapped on four-dimensional orbifolds through consistent truncation

We construct a consistent truncation of six-dimensional matter coupled F(4) gauged supergravity on a cornucopia of two-dimensional surfaces including a spindle, disc, domain wall and other novel backgrounds to four-dimensional minimal gauged supergravity. Using our consistent truncation we uplift known AdS2× Σ1 solutions giving rise to four-dimensional orbifold solutions, AdS2× Σ1 ⋉ Σ2. We further uplift our solutions to massive type IIA supergravity by constructing the full uplift formulae for six-dimensional U(1)2-gauged supergravity including all fields and arbitrary Romans mass and gauge coupling. The solutions we construct are naturally interpreted as the near-horizon geometries of asymptotically AdS6 black holes with a four-dimensional orbifold horizon. Alternatively, one may view them as the holographic duals of superconformal quantum mechanical theories constructed by compactifying five-dimensional USp(2N) theory living on a stack of D4-D8 branes on the four-dimensional orbifolds. As a first step to identifying these quantum mechanical theories we compute the Bekenstein-Hawking entropy holographically.

CHARMM-GUI QM/MM interfacer for the hybrid QM/MM molecular dynamics simulations.

Molecular mechanical (MM) force fields are constructed based on the empirical potentials, describing intramolecular and intermolecular potentials. Molecular dynamics (MD) simulation utilizing MM force fields is a robust tool to investigate large biomolecular systems, but the changes in electronic structures during a chemical process are overlooked in classical mechanics. Quantum mechanical (QM) treatments are needed for such changes including bond forming/breaking and charge transfers, but a high computational cost limits its usages with up to hundreds of atoms or less. A hybrid QM/MM approach, where the reactive part of the system is treated with QM and the remainder by cheap MM potentials, can effectively capture the reaction without significantly increasing the computational cost. For the different nature of the QM versus MM theories, however, the setup of biomolecular QM/MM simulation is known to be time consuming even to QM/MM experts. We present CHARMM-GUI QM/MM Interfacer that prepares QM/MM simulations with a user-selected QM region and various QM theories in multiple simulation packages. A non-trivial and error-prone QM/MM simulation setup involving link-atom insertion and charge distribution can be seamlessly prepared in QM/MM Interfacer. A few representative systems are simulated to delineate the robustness of QM/MM Interfacer. We hope both QM/MM beginners and experts to find the module's quick and accurate QM/MM simulation setup useful for their important applications.

“A call to action”: Schrödinger's representation of quantum mechanics via Hamilton's principle

A few years ago, one of the former Editors of this journal launched “a call to action” (E. F. Taylor, Am. J. Phys. 71, 423–425 (2003)) for a revision of teaching methods in physics in order to emphasize the importance of the principle of least action. In response, we suggest the use of Hamilton's principle of stationary action to introduce the Schrödinger equation. When considering the geometric interpretation of the Hamilton–Jacobi theory, the real part of the action S defines the phase of the wave function exp iS/ℏ, and requiring the Hamilton–Jacobi wave function to obey wave-front propagation (i.e., Re(S) is a constant of the motion) yields the Schrödinger equation.

Fusion enhancement within a collective clusterization approach applied to the isotopic chain of neutron-rich light-mass compound nuclei

The dynamics of neutron-rich light-mass compound nuclei $^{24,25,26,27}\mathrm{Mg}^{*}$ formed in $^{12,13,14,15}\mathrm{C}+^{12}\mathrm{C}$ fusion reactions, respectively, is explored at different ${E}_{\mathrm{c}.\mathrm{m}.}$ values within the dynamical cluster decay model (DCM). DCM is based on the quantum mechanical fragmentation theory, which treats the binary fragmentation of emitting compound nucleus as light particles (LPs), intermediate mass fragments (IMFs), as well as symmetric mass fragments (SMFs), on equal footing, which is not the case with other fission and statistical models. All calculations are made for spherical considerations and angular momenta taken up to the $\ensuremath{\ell}$-critical value for the respective reactions. A fusion enhancement is observed as we go from compound nuclei (CN) having an even number of neutrons ($^{24,26}\mathrm{Mg}^{*}$) to CN with the odd number of neutrons ($^{25,27}\mathrm{Mg}^{*}$). Interestingly, we find that the only parameter of the DCM, the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$ related to the barrier lowering, is in linear relation with ${\ensuremath{\sigma}}_{\mathrm{Fusion}}$ at chosen incident laboratory energy. The fusion enhancement is found to be larger for odd neutron number nuclei, which indicates the influence of unpaired neutrons on fusion cross sections. Within the formalism of DCM, the phenomenon of fusion enhancement finds its base in the process of collective clusterization, which is quite evident from the larger values of summed-up preformation probability for the reactions having odd mass projectiles or forming odd mass CN. The DCM calculated fusion cross sections are in good agreement with the available experimental data for the given reactions.

Quantum Oscillator at Temperature T and the Evolution of a Charged-Particle State in the Electric Field in the Probability Representation of Quantum Mechanics

A short review constructing the probability representation of quantum mechanics is given, and examples of the probability distributions describing the states of quantum oscillator at temperature T and the evolution of quantum states of a charged particle moving in the electric field of an electrical capacitor are considered. Explicit forms of time-dependent integrals of motion, linear in the position and momentum, are used to obtain varying probability distributions describing the evolving states of the charged particle. Entropies corresponding to the probability distributions of initial coherent states of the charged particle are discussed. The relation of the Feynman path integral to the probability representation of quantum mechanics is established.