Semiclassical Study Research Articles

Calculation of collisional line-broadening and shifting of acetylene using Complex Robert–Bonamy–Ma approach

A comprehensive semi-classical study of the collisional line broadening and shift coefficients of C2H2 by several key perturbers (H2, He, N2, C2H2, CO, and CO2) for astronomical applications using the Complex Robert–Bonamy–Ma (CRBM) framework is presented. Following the CRBM computational protocol, the intermolecular interaction potentials are constructed from atom-atom and electrostatic interactions, and then fitted to reproduce experimental room-temperature line-broadening parameters taken from the literature. In total, 657 experimental values are used in the fitting. The empirical potentials are then used to predict line broadening coefficients over a wide temperature range. Reference collisional line widths γ0 and temperature exponents n for the commonly used single-power law are produced, as well as a set of parameters for the double-power law, which better reproduces the temperature dependence of theoretical predictions. The vibrational dependence of the line widths is studied using a new ab initio isotropic polarizability surface of C2H2 and is found to be negligible. The computed line broadening parameters are found to agree well with the experimental data, while the modelling of line shits of HCCH is not satisfactory when compared to the experiment. The new line broadening data of C2H2 with the J (or m) dependence have been used to populate the ExoMol database www.exomol.com as part of the ExoMol pressure-broadening diet and can be used to model opacities of atmosphere of (extrasolar) planets. The CRBM methodology tested here on C2H2 can be used for other similar (closed-shell) systems in ExoMol that are important for exoplanetary atmospheric studies.

Effective Faraday interaction between light and nuclear spins of helium-3 in its ground state: a semiclassical study

Abstract We derive the semiclassical evolution equations for a system consisting of helium-3 atoms in the 2 3 S metastable state interacting with a light field far-detuned from the 2 3 S − 2 3 P transition, in the presence of metastability exchange collisions with ground state helium atoms and a static magnetic field. For two configurations, each corresponding to a particular choice of atom–light detuning in which the contribution of either the metastable level F = 1 / 2 or F = 3 / 2 is dominant, we derive a simple model of three coupled collective spins from which we can analytically extract an effective coupling constant between the collective nuclear spin and light. In these two configurations, we compare the predictions of our simplified model with the full model.

Semiclassical study of single-molecule magnets and their quantum phase transitions

We present a study on systems of single-molecule magnet systems using semiclassical analysis and catastrophe theory. Separatrices in the parameter space are constructed, which are useful for determining the structure of the Hamiltonian energy levels. In particular the Maxwell set separatrix determines the behaviour of the ground state of the system. We consider an external magnetic field with two components: one parallel to the easy magnetisation axis of the molecule and the other perpendicular to it. Using fidelity and heat capacity we were able to detect the signals of the quantum phase transitions as a function of the magnetic field components.

Empty space and the (positive) cosmological constant

I discuss empty space, as it appears in the physical foundations of relativistic field theories and in the semiclassical study of isolated systems. Of particular interest is the relationship between empirical measurements of the cosmological constant and the question of appropriate representation of empty space by spacetimes, or models of general relativity. Also considered is a speculative move that shows up in one corner of quantum gravity research. In pursuit of holographic quantum cosmology given a positive cosmological constant, there is evidently some freedom available for theoretical physicists to pick between two physically inequivalent spacetime representations of empty space, moving forward: de Sitter spacetime or its ‘elliptic’ cousin.

Charge Transfer and Electron Production in Proton Collisions with Uracil: A Classical and Semiclassical Study.

Cross sections for charge transfer and ionization in proton-uracil collisions are studied, for collision energies 0.05<E<2500 keV, using two computational models. At low energies, below 20 keV, the charge transfer total cross section is calculated employing a semiclassical close-coupling expansion in terms of the electronic functions of the supermolecule (H-uracil)+. At energies above 20 keV, a classical-trajectory Monte Carlo method is employed. The cross sections for charge transfer at low energies have not been previously reported and have high values of the order of 40 Å2, and, at the highest energies of the present calculation, they show good agreement with the previous results. The classical-trajectory Monte Carlo calculation provides a charge transfer and electron production cross section in reasonable agreement with the available experiments. The individual molecular orbital contributions to the total electron production and charge transfer cross sections are analyzed in terms of their energies; this permits the extension of the results to other molecular targets, provided the values of the corresponding orbital energies are known.

Semiclassical study of thermodynamic properties in the spontaneous fission of $$Cf^{252}$$

Semiclassical study of thermodynamic properties in the spontaneous fission of $$Cf^{252}$$

Quantum solvability of a nonlinear δ-type mass profile system: coupling constant quantization

In this paper, we discuss the quantum dynamics of a nonlinear system that admits temporally localized solutions at the classical level. We consider a general ordered position-dependent mass Hamiltonian in which the ordering parameters of the mass term are treated as arbitrary. The mass function here is singular at the origin. We observe that the quantum system admits bounded solutions but importantly the coupling parameter of the system gets quantized which has also been confirmed by the semiclassical study as well.

Semiclassical study of nonsequential triple ionization of Ar in strong laser fields

We study nonsequential triple ionization of Ar in strong laser fields using a classical trajectory Monte Carlo simulation. By tracing electrons' trajectories, we reveal the mechanisms of triple ionization, including multiple recollision and sequential ionization. One electron tunnels out and rescatters with its parent ion, either kicking off two electrons together or kicking off one of them and exciting another one, which will be freed by the laser field. Besides the above-dominated channels, the cascade rescattering for triple ionization is explored, in which the first tunneling electron rescatters with the parent ion ${\mathrm{Ar}}^{+}$ and kicks off the second electron and then the second electron gains energy in the laser field and rescatters with ${\mathrm{Ar}}^{2+}$, kicking off the third electron or boosting it to excited states to be freed later. Such a cascade channel connects three electrons step by step, and ${\mathrm{Ar}}^{3+}$ may have larger ultimate momenta compared to the triple ionization mediated by only one rescattering. Our simulation shows it is possible to control the cascade channel and extract it through the ion momentum distribution.

Semiclassical study of shape resonances in the Stark effect

Semiclassical behavior of Stark resonances is studied. The complex distortion outside a cone is introduced to study resonances in any energy region for the Stark Hamiltonians with non-globally analytic potentials. The non-trapping resolvent estimate is proved by the escape function method. The Weyl law and the resonance expansion of the propagator are proved in the shape resonance model. To prove the resonance expansion theorem, the functional pseudodifferential calculus in the Stark effect is established, which is also useful in the study of the spectral shift function.

Semiclassical study on photodetachment of hydrogen negative ion in a harmonic potential confined by a quantum well

Abstract We have studied the photodetachment dynamics of the H− ion in a harmonic potential confined in a quantum well for the first time. The closed orbits of the detached electron in a confined harmonic potential are found and the photodetachment spectra of this system are calculated. It is interesting to find that the photodetachment spectra depend sensitively on the size of the quantum well and the harmonic frequency. For smaller size of the quantum well, the harmonic potential can be considered as a perturbation, the interference effect between the returning electron wave bounced back by the quantum well and the initial outgoing wave is very strong, which makes the photodetachment spectra exhibits an irregular saw-tooth structure. With the increase of the size of the quantum well, the photodetachment spectra oscillates complicatedly in the higher energy region. For very large size of the quantum well, the photodetachment spectra approach to the case in a free harmonic potential, which is a regular saw-tooth structure. In addition, the harmonic frequency can also affect the photodetachment spectra of this system greatly. Our work provides a new method for the study of spatially confined low-dimensional systems and may guide the future experimental research for the photodetachment dynamics in the ion trap.

A semi-classical study on the Sauter-Schwinger effect of lepton antilepton pairs in vacuum

In this paper we purpose a fluctuation mechanism of the continuously appearing and disappearing lepton-antilepton pairs in vacuum. Within this approach, a semi-classical study on the Sauter-Schwinger effect is accomplished. We examined the suggested mechanism by comparing calculation of the Schwinger threshold our mechanism provides with the original one (m2c3/eℏ). While derivation we observed that the fluctuation mechanism suggests that muons and tauons should maintain the idea of classical lepton radius just as electrons maintain the idea of classical electron radius. The mechanism provides that lepton-antilepton pairs have initial total energies proportional to their rest mass energies with common constant of proportionality equal to1.47858037433852.

A classical and semiclassical study of collisions between Xq+ ions and water molecules.

Collisions of He2+, Li3+ and C3+ ions with water molecules are studied at energies ranging between 20 keV u-1 and 500 keV u-1. Three methods are employed: the classical trajectory Monte Carlo (CTMC), the expansion of the scattering wave function in terms of asymptotic frozen molecular orbitals (AFMO) and a lattice method to numerically solve the time-dependent Schrödinger equation (GridTDSE). Total cross sections for single ionization, single electron capture, transfer ionization and electron production are calculated and compared with previous close-coupling calculations and experiments. The fragmentation branching ratios are discussed.

Photon statistics of a double quantum dot micromaser: Quantum treatment

A semiconductor single-atom micromaser consists of a microwave cavity coupled to a gain medium, a double quantum dot driven out of equilibrium by a bias voltage. The masing threshold of this system was recently probed by measuring photon statistics in the cavity [Y-Y. Liu \textit{et al}, Phys. Rev. Lett. 119, 097702 (2017)]. In this paper, we develop an in-depth, rigorous understanding of this experiment and related works. First, we use a semiclassical theory and study transmission spectroscopy. This approach allows us to derive the masing threshold condition for arbitrary temperature and voltage bias, and expose microscopic principles required for realizing photon gain and thereby a photon amplifier. Next, by employing the quantum master equation approach we extend the Scully-Lamb quantum theory of a laser to the present setup, and investigate the statistics of emitted photons below and above the masing threshold as a function of experimentally tunable parameters. Although our focus is primarily on hybrid quantum dot circuit - quantum electrodynamics systems, our approach is adaptable to other light-matter systems where the gain medium consists of a mesoscopic structure.

Concentration of cylindrical Wigner measures

In this paper, we aim to characterize the cylindrical Wigner measures associated to regular quantum states in the Weyl C*-algebra of canonical commutation relations. In particular, we provide conditions at the quantum level sufficient to prove the concentration of all the corresponding cylindrical Wigner measures as Radon measures on suitable topological vector spaces. The analysis is motivated by variational and dynamical problems in the semiclassical study of bosonic quantum field theories.

Semiclassical transport properties of IrGa3: a promising thermoelectric material

IrGa3 is an intermetallic compound which is expected to be a metal, but a study on the electronic properties of this material to confirm its metallic character is not available in the literature. In this work, we report for the first time a first-principles density functional theory and semiclassical Boltzmann theory study of the structural, electronic and transport properties of this material. The inclusion of the spin–orbit coupling term is crucial to calculate accurately the electronic properties of this compound. We have established that IrGa3 is an indirect semiconductor with a narrow gap of 0.07 eV. From semiclassical Boltzmann transport theory, it is inferred that this material, with the appropriate hole concentration, could have a thermoelectric figure of merit at room temperature comparable to other intermetallic compounds such as FeGa3, though the transport properties of IrGa3 are highly anisotropic.

Semiclassics in a system without classical limit: The few-body spectrum of two interacting bosons in one dimension.

We present a semiclassical study of the spectrum of a few-body system consisting of two short-range interacting bosonic particles in one dimension, a particular case of a general class of integrable many-body systems where the energy spectrum is given by the solution of algebraic transcendental equations. By an exact mapping between δ-potentials and boundary conditions on the few-body wave functions, we are able to extend previous semiclassical results for single-particle systems with mixed boundary conditions to the two-body problem. The semiclassical approach allows us to derive explicit analytical results for the smooth part of the two-body density of states that are in excellent agreement with numerical calculations. It further enables us to include the effect of bound states in the attractive case. Remarkably, for the particular case of two particles in one dimension, the discrete energy levels obtained through a requantization condition of the smooth density of states are essentially in perfect agreement with the exact ones.

Conformation analysis and semiclassical dynamics study of charge exchange process induced by collision of C2+ ions with tetrahydrofuran

SynopsisWe present the results of recent investigations of charge transfer processes in the collisions of C2+ ions with heterocyclic molecules of tetrahydrofuran.

Dynamical cluster approximation plus semiclassical approximation study for a Mott insulator and d-wave pairing

Via a dynamical cluster approximation with N c = 4 in combination with a semiclassical approximation (DCA+SCA), we study the doped two-dimensional Hubbard model. We obtain a plaquette antiferromagnetic (AF) Mott insulator, a plaquette AF ordered metal, a pseudogap (or d-wave superconductor) and a paramagnetic metal by tuning the doping concentration. These features are similar to the behaviors observed in copper-oxide superconductors and are in qualitative agreement with the results calculated by the cluster dynamical mean field theory with the continuous-time quantum Monte Carlo (CDMFT+CTQMC) approach. The results of our DCA+SCA differ from those of the CDMFT+CTQMC approach in that the d-wave superconducting order parameters are shown even in the high doped region, unlike the results of the CDMFT+CTQMC approach. We think that the strong plaquette AF orderings in the dynamical cluster approximation (DCA) with N c = 4 suppress superconducting states with increasing doping up to strongly doped region, because frozen dynamical fluctuations in a semiclassical approximation (SCA) approach are unable to destroy those orderings. Our calculation with short-range spatial fluctuations is initial research, because the SCA can manage long-range spatial fluctuations in feasible computational times beyond the CDMFT+CTQMC tool. We believe that our future DCA+SCA calculations should supply information on the fully momentum-resolved physical properties, which could be compared with the results measured by angle-resolved photoemission spectroscopy experiments.

On-the-Fly ab Initio Semiclassical Calculation of Glycine Vibrational Spectrum.

We present an on-the-fly ab initio semiclassical study of vibrational energy levels of glycine, calculated by Fourier transform of the wavepacket correlation function. It is based on a multiple coherent states approach integrated with monodromy matrix regularization for chaotic dynamics. All four lowest-energy glycine conformers are investigated by means of single-trajectory semiclassical spectra obtained upon classical evolution of on-the-fly trajectories with harmonic zero-point energy. For the most stable conformer I, direct dynamics trajectories are also run for each vibrational mode with energy equal to the first harmonic excitation. An analysis of trajectories evolved up to 50 000 atomic time units demonstrates that, in this time span, conformers II and III can be considered as isolated species, while conformers I and IV show a pretty facile interconversion. Therefore, previous perturbative studies based on the assumption of isolated conformers are often reliable but might be not completely appropriate in the case of conformer IV and conformer I for which interconversion occurs promptly.

Modulational instability and localized modes in Heisenberg ferromagnetic chains with single-ion easy-axis anisotropy

A semiclassical theoretical study on the property of the modulational instability of corresponding linear spin-waves and the presence of nonlinear localized excitations in a discrete quantum ferromagnetic spin chain with single-ion easy-axis anisotropy is reported. We consider the Glauber coherent-state representation combined with the Dyson-Maleev transformation for local spin operators as the basic representation of the system, and derive the equation of motion by means of the Ehrenfest theorem. Using a modulational instability analysis of plane waves, we predict the existence regions of bright envelope solitons and intrinsic localized spin-wave modes. Besides, with the help of a semidiscrete multi-scale method, we obtain analytical solutions for the bright envelope soliton and intrinsic localized spin-wave mode. Moreover, we analyze their existence conditions, which agree with the results of modulational instability analysis.