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To simulate solar Coronal Mass Ejections (CMEs), predict their time of arrival and geomagnetic impact, it is important to accurately model the background solar wind conditions in which CMEs propaga...

Ab initio molecular dynamics (AIMD) is a powerful tool to predict properties of molecular and condensed matter systems. However, the quality of this procedure relies on the availability of rigorous electronic structure calculations. The development of quantum processors has shown great potential for the efficient evaluation of accurate ground and excited state energies of molecular systems, opening up new avenues for molecular dynamics simulations. In this work, we address the use of variational quantum algorithms for the calculation of accurate atomic forces to be used in AIMD. In particular, we provide solutions for the alleviation of the statistical noise associated with the measurements of the expectation values of energies and forces, as well as schemes for the mitigation of the hardware noise sources (in particular, gate infidelities, qubit decoherence, and readout errors). Despite the relative large error in the calculation of the potential energy, our results show that the proposed algorithms can provide accurate MD trajectories in the microcanonical (constant energy) ensemble. Furthermore, exploiting the intrinsic noise associated to the quantum measurement process, we also propose a Langevin dynamics algorithm for the simulation of canonical, i.e., constant temperature, dynamics. Both algorithms (microcanonical and canonical) are applied to the simulation of simple molecular systems such as H2 and H3+. Finally, we also provide results for the dynamics of H2 obtained with IBM quantum computer ibmq_athens.

In this paper, we investigate the transient response of Lorentz force at finite magnetic Reynolds numbers $ {R_{m}}$ on an electrically conducting rectangular bar that is strongly accelerated in the presence of a localized magnetic field. This is done through numerical simulations utilizing a coupled finite-difference boundary element approach. The results show good qualitative agreement with existing experiments with a circular cylinder. The Lorentz force rise time is seen to be a linear function of $ {R_{m}}$ . The linear dependence of Lorentz force on $ {R_{m}}$ is found to be valid only for low values of $ {R_{m}}$ , after which the slope decays leading to an apparent saturation in the Lorentz force at sufficiently large values of $ {R_{m}}$ . Our results provide important information for the development of Lorentz force flow meters for transient flow applications.

The Coupled Cluster (CC) method is used to compute the electronic correlation energy in atoms and molecules and often leads to highly accurate results. However, due to its single-reference nature, standard CC in its projected form fails to describe quantum states characterized by strong electronic correlations and multi-reference projective methods become necessary. On the other hand, quantum algorithms for the solution of many-electron problems have also emerged recently. The quantum unitary variant of CC (UCC) with singles and doubles (q-UCCSD) is a popular wavefunction Ansatz for the variational quantum eigensolver algorithm. The variational nature of this approach can lead to significant advantages compared to its classical equivalent in the projected form, in particular, for the description of strong electronic correlation. However, due to the large number of gate operations required in q-UCCSD, approximations need to be introduced in order to make this approach implementable in a state-of-the-art quantum computer. In this work, we evaluate several variants of the standard q-UCCSD Ansatz in which only a subset of excitations is included. In particular, we investigate the singlet and pair q-UCCD approaches combined with orbital optimization. We show that these approaches can capture the dissociation/distortion profiles of challenging systems, such as H4, H2O, and N2 molecules, as well as the one-dimensional periodic Fermi-Hubbard chain. These results promote the future use of q-UCC methods for the solution of challenging electronic structure problems in quantum chemistry.

In this work we investigate methods to improve the efficiency and scalability of quantum algorithms for quantum chemistry applications. We propose a transformation of the electronic structure Hamiltonian in the second quantization framework into the particle-hole picture, which offers a better starting point for the expansion of the system wave function. The state of the molecular system at study is parametrized so as to constrain the sampling of the corresponding wave function within the sector of the molecular Fock space that contains the desired solution. To this end, we explore different mapping schemes to encode the molecular ground state wave function in a quantum register. Taking advantage of known post-Hartree-Fock quantum chemistry approaches and heuristic Hilbert space search quantum algorithms, we propose a new family of quantum circuits based on exchange-type gates that enable accurate calculations while keeping the gate count (i.e., the circuit depth) low. The particle-hole implementation of the unitary coupled-cluster (UCC) method within the variational quantum eigensolver approach gives rise to an efficient quantum algorithm, named q-UCC, with important advantages compared to the straightforward translation of the classical coupled-cluster counterpart. In particular, we show how a single Trotter step in the expansion of the system wave function can accurately and efficiently reproduce the ground-state energy of simple molecular systems.

While he derived the equation for the radiation force, Dirac (1938) mentioned a possibility to use different choices for the 4-momentum of an emitting electron. Particularly, the 4-momentum could be non-colinear to the electron 4-velocity. This ambiguity in the electron 4-momentum allows us to assume that the mass of emitting electron may be an operator, or, at least, a 4-tensor instead of being the usually assumed scalar, which relates the 4-velocity of a bare charge to the total momentum of a dressed point electron, the latter being a total of the momentum of the bare electron and that of the own electromagnetic field. On applying the re-normalization procedure to the mass operator, we arrive at an interesting dichotomy. The first choice (more close to traditional one) ensures the radiation force to be orthogonal to the 4-velocity. In this way the re-normalization results in the Lorentz-Abraham-Dirac equation or in the Eliezer equation. However, the 4-momentum of electron in this case is not well defined: the equality in the relativistic entity (E/c)^2=m^2c^2+p^2 appears to be broken and even the energy is not definite positive. The latter is an underlying reason for the 'run-away' solution. The other choice is to require the radiation force to be orthogonal to the 4-momentum (not to the 4-velocity). In this case the energy and momentum are well-defined and obey the relationship (E/c)^2=m^2c^2+p^2. Remarkably, the equations of a particle's motion in this case differ significantly from all the known versions. They appear to be well founded. They are simple, easy to solve, and can be applied to simulate the particle motion in the focus of an ultra-bright laser.

We report on results of theoretical analysis of possibilities of light strong (Anderson) localization in a cold atomic ensemble. We predict appearance of localization in dense atomic systems in strong magnetic field. We prove that in absence of the field the light localization is impossible.

This paper investigates the interaction of an initially uniform magnetic field with an electrically conducting slab that moves perpendicularly to the magnetic field with arbitrary time-dependent velocity. It is demonstrated that the problem of determining the time-dependent Lorentz force and the time-dependent Joule heat in the slab is mathematically equivalent to solving a 1-D heat diffusion problem with time-dependent boundary conditions and to submitting the solution to a nonstandard postprocessing procedure. For the particular case of an impulsively driven slab we exploit the mathematical analogy between magnetic diffusion and heat diffusion by translating a textbook solution of the corresponding heat-transfer problem into exact and previously unknown relations for Lorentz force and Joule heat. Moreover, we use a 1-D finite-difference code to investigate more general time dependencies of the velocity including smooth accelerations and random velocity changes. Our numerical determination of reaction times (T 98 ) of the Lorentz force in the case of smooth accelerations provides a useful design tool for the development of Lorentz force flowmeters with short reaction times.

In the present work, we test the predictions of the AWSoM model, a global extended-MHD model capable of calculating the propagation and turbulent dissipation of Alfv\'en waves in any magnetic topology, against high resolution spectra of the quiescent off-disk solar corona. Wave dissipation is the only heating mechanism assumed in this model. Combining 3D model results with the CHIANTI atomic database, we were able to create synthetic line-of-sight spectra which include the effects of emission line broadening due to both thermal and wave-related non-thermal motions. To the best of our knowledge this is the first time a global model is used to obtain synthetic non-thermal line broadening. We obtained a steady-state solution driven by a synoptic magnetogram and compared the synthetic spectra with SUMER observations of a quiescent area above the solar west limb extending between 1.04 and 1.34 solar radii at the equator. Both the predicted line widths and the total line fluxes were consistent with the observations for 5 different ions. Using the 3D solution, we were able to locate the region that contributes the most to the emission used for measuring electron properties; we found that region to be a pseudo-streamer, whose modeled electron temperature and density are consistent with the measured ones. We conclude that the turbulent dissipation assumed in the AWSoM model can simultaneously account for the observed heating rate and the non-dissipated wave energy observed in this region., Comment: Submitted to the Astrophysical Journal

We carry out the first time-dependent numerical MagnetoHydroDynamic modeling of an extrasolar planetary system to study the interaction of the stellar magnetic field and wind with the planetary magnetosphere and outflow. We base our model on the parameters of the HD 189733 system, which harbors a close-in giant planet. Our simulation reveals a highly structured stellar corona characterized by sectors with different plasma properties. The star-planet interaction varies in magnitude and complexity, depending on the planetary phase, planetary magnetic field strength, and the relative orientation of the stellar and planetary fields. It also reveals a long, comet-like tail which is a result of the wrapping of the planetary magnetospheric tail by its fast orbital motion. A reconnection event occurs at a specific orbital phase, causing mass loss from the planetary magnetosphere that can generate a hot spot on the stellar surface. The simulation also shows that the system has sufficient energy to produce hot-spots observed in Ca II lines in giant planet hosting stars. However, the short duration of the reconnection event suggests that such SPI cannot be observed persistently., Submitted to ApJ, 14 pages, 9 figures

The generation of optical phase oscillations is investigated in an interferometer using a ${\text{Bi}}_{12}{\text{SiO}}_{20}$ non-steady-state photoelectromotive-force detector. Phase modulation of the signal optical beam is created by the detected signal itself, in contrast to the standard forced regime where such modulation is produced by an external source. The conditions necessary for the self-excitation of the oscillations are obtained using the results of the small-signal approach for the non-steady-state photoelectromotive-force effect. The amplitude and frequency of the oscillations are defined by the photoelectric properties of the detector but not by the feedback loop. The dependencies of the oscillations on the time and gain factor are measured for both the diffusion and drift regimes.

The extremely strong fields produced by focusing powerful laser pulses into minute volumes of material enable relativistic effects to be used to generate radiation, to accelerate particles, and to produce electrons and positrons from vacuum. From applications using existing high-repetition-rate lasers to those projected for super intense systems, the individual and collective behavior of electrons is the hub of both practical and theoretical directions. This report reviews work directed toward the application of positron generation from laser interaction with matter and vacuum. It spans funded original experimental research in laser-plasma interaction, where electrons dominate energy transport and MeV/micrometer fields are revealed, to theoretical collaborations exploring the connection between present and foreseeable lasers to the quantum electrodynamics of radiating electrons and electron-positron pair production from vacuum.

*† ‡ § # Solar energetic particles often get accelerated to energies up to few GeV at interplanetary shock waves driven by Coronal Mass Ejections (CMEs) and are of considerable importance for space weather studies because they can produce radiation hazards for manned or unmanned spacecraft. Particles accelerated at the shock wave can escape upstream and downstream into the interplanetary medium. As the escaped high-energy particles propagate along the interplanetary magnetic field, they are scattered by fluctuations of the turbulent magnetic field. The Monte-Carlo method has been adopted in this work to study propagation and scattering of solar energetic particles. We have demonstrated that high energy particles reach the orbit of the Earth before the bulk flow, which due to its high intensity produces main hazard. The detection of high energy particles may serve as a precursor of its arrival. I. Introduction The solar energetic particle (SEP) events associated with coronal mass ejections (CMEs) are of particular importance for space weather studies. High energy solar protons (~ few GeV) can be accelerated within a short period of time (≤1 hr) after the initiation of solar eruptions, which makes them difficult to predict, and pose a serious concern for the design and operation of both manned and unmanned space missions. Recent theories and related observations 1−7 suggest that these high-energy particles are the result of the first-order Fermi acceleration process 8 at a shock wave driven by a solar eruption, the so-called diffusive shock acceleration (DSA), in the Sun’s proximity (2–15 R : ). These theories, however, have been debated within the community 9−11 because very little is known about the dynamical properties of CME driven shock waves in the inner corona soon after the onset of the eruption and whether or not the level of turbulence at the shock is sufficient for this mechanism to work.

The working principle of Lorentz force velocimetry (LFV) is based on a linear dependence between measured force and velocity. We consider a case when a violation of that linear law takes place in order to take this effect into account for LFV. The response of the Lorentz force to a time-dependent velocity of solid conducting rods is experimentally studied. Solid conductors were chosen due to the fact that at a limited length of imposed magnetic field the end effects of secondary field generation are identical both in liquid and solid conductors. Thus one can simulate clearly a distortion of the imposed magnetic field in the case of non-stationary fluid flows. The magnetic Reynolds number based on advection time was of the order of unity. It is demonstrated that magnetic field advection effects lead to a Lorentz force difference in low- and finite- cases. The induced magnetic field measurements and experimental estimation of the eddy current density are reported.

We describe, analyze and validate the recently developed Alfv\'en Wave Solar Model (AWSoM), a 3D global model starting from the top of the chromosphere and extending into interplanetary space (up to 1-2 AU). This model solves the extended two temperature magnetohydrodynamics equations coupled to a wave kinetic equation for low frequency Alfv\'en waves. In this picture, heating and acceleration of the plasma are due to wave dissipation and wave pressure gradients, respectively. The dissipation process is described by a fully developed turbulent cascade of counter-propagating waves. We adopt a unified approach for calculating the wave dissipation in both open and closed magnetic field lines, allowing for a self-consistent treatment of any magnetic topology. Wave dissipation is the only heating mechanism assumed in the model, and no geometric heating functions are invoked. Electron heat conduction and radiative cooling are also included. We demonstrate that the large-scale, steady-state (in the co-rotating frame) properties of the solar environment are reproduced, using three adjustable parameters: the Poynting flux of chromospheric Alfv\'en waves, the perpendicular correlation length of the turbulence, and a pseudo-reflection coefficient. We compare model results for Carrington Rotation 2063 (November-December 2007) to remote observations in the EUV and X-ray ranges from STEREO, SOHO and Hinode spacecraft, as well as to in-situ measurements performed by Ulysses. The model results are in good agreement with observations. This is the first global model capable of simultaneously reproducing the multi-wavelength observations of the lower corona and the wind structure beyond Earth's orbit.

Ultra-strong laser pulses can be so intense that an electron in the focused beam loses significant energy due to gamma-photon emission while its motion deviates via the radiation back-reaction. Numerical methods and tools designed to simulate radiation-dominated and QED-strong laser-plasma interactions are summarized here.

We derive a modified non-perturbative Lorentz-Abraham-Dirac equation. It satisfies the proper conservation laws, particularly, it conserves the generalized momentum, the latter property eliminates the symmetry-breaking runaway solution. The equation allows a consistent calculation of the electron current, the radiation effect on the electron momentum, and the radiation itself, for a single electron or plasma electrons in strong electromagnetic fields. The equation is applied to a simulation of a strong laser pulse interaction with a plasma target. Some analytical solutions are also provided.