Framework Of Quantum Mechanics Research Articles

Quantization of Liénard's nonlinear harmonic oscillator and its solutions in the framework of supersymmetric quantum mechanics

Liénard-type nonlinear one dimensional oscillator is quantized using van Roos symmetric ordering recipe for the kinetic-like part of the new derived Hamiltonian. The corresponding Schrödinger equation is exactly solved in momentum space via the approach of supersymmetric quantum mechanics (SUSYQM). The bound-states energy spectra and corresponding wave functions are given explicitly in terms of the ambiguity parameters. The limiting case of no deformation agrees exactly with the eigenenergies and eigenfunctions of the ordinary quantum harmonic oscillator.

Quantum gravity: a quantum-first approach

A “quantum-first” approach to gravity is described, where rather than quantizing gen- eral relativity, one seeks to formulate the physics of gravity within a quantum-mechanical framework with suitably general postulates. Important guides are the need for appropri- ate mathematical structure on Hilbert space, and correspondence with general relativity and quantum field theory in weak-gravity situations. A basic physical question is that of “Einstein separability:” how to define mutually independent subsystems, e.g. through localization. Standard answers via tensor products or operator algebras conflict with prop- erties of gravity, as is seen in the correspondence limit; this connects with discussions of “soft hair.” Instead, gravitational behavior suggests a networked Hilbert space structure. This structure plus unitarity provide important clues towards a quantum formulation of gravity.

Semiclassical and quantum behavior of the Mixmaster model in the polymer approach for the isotropic Misner variable

We analyze the semi-classical and quantum behavior of the Bianchi IX Universe in the Polymer Quantum Mechanics framework, applied to the isotropic Misner variable, linked to the space volume of the model. The study is performed both in the Hamiltonian and field equations approaches, leading to the remarkable result of a still singular and chaotic cosmology, whose Poincaré return map asymptotically overlaps the standard Belinskii–Khalatnikov–Lifshitz one. In the quantum sector, we reproduce the original analysis due to Misner, within the revised Polymer approach and we arrive to demonstrate that the quantum numbers of the point-Universe still remain constants of motion. This issue confirms the possibility to have quasi-classical states up to the initial singularity. The present study clearly demonstrates that the asymptotic behavior of the Bianchi IX Universe towards the singularity is not significantly affected by the Polymer reformulation of the spatial volume dynamics both on a pure quantum and a semiclassical level.

Electronic structure calculations for rhenium carbonitride: an extended Hückel tight-binding study

Effective theoretical models are needed to predict the physical properties of materials. Here we discuss the electronic structure of rhenium carbonitride (ReCN) in terms of tight-binding. The extended Hückel tight-binding (EHTB) formalism was employed to calculate the band structure, density of states (DOS) and investigate the chemical bonding properties as well as the crystal field splitting (CFS) of d orbitals in the Re atom. Two ReCN structures were studied, characterized by space groups P63mc and P3m1, respectively. The calculated energy bands and DOS depict semiconductor properties for both structures, seeing an indirect band-gap of 0.62 eV in P63mc (M − K) while a direct band-gap of 0.49 eV is seen in P3m1 at (H). Mulliken population and CFS analysis were done to gain insight into the filling of 5d orbitals in ReCN, crystallographical differences between the two crystal structures and their physical implications. The five-fold degenerate energy levels in both the P63mc and P3m1 structures are broken by a tetragonal crystal electric field. The P63mc structure undergoes Peierls distortion, resulting in a loss of symmetry. The EHTB method is an effective tool to approximate the physical and chemical properties of novel materials such as ReCN at a low computational cost and in terms of a simple quantum-mechanical framework, understood by the broader community. The EHTB model for ReCN will serve as a benchmark and starting point for future studies on the compound within similar contexts.

Large-scale tight-binding simulations of quantum transport in ballistic graphene

Graphene has proven to host outstanding mesoscopic effects involving massless Dirac quasiparticles travelling ballistically resulting in the current flow exhibiting light-like behaviour. A new branch of 2D electronics inspired by the standard principles of optics is rapidly evolving, calling for a deeper understanding of transport in large-scale devices at a quantum level. Here we perform large-scale quantum transport calculations based on a tight-binding model of graphene and the non-equilibrium Green’s function method and include the effects of p-n junctions of different shape, magnetic field, and absorptive regions acting as drains for current. We stress the importance of choosing absorbing boundary conditions in the calculations to correctly capture how current flows in the limit of infinite devices. As a specific application we present a fully quantum-mechanical framework for the ‘2D Dirac fermion microscope’ recently proposed by Bøggild et al (2017 Nat. Commun. 8 10.1038), tackling several key electron-optical effects therein predicted via semiclassical trajectory simulations, such as electron beam collimation, deflection and scattering off Veselago dots. Our results confirm that a semiclassical approach to a large extend is sufficient to capture the main transport features in the mesoscopic limit and the optical regime, but also that a richer electron-optical landscape is to be expected when coherence or other purely quantum effects are accounted for in the simulations.

Photoionization microscopy: Hydrogenic theory in semiparabolic coordinates and comparison with experimental results

Photoionization microscopy (PM) is an experimental method allowing for high-resolution measurements of the electron current probability density in the case of photoionization of an atom in an external uniform static electric field. PM is based on high-resolution velocity-map imaging and offers the unique opportunity to observe the quantum oscillatory spatial structure of the outgoing electron flux. We present the basic elements of the quantum-mechanical theoretical framework of PM for hydrogenic systems near threshold. Our development is based on the computationally more convenient semiparabolic coordinate system. Theoretical results are first subjected to a quantitative comparison with hydrogenic images corresponding to quasibound states and a qualitative comparison with nonresonant images of multielectron atoms. Subsequently, particular attention is paid on the structure of the electron's momentum distribution transversely to the static field (i.e., of the angularly integrated differential cross-section as a function of electron energy and radius of impact on the detector). Such 2D maps provide at a glance a complete picture of the peculiarities of the differential cross-section over the entire near-threshold energy range. Hydrogenic transverse momentum distributions are computed for the cases of the ground and excited initial states and single- and two-photon ionization schemes. Their characteristics of general nature are identified by comparing the hydrogenic distributions among themselves, as well as with a presently recorded experimental distribution concerning the magnesium atom. Finally, specificities attributed to different target atoms, initial states, and excitation scenarios are also discussed, along with directions of further work.

Multifold paths of neutrons in the three-beam interferometer detected by a tiny energy kick

A neutron optical experiment is presented to investigate the paths taken by neutrons in a three-beam interferometer. In various beam-paths of the interferometer, the energy of the neutrons is partially shifted so that the faint traces are left along the beam-path. By ascertaining an operational meaning to "the particle's path", which-path information is extracted from these faint traces with minimal-perturbations. Theory is derived by simply following the time evolution of the wave function of the neutrons, which clarifies the observation in the framework of standard quantum mechanics. Which-way information is derived from the intensity, sinusoidally oscillating in time at different frequencies, which is considered to result from the interfering cross terms between stationary main component and the energy-shifted which-way signals. Final results give experimental evidence that the (partial) wave functions of the neutrons in each beam path are superimposed and present in multiple locations in the interferometer.

Quantum Atomistic Approach for Interacting Spins

The phenomenological Landau theory of the spin precession has been used to reproduce the out-of-equilibrium properties of many magnetic systems. However, such an approach suffers from some serious limitations. The main reason is that the spin and the angular momentum of the atoms are described by the classical theory of the angular momentum. We derive a discrete model that extends the Landau theory to the quantum mechanical framework. Our approach is based on the application of the quantification procedure to the classical Hamiltonian of an array of interacting spins. The connection with the classical dynamics is discussed.

Quantum probe of Hořava-Lifshitz gravity

Particle probe analysis of the Kehagias-Sfetsos black hole spacetime of Hořava-Lifshitz gravity is extended to wave probe analysis within the framework of quantum mechanics. The time-like naked singularity that develops when ωM2 < 1/2 is probed with quantum fields obeying Klein-Gordon and Chandrasekhar-Dirac equations. The quantum field probe of the naked singularity has revealed that both the spatial part of the wave and the Hamiltonian operators of Klein-Gordon and Chandrasekhar-Dirac equations are essentially self-adjoint, and thus, the naked singularity in the Kehagias-Sfetsos spacetime becomes quantum mechanically non-singular.

Game theoretic security of quantum bit commitment

Due to the threat posed by quantum computing, there has been an increasingly focus on designing secure and efficient quantum-based and post-quantum cryptographic protocols. In this paper, we study and propose a quantum bit commitment (QBC) protocol inspired by the framework of categorical quantum mechanics. We show that our protocol is more secure and simpler than most existing cheat-sensitive QBC protocols. Then, we introduce the notion of game theoretic security, and demonstrate that such a notion is less demanding than unconditional security, yet stricter than cheat-sensitive. We show that our protocol is game theoretic secure for many commitment games. Being game theoretic secure opens the door of applying our protocol to game theory. Specifically, we show that our protocol can be used to implement equilibrium in commitment games. Finally, we run experiments on the IBM quantum computer to demonstrate the practicability of our protocol.

No-Go Theorems and the Foundations of Quantum Physics

In the history of quantum physics several no-go theorems have been proved, and many of them have played a central role in the development of the theory, such as Bell’s or the Kochen–Specker theorem. A recent paper by F. Laudisa has raised reasonable doubts concerning the strategy followed in proving some of these results, since they rely on the standard framework of quantum mechanics, a theory that presents several ontological problems. The aim of this paper is twofold: on the one hand, I intend to reinforce Laudisa’s methodological point by critically discussing Malament’s theorem in the context of the philosophical foundation of quantum field theory; secondly, I rehabilitate Gisin’s theorem showing that Laudisa’s concerns do not apply to it.

Automated reaction path searches for spin-forbidden reactions.

Many catalytic and biomolecular reactions containing transition metals involve changes in the electronic spin state. These processes are referred to as "spin-forbidden" reactions within nonrelativistic quantum mechanics framework. To understand detailed reaction mechanisms of spin-forbidden reactions, one must characterize reaction pathways on potential energy surfaces with different spin states and then identify crossing points. Here we propose a practical computational scheme, where only the lowest mixed-spin eigenstate obtained from the diagonalization of the spin-coupled Hamiltonian matrix is used in reaction path search calculations. We applied this method to the 6,4 FeO+ + H2 → 6,4 Fe+ + H2 O, 6,4 FeO+ + CH4 → 6,4 Fe+ + CH3 OH, and 7 Mn+ + OCS → 5 MnS+ + CO reactions, for which crossings between the different spin states are known to play essential roles in the overall reaction kinetics. © 2018 Wiley Periodicals, Inc.

The relative error of calculations at the Pöschl-Teller model potential for the planar channeled muon

In the framework of quantum mechanics, we investigate muon channeling in the Si (200) crystal. The transverse energy levels and wave functions are obtained for the Pöschl-Teller and the Doyle-Turner potentials. Comparative analysis demonstrates that analytical results of calculations obtained on the base of the Pöschl-Teller potential are in a good agreement with the numerical results of calculations in the Doyle-Turner model for the low energy levels. These results for the muon with rest mass mμ and relativistic factor γ are valid for any particle with elementary charge and rest mass m and relativistic factor γm = γ (mμ/m). Therefore, our results can be useful for the preparation and performing the experimental investigation of the various phenomena accompanying particle channeling.

Frontiers of Theoretical Research on Shape Memory Alloys: A General Overview

In this concise review, general aspects of modeling shape memory alloys (SMAs) are recounted. Different approaches are discussed under four general categories, namely, (a) macro-phenomenological, (b) micromechanical, (c) molecular dynamics, and (d) first principles models. Macro-phenomenological theories, stemming from empirical formulations depicting continuum elastic, plastic, and phase transformation, are primarily of engineering interest, whereby the performance of SMA-made components is investigated. Micromechanical endeavors are generally geared towards understanding microstructural phenomena within continuum mechanics such as the accommodation of straining due to phase change as well as role of precipitates. By contrast, molecular dynamics, being a more recently emerging computational technique, concerns attributes of discrete lattice structures, and thus captures SMA deformation mechanism by means of empirically reconstructing interatomic bonding forces. Finally, ab initio theories utilize quantum mechanical framework to peek into atomistic foundation of deformation, and can pave the way for studying the role of solid-sate effects. With specific examples, this paper provides concise descriptions of each category along with their relative merits and emphases.

Towards Quantum Field Theory in Categorical Quantum Mechanics

In this work, we use tools from non-standard analysis to introduce infinite-dimensional quantum systems and quantum fields within the framework of Categorical Quantum Mechanics. We define a dagger compact category *Hilb suitable for the algebraic manipulation of unbounded operators, Dirac deltas and plane-waves. We cover in detail the construction of quantum systems for particles in boxes with periodic boundary conditions, particles on cubic lattices, and particles in real space. Not quite satisfied with this, we show how certain non-separable Hilbert spaces can also be modelled in our non-standard framework, and we explicitly treat the cases of quantum fields on cubic lattices and quantum fields in real space.

Magnetic monopoles and nonassociative deformations of quantum theory

We examine certain nonassociative deformations of quantum mechanics and gravity in three dimensions related to the dynamics of electrons in uniform distributions of magnetic charge. We describe a quantitative framework for nonassociative quantum mechanics in this setting, which exhibits new effects compared to ordinary quantum mechanics with sourceless magnetic fields, and the extent to which these theoretical consequences may be experimentally testable. We relate this theory to noncommutative Jordanian quantum mechanics, and show that its underlying algebra can be obtained as a contraction of the alternative algebra of octonions. The uncontracted octonion algebra conjecturally describes a nonassociative deformation of three-dimensional quantum gravity induced by magnetic monopoles, which we propose is realised by a non-geometric Kaluza-Klein monopole background in M-theory.

A Theory of Gravity and General Relativity based on Quantum Electromagnetism

Based on first principles solutions in a unified framework of quantum mechanics and electromagnetism we predict the presence of a universal attractive depolarisation radiation (DR) Lorentz force (F) between quantum entities, each being either an IED matter particle or light quantum, in a polarisable dielectric vacuum. Given two quantum entities i = 1, 2 of either kind, of characteristic frequencies , masses and separated at a distance r0, the solution for F is , where is the susceptibility and πλ is the reduced linear mass density of the vacuum. This force F resembles in all respects Newton’s gravity and is accurate at the weak F limit; hence ℊ equals the gravitational constant G. The DR wave fields and hence the gravity are each propagated in the dielectric vacuum at the speed of light c; these can not be shielded by matter. A test particle µ of mass m0 therefore interacts gravitationally with all of the building particles of a given large mass M at r0 apart, by a total gravitational force F = −GMm0/(r0)2 and potential V = −∂F/∂r0. For a finite V and hence a total Hamiltonian H = m0c2 + V, solution for the eigenvalue equation of µ presents a red-shift in the eigen frequency ν = ν0(1 − GM/r0c2) and hence in other wave variables. The quantum solutions combined with the wave nature of the gravity further lead to dilated gravito optical distance r = r0/(1 − GM/r0c2) and time t = t0/(1 − GM/r0c2), and modified Newton’s gravity and Einstein’s mass energy relation. Applications of these give predictions of the general relativistic effects manifested in the four classical test experiments of Einstein’s general relativity (GR), in direct agreement with the experiments and the predictions given based on GR.

Some clarifications about the Bohmian geodesic deviation equation and Raychaudhuri’s equation

One of the important and famous topics in general theory of relativity and gravitation is the problem of geodesic deviation and its related singularity theorems. An interesting subject is the investigation of these concepts when quantum effects are considered. Since the definition of trajectory is not possible in the framework of standard quantum mechanics (SQM), we investigate the problem of geodesic equation and its related topics in the framework of Bohmian quantum mechanics in which the definition of trajectory is possible. We do this in a fixed background and we do not consider the backreaction effects of matter on the space–time metric.

Undergraduate quantum mechanics: lost opportunities for engaging motivated students?

Quantum mechanics is widely recognised as an important and difficult subject, and many studies have been published focusing on students’ conceptual difficulties. However, the sociocultural aspects of studying such an emblematic subject have not been researched to any large extent. This study explores students’ experiences of undergraduate quantum mechanics using qualitative analysis of semi-structured interview data. The results inform discussions about the teaching of quantum mechanics by adding a sociocultural dimension. Students pictured quantum mechanics as an intriguing subject that inspired them to study physics. The study environment they encountered when taking their first quantum mechanics course was however not always as inspiring as expected. Quantum mechanics instruction has commonly focused on the mathematical framework of quantum mechanics, and this kind of teaching was also what the interviewees had experienced. Two ways of handling the encounter with a traditional quantum mechanics course were identified in the interviews; either students accept the practice of studying quantum mechanics in a mathematical, exercise-centred way or they distance themselves from these practices and the subject. The students who responded by distancing themselves experienced a crisis and disappointment, where their experiences did not match the way they imagined themselves engaging with quantum mechanics. The implications of these findings are discussed in relation to efforts to reform the teaching of undergraduate quantum mechanics.

Fission fragment mass and total kinetic energy distributions of spontaneously fissioning plutonium isotopes

The fission-fragment mass and total kinetic energy (TKE) distributions are evaluated in a quantum mechanical framework using elongation, mass asymmetry, neck degree of freedom as the relevant collective parameters in the Fourier shape parametrization recently developed by us. The potential energy surfaces (PES) are calculated within the macroscopic-microscopic model based on the Lublin-Strasbourg Drop (LSD), the Yukawa-folded (YF) single-particle potential and a monopole pairing force. The PES are presented and analysed in detail for even-even Plutonium isotopes with A = 236–246. They reveal deep asymmetric valleys. The fission-fragment mass and TKE distributions are obtained from the ground state of a collective Hamiltonian computed within the Born-Oppenheimer approximation, in the WKB approach by introducing a neck-dependent fission probability. The calculated mass and total kinetic energy distributions are found in good agreement with the data.