Motion Of Quantum Particles Research Articles

Effective quantum dynamics in curved thin-layer systems with inhomogeneous confinement

The motion of quantum particles homogeneously constrained to a curved surface is affected by a curvature-induced geometric potential. Here, by extending the thin-layer procedure, we consider the case of inhomogeneous confinement and derive the effective Hamiltonian where an extra effective potential appears. This effective potential is relevant to the ground-state energy perpendicular to the surface and the morphology of the confining potential. Tiny fluctuations in the thickness are envisioned to induce considerable magnitude of the effective potential. To demonstrate the impact of the inhomogeneity, we apply our method to investigate the coherent transport on a cylindrical surface where two helical ditches is imposed on the thickness. Numerical analysis reveals that the inhomogeneity of the confinement significantly affects the transport properties through changing the geometric symmetry of the system. This study develops the method for low-dimensional constrained systems and exhibits the possibility of a new degree of control for waveguiding in nanostructures.

Prüfer transformation and its application to the numerical description of the motion of quantum particles with various spins in the fields of classical black holes

Stable and reliable numerical integration of second-order radial equations in the fields of classical black holes can be performed by using the Pr\"ufer transformation and by passing to the use of phase functions, which allows uniquely selecting the solutions with physical asymptotics in numerical calculations.

Self-oscillating pump in a topological dissipative atom–cavity system

Pumps are transport mechanisms in which direct currents result from a cyclic evolution of the potential1,2. As Thouless showed, the pumping process can have topological origins, when considering the motion of quantum particles in spatially and temporally periodic potentials3. However, the periodic evolution that drives these pumps has always been assumed to be imparted from outside, as has been the case in the experimental systems studied so far4-12. Here we report on an emergent mechanism for pumping in a quantum gas coupled to an optical resonator, where we observe a particle current without applying a periodic drive. The pumping potential experienced by the atoms is formed by the self-consistent cavity field interfering with the static laser field driving the atoms. Owing to dissipation, the cavity field evolves between its two quadratures13, each corresponding to a different centrosymmetric crystal configuration14. This self-oscillation results in a time-periodic potential analogous to that describing the transport of electrons in topological tight-binding models, such as the paradigmatic Rice-Mele pump15. In the experiment, we directly follow the evolution by measuring the phase winding of the cavity field with respect to the driving field and observing the atomic motion in situ. The observed mechanism combines the dynamics of topological and open systems, and features characteristics of continuous dissipative time crystals.

Signatures of discrete time-crystallinity in transport through an open Fermionic chain

Discrete time-crystals are periodically driven quantum many-body systems with broken discrete time translational symmetry, a non-equilibrium steady state representing self-organization of motion of quantum particles. Observations of discrete time-crystalline order are currently limited to magneto-optical experiments and it was never observed in a transport experiment performed on systems connected to external electrodes. Here we demonstrate that both discrete time-crystal and quasi-crystal survive a very general class of environments corresponding to single-particle gain and loss through system-electrode coupling over experimentally relevant timescales. Using dynamical symmetries, we analytically identify the conditions for observing time-crystalline behavior in a periodically driven open Fermi-Hubbard chain attached to electrodes. We show that the spin-polarized transport current directly manifests the existence of a time-crystalline behavior. Our findings are verifiable in present-day experiments with quantum-dot arrays and Fermionic ultra-cold atoms in optical lattices.

Simulating angular momentum of gravitational field of a rotating black hole and spin momentum of gravitational waves

In this research, we simulated the angular momentum of gravitational field of a rotating black hole and the spin momentum of gravitational waves emitted from the black hole. At first, we calculated energy densities of the rotating gravitational field and spinning gravitational waves as the vectors, which were projected on the spherical curved surface of the gravitational field and of the gravitational waves. Then we calculated the angular momentum and the spin momentum as the vectors perpendicular to the curved surface. The earlier research by Paul Dirac, published in 1964, did not select the curved surface to calculate the motion of quantum particles; but, instead, he chose the flat surface to develop the theory of quantum mechanics. However, we pursued the simulation of the gravitational waves in spherical polar coordinates that form the spherical curved surface of the gravitational waves. As a result, we found that a set of anti-symmetric vectors described the vectors that were perpendicular to the spherical curved surface, and with these vectors we simulated the angular momentum of the rotating black hole’s gravitational field and the spin momentum of gravitational waves. The obtained results describe the characteristics of the rotation of a black hole and of spinning gravitational waves.

Quantum particle motion on the surface of a helicoid in the presence of an harmonic oscillator

The geometric potential in quantum mechanics has been attracted attention recently, providing a formalism to investigate the influence of curvature in the context of low-dimensional systems. In this paper, we study the consequences of a helicoidal geometry in the Schrödinger equation dealing with an anisotropic mass tensor. In particular, we solve the problem of an harmonic oscillator in this scenario. For some specific conditions, we determine the wavefunction in terms of Confluent Heun Functions and compute the respective energy. The system exhibit several different behaviors, depending on the adjustment on the mass components.

Restoring geometrical optics near caustics using sequenced metaplectic transforms

Geometrical optics (GO) is often used to model wave propagation in weakly inhomogeneous media and quantum-particle motion in the semiclassical limit. However, GO predicts spurious singularities of the wavefield near reflection points and, more generally, at caustics. We present a new formulation of GO, called metaplectic geometrical optics (MGO), that is free from these singularities and can be applied to any linear wave equation. MGO uses sequenced metaplectic transforms of the wavefield, corresponding to symplectic transformations of the ray phase space, such that caustics disappear in the new variables and GO is reinstated. The Airy problem and the quantum harmonic oscillator are described analytically using MGO for illustration. In both cases, the MGO solutions are remarkably close to the exact solutions and remain finite at cutoffs, unlike the usual GO solutions.

English

English

Entangled Quantum Dynamics of Many-Body Systems using Bohmian Trajectories

Bohmian mechanics is an interpretation of quantum mechanics that describes the motion of quantum particles with an ensemble of deterministic trajectories. Several attempts have been made to utilize Bohmian trajectories as a computational tool to simulate quantum systems consisting of many particles, a very demanding computational task. In this paper, we present a novel ab-initio approach to solve the many-body problem for bosonic systems by evolving a system of one-particle wavefunctions representing pilot waves that guide the Bohmian trajectories of the quantum particles. In this approach, quantum entanglement effects arise due to the interactions between different configurations of Bohmian particles evolving simultaneously. The method is used to study the breathing dynamics and ground state properties in a system of interacting bosons.

Non-Markovian quantum Brownian motion in one dimension in electric fields

Quantum Brownian motion is the random motion of quantum particles suspended in a field (or an effective field) resulting from their collision with fast-moving modes in the field. It provides us with a fundamental model to understand various physical features concerning open systems in chemistry, condensed-matter physics, biophysics, and optomechanics. In this paper, without either the Born-Markovian or rotating-wave approximation, we derive a master equation for a charged-Brownian particle in one dimension coupled with a thermal reservoir in electric fields. The effect of the reservoir and the electric fields is manifested as time-dependent coefficients and coherent terms, respectively, in the master equation. The two-photon correlation between the Brownian particle and the reservoir can induce nontrivial squeezing dynamics to the particle. We derive a current equation including the source from the driving fields, transient current from the system flowing into the environment, and the two-photon current caused by the non-rotating-wave term. The presented results then are compared with that given by the rotating-wave approximation in the weak-coupling limit, and these results are extended to a more general quantum network involving an arbitrary number of coupled-Brownian particles. The presented formalism might open a way to better understand exactly the non-Markovian quantum network.

Unification of Classical Mechanics and Quantum Mechanics in Unique Conception of Particle Dynamics

It is shown that motion of quantum particles and classical particles can be described in the framework of the same formalism. Stochasticity of particle motion depends on the form of the space-time geometry, which is to be described as a physical geometry, i.e. a geometry obtained as a result of deformation of the proper Euclidean geometry. The new method of the particle motion description does not use quantum principles. It admits one to use the structural approach to theory of elementary particles. The structural approach admits one to consider structure and arrangement of elementary particles, that cannot been obtained at conventional approach, using quantum principles.

Pilot-Wave Quantum Theory in Discrete Space and Time and the Principle of Least Action

The idea of obtaining a pilot-wave quantum theory on a lattice with discrete time is presented. The motion of quantum particles is described by a $|\Psi|^2$-distributed Markov chain. Stochastic matrices of the process are found by the discrete version of the least-action principle. Probability currents are the consequence of Hamilton's principle and the stochasticity of the Markov process is minimized. As an example, stochastic motion of single particles in a double-slit experiment is examined.

Scattering approach to the thermodynamics of quantum transport

The thermodynamic entropy production for the scattering processes of noninteracting bosons and fermions in mesoscopic systems is shown to be related to the difference between the Connes–Narnhofer–Thirring entropy per unit time, characterizing temporal disorder in the motion of quantum particles, and the associated time-reversed coentropy per unit time. Under nonequilibrium conditions, the positivity of thermodynamic entropy production can thus be interpreted as a time-reversal symmetry breaking in the temporal disorder of the quantum transport process. Moreover, the full counting statistics of both fermionic and bosonic quantum transport is formulated in relation with the energy and particle currents producing thermodynamic entropy in nonequilibrium steady states.

Phase space dynamics and control of the quantum particles associated to hypergraph states

As today's nanotechnology focus becomes primarily oriented toward production and manipulation of materials at the subatomic level, allowing the performance and complexity of interconnects where the device density accepts more than hundreds devices on a single chip, the manipulation of semiconductor nanostructures at the subatomic level sets its prime tasks on preserving and adequate transmission of information encoded in specified (quantum) states. The presented study employs the quantum communication protocol based on the hypergraph network model where the numerical solutions of equations of motion of quantum particles are associated to vertices (assembled with device chip), which follow specific controllable paths in the phase space. We address these findings towards ultimate quest for prediction and selective control of quantum particle trajectories. In addition, presented protocols could represent valuable tool for reducing background noise and uncertainty in low-dimensional and operationally meaningful, scalable complex systems.

Computational method for the long time propagation of quantum channeled particles in crystals and carbon nanotubes

This work reports on the computational method for the long time propagation of the quantum channeled particles in infinite and finite harmonic interaction wells and in a realistic carbon nanotube interaction potential well. This method is based on the Chebyshev global propagation method for solving of the corresponding time dependent Schrödinger equation. For comparison, the computational method based on the Crank–Nicolson propagation method is also presented. In the case of quantum particle motion in infinite harmonic potential well, when the analytical solution of the corresponding time-dependent Schrödinger equation exists, we show that the obtained propagation method is efficient, very accurate and numerically stable. It is superior with respect to the method based on the Crank–Nicolson propagation method. A detailed study of the long time quantum particle motion in the finite harmonic interaction potential well shows that the obtained computational method based on the Chebyshev global propagation method can be successfully applied for following of the channeled quantum particle in crystals and carbon nanotubes. This is demonstrated in the case of quantum particle motion in a realistic carbon nanotube interaction potential well.

Quantum particle motion in physical space

Using Feynman's representation of the quantum evolution and considering a quantum particle as a matter field (continuous medium), it is shown that individual particles of the field have unique paths of the motion. This allows describing motion of the quantum particle continuous medium by Lagrange's method. It is shown that form of the real individual particle path is determined by classical minimum action principle.

The Snell law for quaternionic potentials

By using the analogy between optics and quantum mechanics, we obtain the Snell law for the planar motion of quantum particles in the presence of quaternionic potentials.

Global Optimization by Quantum Dynamics with Energy Dissipation

Both reduction in computational load and setting parameters with ease are necessary in calculation of global optimization. For this we propose a new quantum mechanical method of the problem. Global optimization is achieved by a quantum particle with energy dissipation due to frictional force. Canonical quantization is applied to a system that consists of one mass point under friction proportional to its velocity. Realistic motion of a particle is abstracted from a resultant quantum system according to a causal interpretation. By simulation of the quantum particle motion under potential functions V(x) with local minima and one global minimum, it is clarified that the particle with its initial position at the local minimum at rest necessarily arrives at the global minimum. Only one particle is needed in the new algorithm. When we clarify mathematical structure of our algorithm, difficulties found in quantum annealing or conventional method for global optimization will thereby be solved in the new method.

A quantum particle motion and thermodynamics in faults-defects field: Path integral formulation based on extended deformation gradient tensor

We consider the effect of the faults-defects (FD) field on the following quantum phenomena: (i) the motion of a particle expressed by the Green function; (ii) thermodynamic phenomena expressed by the partition function. We use the path integral formulation based on the extended deformation gradient (EDG) tensor. This formulation connects the Green function of (i) with the partition function of (ii) to describe the thermodynamics in terms of a quantum particle motion. We obtain the following results: (a) The Lagrangian in the Green function includes the new potential consisting of stress functions that shift the path of the free particle from the shortest distance; (b) The solution of the partition function in one-dimensional space makes it possible to deduce the thermodynamic relations in the FD field. Such results could not be obtained by taking the traditional mechanical and quantum approaches, so the path integral formulation based on the EDG tensor is a useful tool.

Infinite quantum well: A coherent state approach

A new family of 2-component vector-valued coherent states for the quantum particle motion in an infinite square well potential is presented. They allow a consistent quantization of the classical phase space and observables for a particle in this potential. We then study the resulting position and (well-defined) momentum operators. We also consider their mean values in coherent states and their quantum dispersions.