Space Fractional Quantum Mechanics Research Articles

One-dimensional Lévy quasicrystal

Space-fractional quantum mechanics (SFQM) is a generalization of the standard quantum mechanics when the Brownian trajectories in Feynman path integrals are replaced by Lévy flights. We introduce Lévy quasicrystal by discretizing the space-fractional Schrödinger equation using the Grünwald–Letnikov derivatives and adding on-site quasiperiodic potential. The discretized version of the usual Schrödinger equation maps to the Aubry–André (AA) Hamiltonian, which supports localization–delocalization transition even in one dimension. We find the similarities between Lévy quasicrystal and the AA model with power-law hopping, and show that the Lévy quasicrystal supports a delocalization–localization transition as one tunes the quasiperiodic potential strength and shows the coexistence of localized and delocalized states separated by mobility edge. Hence, a possible realization of SFQM in optical experiments should be a new experimental platform to test the predictions of AA models in the presence of power-law hopping.

Quantum tunneling from family of Cantor potentials in fractional quantum mechanics

We explore the features of non-relativistic quantum tunneling in space fractional quantum mechanics through a family of Cantor potentials. We consider two types of potentials: general Cantor and general Smith–Volterra–Cantor potential. The Cantor potential is an example of fractal potential while the Smith-Volterra–Cantor potential does not belong to the category of a fractal system. The present study brings for the first time, the study of quantum tunneling through fractal potential in fractional quantum mechanics. We report several new features of scattering in the domain of space fractional quantum mechanics including the emergence of energy-band like features from these systems and extremely sharp transmission features. Further the scaling relation of the scattering amplitude with wave vector k is presented analytically for both types of potentials.

Tunneling time from locally periodic potential in space fractional quantum mechanics

We calculate the time taken by a wave packet to travel through a classically forbidden locally periodic rectangular potential in space fractional quantum mechanics (SFQM). We obtain the closed-form expression of tunneling time from such a potential by stationary phase method. We show that tunneling time depends upon the width b of the single barrier and separation L between the barriers in the limit $$b \rightarrow \infty $$ and therefore generalized Hartman effect does not exist in SFQM. We observe that in SFQM, the tunneling time for large b in the case of locally periodic potential is smaller than the tunneling from a single barrier of the same width b. It is further shown that with the increase in barrier numbers, the tunneling time reduces in SFQM in the limit of large b.

New scattering features in non-Hermitian space fractional quantum mechanics

The spectral singularity (SS) and coherent perfect absorption (CPA) have been extensively studied over the last one and half decade for different non-Hermitian potentials in non-Hermitian standard quantum mechanics (SQM) governed by Schrödinger equation. In the present work we explore these scattering features in the domain of non-Hermitian space fractional quantum mechanics (SFQM) governed by fractional Schrödinger equation which is characterized by Levy index α (1<α≤2). We observe that non-Hermitian SFQM systems have more flexibility for SS and CPA and display some new features of scattering. For the delta potential V(x)=iρδ(x−x0), ρ>0, the SS energy, Ess, is blue or red shifted with decreasing α depending on the strength of the potential. For complex rectangular barrier in non-Hermitian SQM, it is known that the reflection and transmission amplitudes are oscillatory near the spectral singular point. It is found that these oscillations eventually develop SS in non-Hermitian SFQM. The similar features are also reported for the case of CPA phenomena from complex rectangular barrier in non-Hermitian SFQM. These observations suggest a deeper relation between scattering features of non-Hermitian SQM and non-Hermitian SFQM.

Tunneling time in space fractional quantum mechanics

We calculate the time taken by a wave packet to travel through a classically forbidden region of space in space fractional quantum mechanics. We obtain the close form expression of tunneling time from a rectangular barrier by stationary phase method. We show that tunneling time depends upon the width b of the barrier for b→∞ and therefore Hartman effect doesn't exist in space fractional quantum mechanics. Interestingly we found that the tunneling time monotonically reduces with increasing b. The tunneling time is smaller in space fractional quantum mechanics as compared to the case of standard quantum mechanics. We recover the Hartman effect of standard quantum mechanics as a special case of space fractional quantum mechanics.

Definition of the Riesz derivative and its application to space fractional quantum mechanics

We investigate and compare different representations of the Riesz derivative, which plays an important role in anomalous diffusion and space fractional quantum mechanics. In particular, we show that a certain representation of the Riesz derivative, Rxα, that is generally given as also valid for α = 1, behaves no differently than the other definition given in terms of its Fourier transform. In the light of this, we discuss the α → 1 limit of the space fractional quantum mechanics and its consistency.

The most general form of deformation of the Heisenberg algebra from the generalized uncertainty principle

In this paper, we will propose the most general form of the deformation of Heisenberg algebra motivated by the generalized uncertainty principle. This deformation of the Heisenberg algebra will deform all quantum mechanical systems. The form of the generalized uncertainty principle used to motivate these results will be motivated by space fractional quantum mechanics and non-locality in quantum mechanical systems. We also analyse a specific limit of this generalized deformation for one dimensional system, and in that limit, a nonlocal deformation of the momentum operator generates a local deformation of all one dimensional quantum mechanical systems. We analyse the low energy effects of this deformation on a harmonic oscillator, Landau levels, Lamb shift, and potential barrier. We also demonstrate that this deformation leads to a discretization of space.

Transmission through locally periodic potentials in space-fractional quantum mechanics

We study transmission through locally periodic potentials in the framework of space-fractional quantum mechanics (SFQM). In particular, we calculate the transmission probabilities T(N) for a particle in a chain of N Dirac-δ barriers and, for the other case, a chain of N square barriers. We use a transfer-matrix (M-matrix) approach in the context of SFQM to obtain equations for T(N). For both systems, bandlike structures emerge even for a small number of barriers of as low as N=4 and are more apparent for lower values of Lévy index α considered.

Potential condensed-matter realization of space-fractional quantum mechanics: The one-dimensional Lévy crystal

We introduce and discuss the one-dimensional Lévy crystal as a probable candidate for an experimentally accessible realization of space-fractional quantum mechanics (SFQM) in a condensed-matter environment. The discretization of the space-fractional Schrödinger equation with the help of shifted Grünwald-Letnikov derivatives delivers a straightforward route to define the Lévy crystal of order αε(1,2]. As key ingredients for its experimental identification we study the dispersion relation as well as the density of states for arbitrary αε(1,2]. It is demonstrated that in the limit of small wave numbers all interesting properties of continuous-space SFQM are recovered, while for α→2 the well-established nearest-neighbor one-dimensional tight-binding chain arises.

Space fractional Wigner equation and its semiclassical limit

Manifestations of space fractional quantum mechanics (SFQM), as it was formulated by Laskin [Phys. Rev. E 62, 3135 (2000)], are deemed to offer a better physical interpretation of Lévy flight statistics on a quantum mechanical level. We start with the SFQM Schrödinger equation characterized by a Lévy flight index α∈ (1,2), perform a Wigner transform, and draw the limit h/Eτ → 0 (i.e., let the observed energy scale E go to infinity in comparison to the quantization given by h/τ). In order to obtain classical transport equations two possible substitutions for the terms |p|(α) and |p'|α which appear in von Neumann's equation are presented. It is demonstrated that they conform to the criteria for a successful Wigner transform. Their benefits and caveats are discussed in detail. We find, that, indeed, SFQM manifests itself in an anomalous kinetic term of the free particle's motion and, assuming an external potential diagonal in momentum space for the sake of simplicity, in corresponding anomalous terms in the resulting drift current. All our results reduce to the classical forms in the limit α = 2.

Applications of density matrix in the fractional quantum mechanics: Thomas–Fermi model and Hohenberg–Kohn theorems revisited

The many-body space fractional quantum system is studied using the density matrix method. We give the new results of the Thomas–Fermi model, obtain the quantum pressure of the free electron gas. We also show the validity of the Hohenberg–Kohn theorems in the space fractional quantum mechanics and generalize the density functional theory to the fractional quantum mechanics.