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arXiv:2605.05617

Static-Field Tunneling Ionization in Space-Fractional Quantum Mechanics

Marcelo F. Ciappina

quant-phphysics.atom-phSubmitted May 7, 2026• Announced May 8, 2026• 0 citations
arXivHTMLPDF

Abstract

Tunneling ionization in static or slowly varying electric fields is a cornerstone of strong-field physics and provides the entry point for semiclassical descriptions of above-threshold ionization and high-harmonic generation. In conventional quantum mechanics, the Perelomov--Popov--Terent'ev (PPT) theory and its Ammosov--Delone--Krainov (ADK) form yield an ionization rate whose defining feature is an exponential dependence governed by an under-barrier (imaginary-time) action. Here we develop an analytical ADK-like tunneling model within \emph{space-fractional} quantum mechanics, where the quadratic kinetic energy is replaced by the Riesz fractional Laplacian of order $1<α\le2$. Working in a static electric field in the length gauge, we derive a closed-form tunneling exponent for a triangular exit barrier. The fractional kinetic operator deforms the conventional $I_p^{3/2}$ scaling to $I_p^{1+1/α}$ and introduces a characteristic $\sin(π/α)$ factor encoding the complex-phase structure associated with nonlocal dispersion. We position this benchmark relative to prior tunneling studies in fractional quantum mechanics (primarily scattering through model barriers and fractal potentials) and provide a validation protocol for testing the exponent in time-dependent simulations of the fractional Schrödinger equation under a constant field. The result establishes a transparent reference for static-field ionization in nonlocal quantum dynamics and a baseline for strong-field approaches extensions.

Comments
Accepted in J. Phys. B; 14 pages, 6 figures

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Tunneling ionization in static or slowly varying electric fields is a cornerstone of strong-field physics and provides the entry point for semiclassical descriptions of above-threshold ionization and high-harmonic generation. In conventional quantum mechanics, the Perelomov--Popov--Terent'ev (PPT) theory and its Ammosov--Delone--Krainov (ADK) form yield an ionization rate whose defining feature is an exponential dependence governed by an under-barrier (imaginary-time) action. Here we develop an analytical ADK-like tunneling model within \emph{space-fractional} quantum mechanics, where the quadratic kinetic energy is replaced by the Riesz fractional Laplacian of order 1<α≤21<α\le21<α≤2. Working in a static electric field in the length gauge, we derive a closed-form tunneling exponent for a triangular exit barrier. The fractional kinetic operator deforms the conventional Ip3/2I_p^{3/2}Ip3/2​ scaling to Ip1+1/αI_p^{1+1/α}Ip1+1/α​ and introduces a characteristic sin⁡(π/α)\sin(π/α)sin(π/α) factor encoding the complex-phase structure associated with nonlocal dispersion. We position this benchmark relative to prior tunneling studies in fractional quantum mechanics (primarily scattering through model barriers and fractal potentials) and provide a validation protocol for testing the exponent in time-dependent simulations of the fractional Schrödinger equation under a constant field. The result establishes a transparent reference for static-field ionization in nonlocal quantum dynamics and a baseline for strong-field approaches extensions.
Recent attoclock experiments and theoretical studies regarding the strong-field ionization of atoms by few-cycle infrared pulses revealed features that have attracted much attention. Here we investigate tunneling ionization and the dynamics of the electron probability using Bohmian mechanics. We consider a one-dimensional problem to illustrate the underlying mechanisms of the ionization process. It is revealed that in the major part of the below-the-barrier ionization regime, in an intense and short infrared pulse, the electron does not tunnel through the entire barrier, but rather starts already from the classically forbidden region. Moreover, we highlight the correspondence between the probability of locating the electron at a particular initial position and its asymptotic momentum. Bohmian mechanics also provides a natural definition of mean tunneling time and exit position, taking account of the time dependence of the barrier. Finally, we find that the electron can exit the barrier with significant kinetic energy, thereby corroborating the results of a recent study [N. Camus et al., Phys. Rev. Lett. 119, 023201 (2017)].
Time continues to be an intriguing physical property in the modern era. On the one hand, we have the Classical and Relativistic notion of time, where space and time have the same hierarchy, which is essential in describing events in spacetime. On the other hand, in Quantum Mechanics, time appears as a classical parameter, meaning that it does not have an uncertainty relation with its canonical conjugate. In this work, we use a recent proposed spacetime-symmetric formalism~\href{https://doi.org/10.1103/PhysRevA.95.032133}{[Phys.~Rev.~A {\bf 95}, 032133 (2017)]} that tries to solve the unbalance in nonrelativistic Quantum Mechanics by extending the usual Hilbert space. The time parameter ttt and the position operator X^\hat{X}X^ in one subspace, and the position parameter xxx and time operator T\mathbb{T}T in the other subspace. Time as an operator is better suitable for describing tunnelling processes. We then solve the novel 1/21/21/2-fractional integrodifferential equation for a particle subjected to strong and weak potential limits and obtain an analytical expression for the tunnelling time through a rectangular barrier. We compare to previous works, obtaining pure imaginary times for energies below the barrier and a fast-decaying imaginary part for energies above the barrier, indicating the anti-hermiticity of the time operator for tunnelling times. We also show that the expected time of arrival in the tunnelling problem has the form of an energy average of the classical times of arrival plus a quantum contribution.
Abstract: Quantum tunneling is conventionally described through semiclassical WKB methods and imaginary-time formulations of the Feynman Path Integral, which successfully reproduce transmission probabilities but leave the local kinematic structure of the barrier transition largely implicit. In this work, we introduce a finite-rate temporal integration framework in which localized quantum states evolve through successive stochastic re-integrations over a characteristic interval . Within this picture, a macroscopic potential barrier acts as an open fluctuating electromagnetic environment rather than a rigid static boundary. As a localized state partially penetrates the barrier, transient geometric interlocking suppresses forward integration and prolongs the effective interaction window. The under-barrier configuration is modeled not as a single coherent leap across the forbidden region, but as a metastable sequence of stochastic local re-integrations continuously driven by environmental fluctuations. Transmission through thick barriers therefore emerges as a rare cumulative process requiring repeated successful geometric alignments across many finite integration intervals, naturally producing exponential suppression with barrier thickness. To formalize this mechanism, the tunneling process is represented as a coupled stochastic escape problem governed by bipartite Langevin dynamics and an associated Fokker–Planck description. The transition probability acquires a bilinear structure arising from simultaneous compatibility conditions between particle-side and environment-side fluctuations. In the self-consistent limit, this naturally produces the quadratic probability weighting characteristic of the Born measure, while remaining compatible with normalized Hilbert-space amplitudes. Within this framework, the Euclidean-time contribution appearing in standard tunneling theory admits a local kinematic interpretation as the extended stochastic integration interval required for compatible transition geometries to accumulate across the barrier. The formalism further predicts enhanced sensitivity of tunneling dynamics to high-frequency external probing, potentially relevant to attoclock tunneling-delay experiments and strong-field manifestations of the Quantum Zeno effect.
Tunnel-ionization is investigated in the framework of relativistic quantum mechanics. \nFor an arbitrary constant electromagnetic field a gauge invariant energy \noperator is introduced in order to identify the classically forbidden region for \ntunnel-ionization. Furthermore, relativistic features of tunnel-ionization are explored. \nA one-dimensional intuitive picture predicts that the ionized electron wave \npacket in the relativistic regime experiences a momentum shift along the laser’s \npropagation direction. This is shown to be consistent with the well-known strong \nfield approximation. Furthermore, spin dynamics in tunnel-ionization process \nis discussed in the standard as well as in the dressed strong field approximation. \nNext, the tunneling time delay is investigated for tunnel-ionization by extending \nthe definition of the Wigner time delay. Later, this concept is redefined in terms of \nthe phase of the fixed energy propagator. The developed formalism is applied to \nthe deep-tunneling and the near-threshold-tunneling regimes. It is shown that in \nthe latter case signatures of the tunneling time delay can be measurable at remote \ndistance. Finally, the path-dependent formulation of gauge theory is discussed. It \nis demonstrated that this equivalent formulation of gauge theory leads to a canonical \ngauge fixing, in which the Feynman path integral becomes more intuitive and \nthe calculation of the quasiclassical propagator is considerably simplified
This educational technical note derives the leading semiclassical tunneling exponent for a one-dimensional particle in a static electrostatic potential from the local Dirac dispersion relation, and shows how the Schrödinger WKB result follows in the low-energy limit. It also introduces a hypothetical parameter lambda multiplying the quadratic relativistic term and compares the corresponding exponents for a defined rectangular barrier. The standard Dirac-WKB derivation reproduces established relativistic quantum mechanics; it is not presented as a new physical law. The lambda modification is exploratory and has no independent theoretical derivation or experimental support in this note. The numerical comparison is a sensitivity calculation for an illustrative 10 fm rectangular barrier with constant Delta = 0.1 MeV and mu*c^2 = 1118 MeV. It is not a realistic D-T interaction model or a prediction of a fusion reaction rate. The note does not claim cold fusion, anomalous fusion enhancement, or reactor-relevant performance. A one-particle Dirac equation does not describe the complete D-T nuclear collision, which involves composite nuclei, strong-interaction channels, spin, and plasma/environment effects. The cited 2026 D-D metallic-hydride study concerns ion-beam and electrochemical loading conditions and does not validate the hypothetical lambda model or establish self-sustaining fusion. AI assistance: ChatGPT assisted with literature triage, numerical calculations, equation review, and drafting. Chaman Prakash Kanth is responsible for the scientific assumptions, calculations, manuscript, and metadata.
We investigate the tunneling time of a wave packet propagating through a non-Hermitian potential Vr − iVi in space-fractional quantum mechanics. By applying the stationary phase method, we derive a closed-form expression for the tunneling time for this system. This study presents the first investigation of tunneling time at the interplay of non-Hermitian quantum mechanics and space-fractional quantum mechanics. The variation in tunneling time as the system transitions from a real to a complex potential is analyzed. We demonstrate that the tunneling time exhibits a dependence on the barrier width d in the limit d → ∞, showing the absence of the Hartman effect. A particularly striking feature of our findings is the potential manifestation of the Hartman effect for a specific combination of the absorption component Vi and the Levy index α. This behavior arises from the fact that the presence of the absorption component Vi leads to a monotonic increase in tunneling time with barrier thickness, whereas the Levy index α reduces the tunneling time. The interplay of these contrasting influences facilitates the emergence of the Hartman effect under a specific combination of Vi and the fractional parameter α.