Above potential barrier diffusion

Reflection above the barrier as tunneling in momentum space

Quantum mechanics predicts an exponentially small probability that a particle with energy greater than the height of a potential barrier will nevertheless reflect from the barrier in violation of classical expectations. This process can be regarded as tunneling in momentum space, leading to a simple derivation of the reflection probability.

Experimental evidence for the role of cantori as barriers in a quantum system

We investigate the effect of cantori on momentum diffusion in a quantum system. Ultracold caesium atoms are subjected to a specifically designed periodically pulsed standing wave. A cantorus separates two chaotic regions of the classical phase space. Diffusion through the cantorus is classically predicted. Quantum diffusion is only significant when the classical phase-space area escaping through the cantorus per period greatly exceeds Planck's constant. Experimental data and a quantum analysis confirm that the cantori act as barriers.

双电子双原子核有效哈密顿量与自旋扩散势垒

Two-electron two-nucleus effective Hamiltonian and the spin diffusion barrier

本研究针对动态核极化中的自旋扩散势垒问题，通过Schrieffer-Wolff变换分析双电子双核四自旋系统的二阶跃迁，发现能量守恒的电子-核四自旋翻转过程，经实验拟合验证其相关性，提出需重新考量自旋扩散势垒概念。

Ge thin-films with tantalum diffusion-barriers for use in Nb-based superconductor technology

Germanium thin films are an excellent candidate for use as a low-loss dielectric in superconducting microwave resonators, a low-loss inter-layer metal wiring dielectric, and passivation layers in microwave and Josephson junction devices. In Ge/Nb structures deposited at 400 °C, we observe intermixing over as much as 20 nm. The addition of a 10 nm Ta diffusion barrier layer reduces the superconductor/dielectric intermixing to less than 5 nm and enhances the structural properties of deposited a-Ge layers based on Raman spectroscopy. Additionally, superconducting microwave resonators fabricated a…

Transmission through a non-overlapping well adjacent to a finite barrier

We point out that a non-overlapping well (at negative energies) adjacent to a finite barrier (at positive energies) is a simple potential which is generally missed out while discussing the one-dimensional potentials in the textbooks of quantum mechanics. We show that these systems present interesting situations wherein transmitivity $(T_b(E))$ of a finite barrier can be changed both quantitatively and qualitatively by varying the depth or width of the well or by changing the distance between the well and the barrier. Using delta (thin) well near a delta (thin) barrier we show that the well ind…

Quantum Kramers' equation for energy diffusion and barrier crossing dynamics in the low friction regime

Based on a true phase space probability distribution function and an ensemble averaging procedure we have recently developed [Phys. Rev. E 65, 021109 (2002)] a non-Markovian quantum Kramers' equation to derive the quantum rate coefficient for barrier crossing due to thermal activation and tunneling in the intermediate to strong friction regime. We complement and extend this approach to weak friction regime to derive quantum Kramers' equation in energy space and the rate of decay from a metastable well. The theory is valid for arbitrary temperature and noise correlation. We show that depending …