Larmor precession and the traversal time for tunneling

TLDR

Larmor precession has been proposed as a clock to measure how long a particle spends traversing a barrier, with a magnetic field confined to the barrier and incident spins polarized perpendicular to it, while dwell, traversal, and reflection times characterize the average, transmitted, and reflected interaction intervals. The study interprets the experiment by comparing Larmor precession measurements with traversal times obtained from transmission through a time‑modulated barrier. The extent of Larmor precession during transmission is used to measure traversal time, and the experiment compares this with a time‑modulated barrier approach. The analysis shows that tunneling through an opaque barrier induces a spin component parallel to the field, a phenomenon also exploited for electron and neutron polarization, and yields three distinct characteristic times for particle–barrier interaction.

Abstract

Baz' and Rybachenko have proposed the use of the Larmor precession as a clock to measure the time it takes a particle to traverse a barrier. An applied magnetic field is confined to the barrier. The spin of the incident particles is polarized perpendicular to this field. The extent of the Larmor precession occurring during transmission is used as a measurement of the time spent traversing the barrier. However, the particles tunneling through an opaque barrier also acquire a spin component parallel to the field since particles with spin parallel to the field have a higher transmission probability than particles with spin antiparallel to the field. Similar effects are actually used to polarize electrons and neutrons. An interpretation of this experiment compares the results with an approach which determines the traversal time by studying transmission of particles through a time-modulated barrier. This leads to three characteristic times describing the interaction of particles with a barrier. A dwell time measures the average time interval during which a particle interacts with the barrier whether it is reflected or transmitted at the end of its stay, a traversal time measures the time interval during which a particle interacts with the barrier if it is finally transmitted, and a reflection time measures the interaction time of a reflected particle.