Super narrow peaks in excitation spectrum of alkali spin polarization: non-adiabatic case of spin dynamics

TL;DR

This paper theoretically investigates non-adiabatic spin dynamics in alkali vapors under a strong alternating magnetic field, revealing super narrow peaks in the excitation spectrum due to non-resonant, non-adiabatic effects.

Contribution

It introduces a quantum model explaining super narrow peaks in spin polarization spectra caused by non-adiabatic effects, distinct from traditional resonance phenomena.

Findings

Super narrow peaks observed in the excitation spectrum.

Peaks occur without a constant magnetic field component.

Non-adiabatic dynamics explain the peaks.

Abstract

We theoretically describe the phenomenon of non-adiabatic spin dynamics, which occurs in a gas cell filled by alkali vapor in presence of a strong alternating magnetic field and pump light. Steep increase of the spin polarization occurs if frequency of the magnetic field is equal to the certain value. Although, the observable effect relies on the periodic field that consists of two perpendicular components defined by harmonics with the same amplitudes and different frequencies. Considered spin effect cannot be explained by a resonance, because the own Larmor frequency of spin precession is absent without a constant component of magnetic field. Moreover, there are some clearly visible peaks in the excitation spectrum of spin polarization, and they are super narrow in comparison to relaxation rate. Detailed analysis according to proposed quantum model results in the reasoning of the effect via qualitative properties of non-adiabatic dynamics of atomic spin.