A fundamental limit to the efficiency of spin-exchange optical pumping of 3He nuclei

TL;DR

This paper identifies a fundamental physical limit to the maximum achievable polarization of 3He nuclei via spin-exchange optical pumping, determined by anisotropic hyperfine interactions, with implications for optimizing hyperpolarization techniques.

Contribution

It provides ab initio calculations showing the hyperfine interaction limits 3He polarization and compares spin exchange rates for Ag and K, suggesting new experimental approaches.

Findings

Maximum 3He polarization limited by anisotropic hyperfine interaction.

Ag-3He collisions exhibit faster spin exchange than K-3He.

Trap loss measurements can probe anisotropic interactions.

Abstract

We establish the existence of a fundamental limit to the efficiency of spin-exchange optical pumping of 3He nuclei by collisions with spin-polarized alkali-metal atoms. Using accurate ab initio calculations of molecular interactions and scattering properties, we show that the maximum 3He spin polarization that can be achieved in spin-exchange collisions with potassium (39K) and silver (107Ag) atoms is limited by the anisotropic hyperfine interaction. We find that spin exchange in Ag-He collisions occurs much faster than in K-He collisions, suggesting the possibility of using Ag in spin-exchange optical pumping experiments to increase the production rate of hyperpolarized 3He. Our analysis indicates that measurements of trap loss rates of 2S atoms in the presence of cold 3He gas may be used to probe anisotropic spin-exchange interactions in atom-He collisions.