High-purity solid parahydrogen

TL;DR

This paper demonstrates a method to produce high-purity solid parahydrogen with orthohydrogen impurities below 1e-6, using a cryogenic catalyst to enhance quantum sensor performance.

Contribution

It introduces a cryogenic catalytic process to produce ultra-pure solid parahydrogen with minimal orthohydrogen and HD impurities.

Findings

Orthohydrogen impurity level < 1e-6 in solid parahydrogen.

Cryogenic catalyst operates effectively down to 8 K.

Isotopic purification reduces HD fraction at low temperatures.

Abstract

Alkali atoms trapped in solid hydrogen matrices have demonstrated ultralong electron spin coherence times, and are promising as quantum sensors. Their spin coherence is limited by magnetic noise from naturally-occurring orthohydrogen molecules in the parahydrogen matrix. In the gas phase, the orthohydrogen component of hydrogen can be converted to parahydrogen by flowing it over a catalyst held at cryogenic temperatures, with lower temperatures giving a lower orthohydrogen fraction. In this work, we use a single cryostat to reduce the orthohydrogen fraction of hydrogen gas and grow a solid matrix from the resulting high-purity parahydrogen. We demonstrate operation of the catalyst down to a temperature of 8 K, and we spectroscopically verify that orthohydrogen impurities in the resulting solid are at a level < 1e-6. We also find that, at sufficiently low temperatures, the cryogenic catalyst provides isotopic purification, reducing the HD fraction.