Identical Spin Rotation Effect and Electron Spin Waves in Quantum Gas of Atomic Hydrogen

TL;DR

This study experimentally investigates electron spin waves in high-density atomic hydrogen gas, revealing the Identical Spin Rotation effect, magnetic confinement of spin modes, and magnon condensation at a critical density, advancing understanding of quantum spin phenomena.

Contribution

The paper demonstrates the observation and control of spin wave modes and magnon condensation in atomic hydrogen gas, highlighting the role of the Identical Spin Rotation effect in a quantum regime.

Findings

Observation of various spin wave modes influenced by magnetic potential

Demonstration of magnetic confinement and manipulation of spin modes

Detection of magnon ground state accumulation and long coherence

Abstract

We present an experimental study of electron spin waves in atomic hydrogen gas compressed to high densities of $\sim 5 \times 10^{18}$ cm$^{-3}$ at temperatures ranging from 0.26 to 0.6 K in strong magnetic field of 4.6 T. Hydrogen gas is in a quantum regime when the thermal de Broglie wavelength is much larger than the s-wave scattering length. In this regime the identical particle effects play major role in atomic collisions and lead to the Identical Spin Rotation effect (ISR). We observed a variety of spin wave modes caused by this effect with strong dependence on the magnetic potential caused by variations of the polarizing magnetic field. We demonstrate confinement of the ISR modes in the magnetic potential and manipulate their properties by changing the spatial profile of magnetic field. We have found that at a high enough density of H gas the magnons accumulate in their ground state in the magnetic trap and exhibit long coherence, which has a profound effect on the electron spin resonance spectra. Such macroscopic accumulation of the ground state occurs at a certain critical density of hydrogen gas, where the chemical potential of the magnons becomes equal to the energy of their ground state in the trapping potential.