# Continuously observing a dynamically decoupled spin-1 quantum gas

## TL;DR

This paper demonstrates continuous observation of dynamical decoupling in a spin-1 quantum gas, revealing real-time spectral features and a regime decoupled from magnetic fluctuations, with potential applications in sensitive biomagnetic measurements.

## Contribution

It introduces a method for continuous measurement of dynamical decoupling in a spin-1 quantum gas, providing real-time spectral analysis and identifying a regime resilient to magnetic noise.

## Key findings

- Real-time spectral analysis of spin states
- Decoupling from magnetic field fluctuations up to fourth order
- Potential for biomagnetic sensing applications

## Abstract

We continuously observe dynamical decoupling in a spin-1 quantum gas using a weak optical measurement of spin precession. Continuous dynamical decoupling aims to dramatically modify the character and energy spectrum of spin states to render them insensitive to parasitic fluctuations. Continuous observation measures this new spectrum in a single-preparation of the quantum gas. The measured time-series contains seven tones, which spectrogram analysis parses as splittings, coherences, and coupling strengths between the decoupled states in real-time. With this we locate a regime where a transition between two states is decoupled from magnetic field instabilities up to fourth order, complementary to the parallel work at higher fields by Trypogeorgos et al. (arXiv:1706.07876). The decoupled microscale quantum gas offers magnetic sensitivity in a tunable band, persistent over many milliseconds: the length scales, frequencies, and durations relevant to many applications, including sensing biomagnetic phenomena such as neural spike trains.