Development of a SQUID-based 3He Co-magnetometer Readout for a Neutron Electric Dipole Moment Experiment

TL;DR

This paper presents a design study for a SQUID-based readout system for a helium-3 co-magnetometer, aiming to improve neutron EDM measurements by enhancing magnetic field stability and detection sensitivity.

Contribution

It introduces a novel SQUID readout design tailored for a neutron EDM experiment, addressing challenges of long lead connections and signal detection.

Findings

Designed a SQUID system suitable for long lead connections.

Analyzed the magnetic noise and signal detection efficiency.

Proposed solutions to optimize the helium-3 precession signal readout.

Abstract

A discovery of a permanent electric dipole moment (EDM) of the neutron would provide one of the most important low energy tests of the discrete symmetries beyond the Standard Model of particle physics. A new search of neutron EDM, to be conducted at the spallation neutron source (SNS) at ORNL, is designed to improve the present experimental limit of ~10^-26 e-cm by two orders of magnitude. The experiment is based on the magnetic-resonance technique in which polarized neutrons precess at the Larmor frequency when placed in a static magnetic field; a non-zero EDM would be evident as a difference in precession frequency when a strong external electric field is applied parallel vs. anti-parallel to the magnetic field. In addition to its role as neutron spin-analyzer via the spin-dependent n+3He nuclear capture reaction, polarized helium-3 (which has negligible EDM) will serve as co-magnetometer to correct for drifts in the magnetic field. In one of the two methods that will be built into the apparatus, the helium-3 precession signal is read out by SQUID-based gradiometers. We present a design study of a SQUID system suitable for the neutron EDM apparatus, and discuss using very long leads between the pickup loop and the SQUID.