Critical Spin Dressing Magnetic Field Metrology

The neutron electric dipole moment (nEDM) experiment at the Spallation Neutron Source (SNS) will measure the nEDM via interactions with ³He. Ultimate sensitivity will be reached in that apparatus by using the critical spin dressing technique. Critical spin dressing is the application of an off-resonant oscillatory field that dresses the neutron and ³He spins to have the same effective Larmor precession. Advanced critical spin dressing techniques are in development that can provide high sensitivity measurements of magnetic field gradients with a large dynamic range. Additionally, this measurement technique will distinguish between gradients responsible for limiting the coherence time versus gradients that generate the geometric phase, a linear-in-E frequency shift. A research program has been proposed to develop these techniques at the systematic and operational studies apparatus in the PULSTAR reactor at NCSU.