Demonstration of magic dressing of $^3$He

Abstract: A common concern in high-precision neutron electric dipole moment (nEDM) experiments is that of magnetic field stability. For static fields, this problem can be mitigated through the use of a superconducting holding field coil, which when operated in persistent current mode serves to stabilize the magnetic field. However, such a solution is not viable when time-varying magnetic fields are present, as is the case for the spin dressing mode of the proposed nEDMSF (nEDM super-fluid) experiment. This experiment features an oscillating magnetic field to dress the gyromagnetic ratios of $^3$He and neutrons to the same value, a condition known as critical dressing. Fluctuations in the dressing field amplitude have the potential to disrupt this condition. Here, we investigate a modification to spin dressing, termed ``magic dressing,'' which renders the system insensitive to small variations in dressing field amplitude. We further demonstrate the utility of this method for the single spin-species case using a sample of polarized $^3$He. We find a dramatic increase in transverse relaxation time in the presence of magnetic field gradients.