Work

Low-noise environment for probing fundamental symmetries

Year: 2025

Type: article

Abstract: We present the design and characterization of a low-noise environment for measuring the electron’s electric dipole moment (EDM) with a beam of molecules. To minimize magnetic Johnson noise from metals, the design features ceramic electric field plates housed in a glass vacuum chamber. To suppress external magnetic noise the apparatus is enclosed within a cylindrical four-layer mu-metal shield with a shielding factor exceeding 106 in one radial direction and 105 in the other. Finite element modelling shows that the difference between these shielding factors is due to imperfect joints between sections of mu-metal. Using atomic magnetometers to monitor the magnetic field inside the shield, we measure noise below 40 fT Hz − 1 at 1 Hz and above, rising to 500 fT Hz − 1 at 0.1 Hz. Analytical and numerical studies show that residual magnetic Johnson noise contributes approximately 13 fT Hz − 1 . The background magnetic field averaged along the beamline is maintained below 3 pT, with typical gradients of a few nT m−1. An electric field of 20 kV cm−1 is applied without discharges and with leakage currents below 1 nA. Each magnetometer measures the magnetic field correlated with the direction of the applied electric field with a precision of 0.11 fT in 104 h of data. These results demonstrate that the apparatus is suitable for measuring the electron EDM with precision at the 10−31 e cm level. The design principles and characterization techniques presented here are broadly applicable to precision measurements probing fundamental symmetries in molecules, atoms, and neutrons.

Source: New Journal of Physics

DOI: 10.1088/1367-2630/ae0ea7