Low-noise environment for probing fundamental symmetries

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 $10^6$ in one radial direction and $10^5$ 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/$\sqrt{\mathrm{Hz}}$ at 1 Hz and above, rising to 500 fT/$\sqrt{\mathrm{Hz}}$ at 0.1 Hz. Analytical and numerical studies show that residual magnetic Johnson noise contributes approximately 13 fT/$\sqrt{\mathrm{Hz}}$. The background magnetic field averaged along the beamline is maintained below 3 pT, with typical gradients of a few nT/m. An electric field of 20 kV/cm 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 hours 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.

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References in corpus (8)

• Precision Measurement of Time-Reversal Symmetry Violation with Laser-Cooled Polyatomic Molecules
• A low-noise ferrite magnetic shield
• Calculation of Magnetic Field Noise from High-Permeability Magnetic Shields and Conducting Objects with Simple Geometry
• Measuring the stability of fundamental constants with a network of clocks
• Measurement of the Electric Dipole Moment of ${}^{171}$Yb Atoms in an Optical Dipole Trap
• A robust floating nanoammeter
• Pulsed beams as field probes for precision measurement
• Slow molecular beams from a cryogenic buffer gas source

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