Ramsey Prize Talk: New Generation Measurements of the Electron's Electric and Magnetic Dipole Moments

The ACME motivations and methods were summarized by Doyle and DeMille. Also summarized was the 100 times improved sensitivity to an electron electric dipole moment (EDM) that came from our ACME I and ACME II measurements, and a very recent 2.4 times improvement [3]. Given the importance of finding more of the CP violation that seems needed to explain the matter-antimatter imbalance in the universe (that the Standard Model (SM) cannot explain), and to provide some of the most stringent limits on "beyond the Standard Model” (BSM) physics, we have launched a new generation ACME III measurement. Our goal is to either discover the electron EDM or set a new electron EDM limit that is smaller by a factor of 20. A new apparatus increases the molecule flux by facilitating frequent ablation target changes, uses an electrostatic lens to capture more molecules from a cold ablation source, allows a 5 times longer coherence time, and uses detectors with a higher quantum efficiency. A two-layer, actively-shielded coil just inside of 3 layers of mu-metal shielding provides a magnetic field over a 1 m precession length with negligible shield magnetization, producing a field reversable to better than 1 nT (10 micro-Gauss) to provide a needed reduction in systematic error.

Meanwhile, in a separate measurement using entirely different methods, special relativity and quantum-limited detection are the new ideas that will propel a new generation measurement of the electron’s other moment -- its magnetic moment -- and also that of the positron. The two spin energy states and the two lowest cyclotron states of one electron or positron trapped at crogenic temperatures form qubits whose state can be read out using a quantum-limited SQUID detector via a QND coupling provided by special relativity. The first goal is measuring the electron magnetic moment [4] 10 times more accurately, to make the morst precise test of the most precise prediction of the SM, and to set stringent BSM limits. The second goal is measuring the positron magnetic moment [5] 200 times more accurately, to make the most precise lepton test of the SM’s fundamental CPT invariance. A third goal is to tp provide greater sensitivity to dark photons than the 75 times improved sensitity that we recently demonstrated [6].