PM: Electron and Positron Magnetic Moments from a Quantum Cyclotron

In this project, graduate students will develop apparatus and deploy quantum methods that are capable of extraordinary precision. The unusual sensitivity should allow detection of one-quantum transitions of a single elementary particle. Extremely small motions of a single charge will produce tiny electrical currents that will be detected using instruments cooled to temperatures near to absolute zero.

The faint noise from the thermal motion of the electrons in the detector will be greatly suppressed with a new suite of quantum methods. The quantum state of the particle suspended on the apparatus will be deduced from the rate at which the trapped electron or positron jumps between alternate quantum states. The new apparatus and quantum methods will make it possible to test the most precise prediction of our most fundamental mathematical description of physical reality, the so-called Standard Model of Particle Physics (SM).

A great mystery of modern physics is that this SM description works extremely well in most cases, even though it is not consistent with basic features of our universe. A resolution of this fundamental mystery would be extremely important, given that a change to our fundamental paradigm for physical reality would almost certainly lead to new science and technology.

Furthermore, a fundamental constant that is essential to the system of units used internationally for science and commerce will be measured more accurately than ever before.

At the heart of the new detection methods are “quantum circumvention” methods for measuring particle oscillation frequencies. These will be used with quantum jump spectroscopy that employs quantum nondemolition detection of occupied quantum states. The new methods will reduce the detection backaction to the minimal intrinsic value to that from the quantum zero-point motion of particle oscillations.

The immediate goal for this grant period is to determine the electron and positron magnetic moments to an unprecedented accuracy of 4 parts in 10^14. This will be the most precise measurement ever made of an elementary particle, and it will make is possible to test the most precise prediction of the SM to this unusual precision, a test that is 10 times more stringent than is currently possible.

The comparison of the electron and positron magnetic moments at this extraordinary precision will test lepton CPT invariance, the most fundamental symmetry invariance of the SM more stringently by a factor that could be as large as 200. The measurements will also prepare the way for more accurate measurements of the muon magnetic moment.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.