Physicists make the most accurate measurements yet of the magnetic moments of an electron

(a) Cryogenic system supports a 50 mK electron trap on a 4.2 K solenoid to provide a very stable B. (b) Silver electrodes of a cylindrical Penning trap. (c) Quantum spin and cyclotron energy levels used for measurement. Credit: Physical review letters (2023). DOI: 10.1103/PhysRevLett.130.071801

A combined team of physicists from Harvard University and Northwestern University has found the most precise value yet for the magnetic moment of an electron. In their paper published in the journal Physical review lettersthe group describes the methods they used to measure the properties of an electron and the implications of the new precision.

The magnetic moment of an electron, also known as the electron magnetic dipole moment, is a result of its electrical and spin properties. Of all the elemental properties that have been studied, it is the one that has been most accurately measured, and also the most accurately verified.

Measuring the magnetic moment of an electron to ever higher standards of accuracy is important because physicists believe that at some point such measurements will help complete the Standard Model of physics. In this new effort, the research team has measured the magnetic moment to a precision twice that of another effort – the last best effort was 14 years ago.

Physicists use the magnetic moment of particles such as electrons to test the Standard Model by studying interactions between them and virtual particles that occur inside a vacuum chamber. Such a study involves measuring the effect of collisions on both the magnetic moment and its g-factor and then comparing the results with what is described by the standard model.

The work involved suspending a single electron in a Penning trap with a magnetic field held constant at 5 T. The chamber was then cooled to almost absolute zero. Measurements were taken of what the team describes as “quantum jumps” of the electrons between energy levels. Then, using a magnetic field gradient, they were able to perform quantum non-demolition detection – a technique for measuring quantum jumps without changing the quantum state, reducing the uncertainty of the measurements of the magnetic moment. The end result was the measurement of the magnetic moment to a degree of precision never before achieved – 0.13 parts per trillion.

The new measurements are expected to influence work on future tests of the standard model.

More information:
X. Fan et al, Measurement of Electron Magnetic Moment, Physical review letters (2023). DOI: 10.1103/PhysRevLett.130.071801

Journal information:
Physical review letters

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