A single electron may be slightly squashed, and a new experiment in London will measure its shape with unprecedented precision. This matters because the visible Universe is made almost entirely of matter, yet the known laws of physics barely distinguish matter from antimatter. Some undiscovered force must account for this imbalance, and that force would subtly distort fundamental particles like the electron, giving them an electric dipole moment—a measurable asymmetry. So far, every measurement has found the electron perfectly spherical, meaning any distortion is vanishingly small. The team will trap ytterbium fluoride molecules cooled to 50 microkelvin—a new technological advance that makes the measurement hundreds of times more sensitive than previous attempts. The molecule’s internal electric field, amplified by special relativity, magnifies the electron’s distortion, making it detectable. This is fundamental science with no immediate practical application. But the forces it probes lie far beyond the energy range of the Large Hadron Collider, and the techniques developed—ultracold molecule control and extreme sensitivity to tiny energy shifts—could eventually underpin new quantum sensors or tests of fundamental physics. Past fundamental research on particle shapes and symmetries led directly to technologies like GPS and MRI.
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The visible Universe contains hardly any antimatter, but plenty of matter. The known fundamental forces barely distinguish between matter and antimatter so there must be undiscovered forces that account for this asymmetry. These new forces must influence the shapes of the fundamental particles, making them slightly aspherical. Measuring this distortion - known as the electric dipole - will reveal the existence and nature of the new forces. So far, measurements have detected only spherical particles, showing that their electric dipoles are exceedingly small. We aim to determine the shape of the electron by measuring the tiny interaction energy of the electric dipole with an applied electric field. This energy is enhanced when the electron is bound up in a polar molecule, an effect of special relativity. We will use a gas of ytterbium fluoride molecules, whose enhancement factor is a million, cooled to a temperature of 50 microkelvin. This deep cooling is a new technological advance that will make our measurement hundreds of times more sensitive than previous experiments. We will be sensitive to fundamental forces lying far beyond the energy range of the Large Hadron Collider, but we will not need a particle collider - the experiment will be done in a small laboratory in London. In the first two years, we will design and build the apparatus needed to make the measurement. Then we will optimize each part of the apparatus, and demonstrate that it is sensitive to the shape of the electron at the anticipated level. Finally, we will investigate potential systematic errors in the experiment - effects that might mimic the signature of an electric dipole - and eliminate these errors so that the experiment is perfected.
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