No touching allowed! How levitation is unlocking the secrets of charged matter

Imagine studying something so sensitive, so finicky, that you can't even touch your samples without altering them. This is the challenge we face when working with electrically charged granular matter or aerosols, where every contact can potentially transfer or siphon the very charges we aim to study. In my lab, we are pioneering techniques that allow us to investigate the physics of such charged matter without ever having to touch our samples. The secret? Levitation. First I will describe our experiments using acoustic levitation to measure the absolute charge of macroscopic (500 micron) granular matter. Using high-resolution, high-speed imaging, we achieve measurement precision down to +-500 elementary charges on particles large enough to be seen with the naked eye. I'll show how we can also measure a particle's electric polarizability and, taking advantage of conductive particles, even control charge to be whatever we want. Finally, I'll discuss how other forms of levitation beyond acoustics allow us to probe particles at the scale of a single aerosol (1 micron) particle, measuring charge with sub-electron resolution and in real time. Our techniques are unlocking secrets about why things get charged in the first place, with relevance to natural phenomena ranging from dust storm electrificationto lightning to planet formation.