Levitated Matter

Levitated particles in air and plasma offer a boundary-free platform for studying rapid many-body dynamics without hard, frictional walls. Acoustic and dusty-plasma systems naturally exhibit non-reciprocal and non-pairwise interactions that are central to active-matter phenomena. Using high-speed cameras and 2D/3D tracking, we capture the dynamics and infer interparticle forces with single-particle resolution.

Dusty Plasma

A plasma is a ionized gas where free electrons and ions are constantly bumping into each other. The plasma state of matter makes up over 99% of the visible universe. When dust particles and grains are introduced into a plasma, the particles will becomed charged and interact through  electrostatic and hydrodynamic forces. For a dense system of particles in a weakly-ionized plasma, the electrostatic force between the particles is dominant, so that the particles can form crystalline structures: a model "playground" for studying lattice dynamics in condensed matter.  ​In our lab we are using dusty plasmas to create highly dynamic, many particle systems. Our setup involves a confined dusty plasma illuminated by a sheet of laser light. The video above showcases the intermittent dynamics that can occur in large, crystalline systems. The video below highlights our 3D tracking method for small collections of dust particles. Here the particle color represents it's position in the vertical (out of plane) direction. Using this imaging technique, we are currently using machine learning methods to infer the complex forces that drive dusty plasma systems. 
https://www.youtube.com/watch?v=lBv-GW0m6LM

Relevant Publications:
Physics-tailored machine learning reveals unexpected physics in dusty plasmas
​3D tracking of particles in a dusty plasma by laser sheet tomography
​Extracting Forces from Noisy Dynamics in Dusty Plasmas
The origin of large amplitude oscillations of dust particles in a plasma sheath
Intermittent "turbulence" in a many-body system
​Emergent Bistability and switching in a nonequilibrium crystal

Acoustic Levitation

Left: We identify particles in a 2D dynamical raft using a customized watershed method combined with linking algorithms. In the left video, tracked particles are highlighted with green circles. We can select any fully tracked particle to visualize its trajectory In the right video, the chosen particle is highlighted with a red circle and its path is shown over time. Middle: We can also identify particle pairs within the system. The video shows the dynamics of one such identified pair. Right: From the tracked particle pairs, we extract rotational information, such as the change in their relative orientation over time. The video illustrates one particle pair along with the evolution of its rotation angle. 

We used a piezoelectric resonator with a glass plate to generate a standing wave that traps micron-scale particles. At the resonance frequency, the particles assemble into a two-dimensional (2D) raft. When the driving frequency is increased beyond resonance, the particles become more dynamic and transition into a three-dimensional (3D) “scattering state,” where they move freely like a gas. If the frequency is tuned only slightly above resonance, the particles remain more mobile than in a static crystal but still interact strongly, allowing them to exchange positions. We refer to this regime as the “intermediate state.” In this state, particles can collide and stick together via van der Waals forces, forming intriguing structures such as polymer-like chains.

Relevant Publications:
The lifetime of charged dust in the atmosphere