A quasiparticle can be thought of as a ‘pseudo’ article. It’s not an actual particle because it isn’t always present. But, it can’t be considered imaginary either because sometimes it’s just there, though always in a solid material only, never in a liquid or gas. The challenge is in determining when to look for it and how to prove its presence because its formation happens too fast to be observed. Plus, we’re talking about tiny particles, which make them even harder to see.
A couple of months ago, researchers belonging to the University of Innsbruck in Austria published a paper in the journal Science claiming that they witnessed the formation of quasiparticles as it was happening. In other words, they were able to see the quasiparticles as they were being formed. It was considered a major scientific breakthrough because they were the first ones to observe the event in real time — something that many researchers have been trying to achieve for a number of decades.
The question is: what is so important about this event? Well, it has to do with what quasiparticles are. Emerging only in solid matter where electrons and protons are constantly pulling and pushing against each other, quasiparticles do not interact with other particles. In a way, they are like an alternate version of the particles they emerge from. For example, an ‘electron quasiparticle’ behaves like an electron, but it behaves in a way that makes it seem like it has a different mass, so its movement is different from a ‘true’ electron.
Rudolf Grimm, lead author of the research, likens a quasiparticle to a ‘skier on a powder day.’ He says, “The skier is surrounded by a cloud of snow crystals. Together they form a system that has different properties than the skier without the cloud.”
The quasiparticle formation process lasts for only attoseconds. To picture what that’s like, just imagine how fast a split second is. An attosecond is way faster, specifically, one-quintillionth of a second. This blazing speed is what’s making it almost impossible for the process to be observed.
Thankfully, the research team found a way to slow down the process just enough for observation to become doable. In a vacuum chamber, they made use of laser trapping techniques to create super cold quantum gas composed of potassium atoms in the center, surrounded by lithium atoms. Afterwards, they used a magnetic field to alter the normal interaction of the particles, until they were able to create a ‘Fermi polaron’ — a quasiparticle composed of potassium atoms enclosed in a cloud of lithium. The best part? The formation of polarons happened a little slower — a few microseconds instead of attoseconds — so they were able to see it as it was happening.
Observing quasiparticles is only the beginning. The next goal is to find a way to measure the quasiparticles. With this information, it will then become possible to figure out how to develop quantum processors that will lay the groundwork for the ultra-fast electronics we are envisioning for the future.