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What Is a Quasiparticle?

A quasiparticle is a collection of quantum characteristics among particles operating in their own, particle-like way.

Unlike fundamental bits of matter like electrons and quarks, quasiparticles aren't members of the standard model. And unlike neutrons, protons, or even atoms and molecules, they aren't independent structures floating about on their own in free space.

 

Similar to fundamental particles, though, quasiparticles have fundamental properties like charge and spin. For instance, an "electron quasiparticle" has the same spin and charge as its electron component, but combined with other quantum influences its mass can be quite different.

Theoretical models have found examples of quasiparticles that are basically immortal. While a form of decay is inevitable, identical particles can rise from the ashes like a phoenix, keeping the cycle going indefinitely.

The history of quasiparticles

The first researcher to describe these 'sort of but not really particles' was the Russian physicist Lev Landau.

While studying the odd superfluid behaviour of liquid helium, Landau made connections with the fluid's activity and a quantum concept known as dressed particles. These are bare particles (such as electrons) combined with characteristics from other excitations in their quantum field, such as photons or interactions with positrons.

Since then, our understanding of quasiparticles as a concept has increased by leaps and bounds. While their formation has been extensively described in theoretical terms, it wasn't until 2016 that scientists were able to measure and observe examples of these ultra-fast, short-lived phenomena in real time.

Quasiparticles could play a big role in understanding superconduction, as well as  the future of some types of quantum computing technology.

Examples of quasiparticles

Polaron: A moving electron that interacts with surrounding atoms in a way that shields its charge with a cloud of polarisation.

Exciton: An electron bound to a 'gap' in charge known as an electron hole.

Majorana fermion: A neutrally charged quasiparticle that's considered a particle and its own antiparticle at the same time.

Phonon: The quantum equivalent of a sound wave, or a vibration through atoms in a neat, crystal arrangement.

 

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