Scientists Have Discovered “Immortal” Quasiparticles

The menagerie of the quantum world is full of intriguing beasties. It has particles that are also waves, quantum carriers of forces, and phenomena that behave like particles but aren’t. Known as quasiparticles, researchers have now discovered a truly peculiar type: an immortal one.

One of the laws of nature is that decay is unavoidable. Things breakdown all the time, including the fact that we age and die. In the quantum world, some particles are extremely short-lived, while others take eons to decay, but quasiparticles are always on the "live fast, die young" side of things. As reported in Nature Physics, however, this does not seem to be the case for certain quasiparticles.

The team conducted sophisticated simulations of quasiparticles and witnessed a curious phenomenon. If strong interactions create the quasiparticles, then it will behave a bit like a mythological phoenix. It will decay, but from that same decay, it will form back again. These quasiparticles never seem to be fully gone.

“The result of the elaborate simulation: admittedly, quasiparticles do decay, however new, identical particle entities emerge from the debris,” lead author Ruben Verresen, from the Max-Planck-Institute for the Physics of Complex Systems, said in a statement. “If this decay proceeds very quickly, an inverse reaction will occur after a certain time and the debris will converge again. This process can recur endlessly and a sustained oscillation between decay and rebirth emerges.”

Despite the peculiar nature of the “immortal” quasiparticles, they do not violate any known law of physics, especially not the second law of thermodynamics. The entropy of the quasiparticles stays the same and that’s why they don’t truly decay.

The team applied the idea from the simulation stage to experimental quasiparticle phenomena. For example, the peculiar material Ba₃CoSb₂O₉  has extremely stable magnetic properties thanks to a quasiparticle known as a magnon. When helium is cooled to almost absolute zero, it turns into a superfluid that flows with no viscosity and cannot creep along the side of any open container it is placed in and escape. Its behavior is described by the roton quasiparticle. The team behind the study thinks that these quasiparticles are “immortal”.

While the research is currently purely theoretical, knowing these quasiparticles don’t decay might become useful in fields such as quantum computing.