Physicists witness the bizarre birth of a ‘quasiparticle’

Physicists exploring the quantum world watched the birth of a quasiparticle, shedding light on the strange behavior of these bizarre  “fake particles.” 

Quasiparticles have been an enigmatic entity in the world of physics since they were first introduced as a concept in the 1930s. They’re strange disturbances in physical systems that aren’t particles, but rather behave like particles. In a new study, physicists were able to observe a strange type of quasiparticle being born, which allowed them to explore the behavior of these odd physical systems.

“Quasiparticles are extremely interesting, since they may consist of countless particles and their excitations,” Magnus G. Skou, a physicist at Aarhus University in Denmark who worked on this study, told

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In this new study, the team essentially created quasiparticles. To do this, they used an ultra-cold gas of atoms. The researchers prepared a “coherent superposition state” of atoms — atoms existing in two states at the same time — in a Bose-Einstein condensate, which is a group of atoms cooled to almost absolute zero that clumped together, acting as one atom. Using ultrafast radio-frequency radiation, they created impurities in the atoms, allowing them to study quantum impurities. 

“Our experiments were performed using a medium of atoms cooled down to a stunningly low temperature of only a billionth degree above absolute zero, which is far below the temperature of outer space,” Skou said.

They watched these quantum superpositions and saw them ultimately evolve into a certain type of quasiparticle known as a polaronic quasiparticle, which is a transient mash-up of electrons and atoms that exists for just trillionths of a second. These types of quasiparticles can allow scientists to study how electrons and atoms interact in a solid material. 

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The polaronic quasiparticle, or polaron, they watched come to be was a particular variety known as the Bose polaron. Bose polarons are quasiparticles that are made of certain types of atoms immersed in a Bose-Einstein condensate. This study marked the first time that researchers have directly observed the “birth” of a Bose polaron, as these observations are difficult to make because these processes happen so fast. 

By watching the birth of these quasiparticles and studying their quantum impurities, “we found that the impurities began to dynamically interact with the atoms of the medium, and we measured this evolution,” Skou said. 

“Our study is a big step forward in understanding Bose polarons, their non-equilibrium dynamics and how they are formed,” Skou said. “These quantum phenomena are exceedingly fascinating by themselves, but they are furthermore conjectured to be key elements in exotic technologies such as organic semiconductors and superconductors.”

Email Chelsea Gohd at [email protected] or follow her on Twitter @chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.


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