For the first time, Researchers from Amherst College and Aalto University have carried out experimental observations of the dynamics of isolated monopoles that exist in quantum matter.
The result of the new research was astonishing—the quantum monopole was found to decay into another analogue of the magnetic monopole. The acquired fundamental knowledge on the monopole dynamics can assist in the future to build even closer analogues of the magnetic monopoles.
In contrast to common magnets, magnetic monopoles are elementary particles that have only a north magnetic pole or a south magnetic pole, and not both. Although they were earlier predicted to exist theoretically, there are no credible experimental observations. Hence Physicists have been constantly working to find analogue objects.
In 2014, we experimentally realized a Dirac monopole, that is, Paul Dirac’s 80-year-old theory where he originally considered charged quantum particles interacting with a magnetic monopole.
Professor David Hall, Amherst College, USA
“And in 2015, we created real quantum monopoles,” further added Dr Mikko Möttönen at the Aalto University.
Whereas the Dirac monopole experiment simulates the motion of a charged particle in the vicinity of a monopolar field, the quantum monopole has a point-like structure in its own field resembling that of the magnetic monopole particle itself.
From one quantum monopole to another in less than a second
At present, the monopole collaboration headed by David Hall and Mikko Möttönen has observed the way in which one such distinctive magnetic monopole analogue spontaneously transforms into another in less than one second.
Sounds easy but we actually had to improve the apparatus to make it happen.
Tuomas Ollikainen, First Author of the new study
The Researchers started the experiment by cooling an exceptionally dilute gas of rubidium atoms to near absolute zero—a temperature at which the gas forms a Bose–Einstein condensate. Then, they set the system to be in a non-magnetized state and ramped an external magnetic-field zero point into the condensate to form an isolated quantum monopole. Next, they maintained the zero point and waited for the system to slowly magnetize along the spatially changing magnetic field. The resulting destruction of the quantum monopole is the formation of a Dirac monopole.
I was jumping in the air when I saw for the first time that we get a Dirac monopole from the decay. This discovery nicely ties together the monopoles we have been producing over the years.
Dr Mikko Möttönen, Aalto University
Beyond Nobel physics
The quantum monopole is a commonly known topological point defect, or a single point in space enclosed by a structure existing in the non-magnetized state of the condensate that cannot be eliminated through continuous reshaping. The Nobel Prize in Physics for the year 2016 was related to such structures and was awarded in part for observations of topological phase transitions caused by quantum whirlpools, or vortices.
“Vortex lines have been studied experimentally in superfluids for decades; monopoles, on the other hand, have been studied experimentally for just a few years,” says Professor Hall.
Despite the fact that the quantum monopole is protected by its own topology, it can be disintegrated since the whole phase of matter transitions from being non-magnetized to being magnetized.
“No matter how robust an ice sculpture you make, it all flows down the drain when the ice melts,” stated Mr Ollikainen.
“For the first time, we observed spontaneously appearing Dirac monopoles and the related vortex lines,” stated Dr Möttönen.