The field of quantum physics is rife with avenues leading to enticing new realms of exploration, yet one enigmatic phenomenon offers a unique window into a reality where particles exhibit unconventional behavior – known as the mirror effect.
Dubbed the 'Alice ring' in homage to Lewis Carroll's renowned tales of Alice's Adventures in Wonderland, the existence of this phenomenon confirms a hypothesis that has persisted for decades regarding the decay of monopoles. Specifically, it reveals that monopoles decay into a vortex resembling a ring, and as other monopoles pass through its center, they are transformed into their respective opposite magnetic charges.
Published in Nature Communications on August 29, these findings represent the latest advancement in the collaborative efforts of Mikko Möttönen, a professor at Aalto University, and David Hall, a professor at Amherst College.
"Our collaboration achieved the creation of Alice rings in a natural setting for the first time, which was a significant achievement," stated Möttönen.
"This pivotal investigation opens up new avenues for comprehending the behavior of these patterns and their counterparts in particle physics throughout the universe," added Hall.
The longstanding collaboration, known as the Monopole Collaboration, initially established the presence of a quantum analog of the magnetic monopole in 2014, isolated quantum monopoles in 2015, and ultimately observed the transformation of one into the other in 2017.
Monopoles remain an elusive concept in the realm of quantum physics. As the name suggests, monopoles are the singular counterparts to dipoles, which possess a positive charge at their north pole and a negative charge at their south pole. In contrast, a monopole carries either a positive or negative charge exclusively.
While the concept seems straightforward, realizing an actual monopole has proven to be a defining challenge in the field. Here's how the Monopole Collaboration achieved it: by manipulating a gas of rubidium atoms in a non-magnetic state at extremely low temperatures near absolute zero. Under these extreme conditions, they induced a monopole by manipulating the phase of a three-layered magnetic field within the quantum gas.
Laying the Theoretical Groundwork
These quantum monopoles are inherently transient, decaying within a few milliseconds of their creation. It's within this transient nature that the Alice ring phenomenon comes into play.
"Think of the monopole as an egg teetering at the top of a hill," explained Möttönen. "The slightest perturbations can send it tumbling down. Similarly, monopoles are susceptible to disturbances that trigger their transformation into Alice rings."
While monopolies are fleeting, the research team simulated stable Alice rings lasting up to 84 milliseconds – over 20 times longer than the monopole's lifespan. This leads researchers to be optimistic that future investigations will unveil more distinct properties of Alice rings.
"From a distance, the Alice ring appears much like a monopole, but the world takes on a different aspect when viewed through the ring's center," Hall described. "From this perspective, everything seems mirrored, as if the ring were a gateway into a universe of antimatter instead of matter," Möttönen added.
In theory, a monopole passing through the center of an Alice ring would transform into an anti-monopole with an opposite charge. Similarly, the charge of the Alice ring would also change. While this phenomenon has yet to be experimentally observed, Möttönen noted that the topological structure of Alice rings necessitates this behavior.
The experimental work was primarily conducted at Amherst College by Ph.D. candidate Alina Blinova and Hall, while Möttönen and his team were responsible for running parallel simulations. This allowed both teams to corroborate the interpretation of the experimental observations.
"It's truly incredible to have such a significant discovery as the culmination of my PhD work," expressed Blinova.
The simulations conducted at Aalto University were made possible with support from the CSC - IT Center for Science and the Research Council of Finland through its Center of Excellence in Quantum Technology. The experiments in the US received financial support from the National Science Foundation.