Rapid Cooling Techniques Introduced to Advance Quantum Nanotechnology

April 27, 2020 by Luke James

A team of researchers led by physicists at the Technische Univeritat Kaiserslautem (TUK) in Germany and the University of Vienna in Australia have reportedly generated the Bose-Einstein condensate (BEC) through a sudden change in temperature.

Currently, BECs are formed by decreasing temperature to absolute zero or by injecting a large number of particles at room temperature into a small space.

In contrast, the teams’ process involves slowly heating up the quasi-particles called magnons and then rapidly cooling them down to room temperature. In this process, the magnons represent the quanta of magnetic excitations of a solid body. 


A Simpler and More Accessible Process

This new process described by the teams’ research, which was published in the journal Nature Nanotechnology on April 20, is much simpler. It is not technically complex like the current process and only requires a heating source together with a tiny magnetic nanostructure. 

This means that it will, in theory, be accessible to a greater number of research teams worldwide as specialist machinery and in-depth know-how are not required. 

"Our recent progress in the miniaturization of magnonic structures to nanoscopic scale allowed us to address BEC from completely different perspective, [sic]" said Professor Andrii Chumak from the University of Vienna.


A diagram of the rapid cooling process from magnon gas to magnon BEC.

(From left to right) Magnon gas particles bouncing around inside a magnetic nanostructure. When rapidly cooled, they spontaneously jump into the same state, forming a Bose-Einstein condensate (BEC). Image credited to Dr. Andrii Chumak, Technische Universität Kaiserslautern/Universität Wien

The Temperature-Manipulation of Nanostructures 

The process involves slowly heating the nanostructure up to 200 degrees Celsius to generate photons, which in turn generate magnons at the same temperature. The heating source is then shut off and the nanostructure rapidly cools down to room temperature in a nanosecond. When this happens, the photons escape to the substrate but the magnons remain as they are too slow to react. 

When the photons escape, the magnons need to reduce energy to stay in equilibrium. Since they cannot decrease the number of particles as they are too slow to escape the nanostructure, they jump down to the same low energy level instead. By spontaneously occupying the same energy level, the magnons form a BEC. 


An Unexpected Result

The team made their discovery by accident, originally setting out to study a different aspect of nanocircuits. "At first we thought something was really wrong with our experiment or data analysis," the paper’s lead author, Michael Schneider, said. To confirm the presence of BEC, the team tweaked some experimental parameters and used spectroscopy techniques. 

Professor Burkard Hillebrands from TUK said that although “many researchers” are currently studying the different types of BECs, their new approach “should work for all systems,” and added that revealing information about magnons and their behavior in a form of macroscopic quantum state at room temperature “could have bearing on the quest to develop computers using magnons as data carriers.”