Bose Einstein Condensate: Producing a Quantum Material
'At this temperature each individual particle behaves more like a wave'
Heather Dunmall | 13 June 2016

We are told throughout secondary education that there are three states of matter. For those reading this with at least a passing interest in science, this might be upped to four with the addition of plasma, however, in reality there are many, many other states. The four common ones: solid, liquid, gas and the aforementioned plasma, are found within ‘real’ conditions, in that they are found to naturally occur. However, exotic states can arise in synthesised, extreme environments. One of these states is Bose Einstein Condensate (BEC).

In 1924, the theory of BEC was first hypothesised by Satyendra Nath Bose and Albert Einstein, however it took until the 1990s for it to be proven by experiment, due to the very low temperatures needed. The image above shows the velocity-distribution data measured as Rubidium forms a condensate, with the data to the left showing the fully formed BEC. When a dilute gas is cooled to temperatures a nanokelvin above absolute zero, it starts to behave in weird and wonderful ways, characterised by the theories present in quantum mechanics. Matter is generally thought to be made up of particles. However, at this temperature each individual particle behaves more like a wave.

Cooling decreases the amount a particle vibrates, and so its momentum, which increases the De Broglie wavelength (defined as Planck’s constant over the momentum of the particle). When the wavelength is long enough that overlap starts to occur, the matter coalesces into  a single condensate. Here all the wavelengths are coherent and oscillate together, occupying the same quantum wave function: this is Bose Einstein Condensate. The amazing thing about BEC is that it has been created in large enough amounts to be seen under a microscope, providing the possibility for real-world applications. It is closely related to superfluidity and superconductivity and, no doubt, the research currently going into BEC will provide stepping stones for further developments in these fields.

Due to the fact BEC has been produced almost macroscopically, it can be used to research into quantum theories which normally only affect matter too small to be observed. This has been exploited by scientists from the University of Tokyo and RIKEN, who were able to prove with BEC a theory called quantum mass acquisition. Put simply, this theory states that minute quantum fluctuations allow the generally massless quasi-Nambu-Goldstone boson to gain mass. This change in an elementary particle seems foreign, and only recently has been proven experimentally using BEC.

Quantum physics is so alien to our school-based science education, due to its seemingly extrinsic application to our everyday lives, and many of the theories being purely hypothetical; it often seems that it will always be missing from the general public’s basic science knowledge. However, the potential for Bose Einstein Condensate to have an impact on our everyday lives, from Maglev’s levitating trains, to more efficient energy transfer, gives hope for change. For such a recently proven theory, BEC has a lot to offer.

 

Image sourced under Creative Commons License.

James Routledge 2016