by Rukhsar Naguman
What is the coldest thing in the world and where can you find it? Our minds often wander to places such as Antarctica where temperatures average around −60 °C. But the answer to our question lies in a physics lab as the 5th state of Matter; Bose-Einstein Condensate.
To understand this 5th state of matter and its bizarre properties, we need to first dive into Particle Physics. The elementary particles are spilt into two groups: Bosons and Fermions. These are essentially the spin classification of the subatomic particles. By spin, I do not mean that these particles literally spin but instead they have an angular momentum which corresponds to their spin value. Bosons are known as “force carriers” and have a spin of an integer value i.e., 0, 1, 2, 3, etc. Fermions on the other hand make up “matter” and have a spin of a half odd-integer value i.e., 1/2, 3/2, 5/2, etc. In a system, Bosons can have the same energy level as each other and as a result can enter the state of Bose-Einstein Condensate.
Particles behave distinctively in varying temperatures. In extremely high temperatures, we have plasma. When cooled down, it is gas. And as we continue to decrease the temperature, we get liquids and eventually solids. But what happens when these boson particles are at extremely low temperatures? Firstly, what is temperature? Temperature is the average kinetic energy of particles in a system. There are different scales to measure temperature such as the Kelvin, Centigrade or Fahrenheit but we will use the Kelvin scale as it is an absolute scale meaning there are no negative values for the temperature, the lowest temperature is 0 Kelvin or Absolute zero. When we measure temperature, what we are ultimately measuring is the motion in the system. So, at absolute zero, all the particles are stationary in the system and there is no kinetic energy. Unfortunately, it is experimentally impossible to reach absolute zero because of the 2nd and 3rd Laws of Thermodynamics. We also face a quantum limitation when trying to reach to 0 Kelvin: The Heinsberg’s Uncertainty Principle of Position and Momentum. This principle states that one cannot accurately measure the position and the momentum of a particle simultaneously. Momentum and Position are conjugate pairs. When you increase the accuracy of your calculations for one variable (Momentum), the accuracy of the calculations for the other variable (Position) drops and vice versa. So, in the quantum world, nothing is ever stationary.
Now the
question remains, what happens to the boson particles when they are close to
absolute zero? In the quantum world, everything possesses a wave-particle
duality behaving both as a wave and a particle. When boson gas is at extremely
low temperatures, it no longer behaves as a particle. Instead, it acts as a
“wave packet” and as we continue to decrease the temperature to near absolute
zero, these wave packets are stretched. If each wave packed is spaced out from
one another, they are distinguishable. But when the temperature become
sufficiently low (close to absolute zero) these wave packets are stretched
further and start to overlap one another (becoming undistinguishable) as most
of the bosons reach the lowest energy level known as the “ground state” forming
a “single collective quantum wave called a Bose-Einstein Condensate.” This is
the 5th state of matter where all the atoms are in unison, behaving
as one entity, called the “Super atom.” This property of behaving as one entity
where all atoms are essentially coherent to one another can be used to build
“atom lasers” for atomic-scale lithography or to measure and detect
gravitational fields. Superconductors can also be made from this state of
matter as there is no resistance.
Bose-Einstein Condensate was first theorised around 90 years ago by Satyendra Nath Bose and Albert Einstein. “Expanding on Bose’s work, Einstein showed that if a sample of atoms were cooled sufficiently, a large fraction of them would settle into the single lowest possible energy state in the container. In Mathematical terms, their individual wave equations would merge, and each atom would become indistinguishable from one another.” In 1995, the first Bose-Einstein Condensate was produced in a vapor of rubidium-87 atoms by Eric. A Cornell and Carl E. Wieman. Shortly after, Wolfgang Ketterle used sodium atoms to produce another sample of Bose-Einstein Condensate. This earned them the Nobel Prize in Physics (2001) “for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms and for early fundamental studies of the properties of the condensates.”
Sources:
Eric A. Cornell and Carl E. Wieman (1998), The
Bose-Einstein Condensate, Scientific American, Vol. 278, No.3, pp. 40-45
M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E.
Wieman and E. A. Cornell (1995), Observation of Bose-Einstein Condensation in a
Dilute Atomic Vapor, Science, New Series, Vol, 269, No. 5221, pp. 198-201
Roahn Wynar, R. S. Freeland, D.J. Han, C. Ryu and D.J.
Heinzen (2000), Molecules in a Bose-Einstein Condensate, Science, New Series,
Vol. 287, No. 5455, pp. 1016-1019.
Simon L. Cornish and Donatella Cassettari (2003), Recent
Progress in Bose-Einstein Condensation Experiments, Philosophical Transactions:
Mathematical, Physical and Engineering Sciences, Vol. 361, No. 1813, pp.
2699-2713.
Keith Burnett (1995), An Intimate Gathering of Bosons,
Science, Vol. 269, No. 5221, pp. 182-183.
Sidney D. Drell (1977), Elementary Particle Physics,
Daedalus, Vol. 106, No. 3, Discoveries and Interpretations: Studies in
Contemporary Scolarship, Volume I (Summer, 1977), pp. 15-31.
Sidney Perkowitz (2022), Bose-Einstein Condensate
[online] Last accessed 28 February 2022: https://www.britannica.com/science/Bose-Einstein-condensate
John Toon (2022), Bose-Einstein Condensates Evaluated for
Communicating Among Quantum Computers [online] Last accessed 06 March 2022: https://physics.gatech.edu/news/bose-einstein-condensates-evaluated-communicating-among-quantum-computers#:~:text=The%20individual%20computers%20in%20such,necessary%20for%20a%20single%20computer.
Carroll Sean (2022), The Particle at the End of the
Universe [online] Last accessed 05 February 2022: http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/spinc.html
Jesse Emspak (2018), States of Matter: Bose-Einstein
Condensate [online] Last accessed 05 February 2022: https://www.livescience.com/54667-bose-einstein-condensate.html
Images:
Figure 1: https://en.wikipedia.org/wiki/Elementary_particle
Figure 2: https://www.istockphoto.com/illustrations/kelvin-scale
Figure 3: NIST/JILA/CU-Boulder
Comments
Post a Comment
Comments with names are more likely to be published.