Physics World

Bose Einstein Condensates and the Cold Atom Lab

Absolute Zero. 0 K. -273.15 °C. Infinite cold. Everything is frozen at this temperature, not a single vibration. The total absence of energy.

 

However you define it, the quest to reach absolute zero has been an ongoing pursuit since it was first theorized in 1848 by William Thomson, or popularly known as Kelvin. The mission is futile, at least as far as we know, since reaching absolute zero is impossible. That hasn’t stopped us from trying. We got within a fraction of a Kelvin using methods like laser cooling.

 

This leads us to Bose-Einstein Condensates (BECs). They were predicted to exist by Indian physicist, Satyendra Bose and Albert Einstein in the early 20th century. Bose studied how photons act and behave. Take into account the two types of photons: bosons (spin number of 1), and fermions (spin number of 1/2). According to the Pauli Exclusion Principle, two fermions cannot have the same set of 4 quantum numbers and will avoid each other, taking to separate quantum levels (energy levels). However, bosons can coexist, sharing the same energy (quantum) state.

 

As temperatures were cooled to near absolute zero, Einstein said that these bosons should come together and merge into a singular quantum state that reduced the overall potential energy of the system. The required equipment to reach these low temperatures did not come through till the 1990s with the invention of laser cooling and trapping. Here, due to radiation pressure, pressure due to the striking of electromagnetic radiation, lasers cooled and trapped atoms by slowing them down. Essentially, they trapped the atoms by restricting their [atoms] “urge” to move around. Magnetic entrapment, where atoms were held in place with no materialistic container, provided to be another useful discovery.

 

In an experiment conducted in 1995 by Eric Cornell and Carl Wieman using the methods outlined above, proved these condensated to exist. By cooling millions of rubidium, or even sodium, atoms, they formed a single wave like matter, a BEC. Bosonic atoms coexisting in a singular quantum state while minimizing the potential energy of the system. These singular layers of condensates don’t behave like any other object or state of matter you are familiar with in the macroscopic world. Instead, they form parallel layers which interfere by the transfer of atoms from one layer to the other.

Velocity-distribution data for a gas of rubidium atoms, determining the discovery of a new phase of matter, the Bose–Einstein condensate. Pic Credit Wikipedia

What good does this do for us?

 

Other than being extremely cool (get it?), the discovery of BECs lead to the invention of atom lasers. These atom lasers produce photons in a singular phase (bosons), with high intensity. These result in highly precise and accurate atomic clocks and has done wonders in terms of circuitry. A BEC can also alter the velocity of light, showing promise for better data storage methods and quantum computers (want to learn more on quantum computers? Stay tuned!).

 

The problem we face with studying BECs is that on Earth, due to the influence of gravity, we are unable to maintain a BEC for longer than a fraction of a second. Gravity pulls together the particles rendering the BEC obsolete.Meanwhile a BEC requires the free movement and gradual spreading of the wave like matter.

 

Recently NASA has launched their Cold Atom Lab (CAL) in which, with the help of lasers, we have achieved the coldest place in the entire known universe. It is approximately 10 billion times colder than space itself (that’s very cold!) and is ever closer to 0 K. NASA plans on launching the CAL into space, where free from gravity and only facing microgravity, BECs can last for up to 10 seconds! Scientists alike are excited to be able to study these condensates in greater depth. Hopefully we can create condensates big enough for the eye to see. Research promises the hopes of “quantum sensors, matter wave interferometers, and atomic lasers,” says Rob Thompson, Project scientist of NASA’s CAL. We have only scratched the surface.

Cold Atom Lab. Pic Credit : NASA

Reference :

  1. Phillips, Tony. “The Coldest Spot in the Known Universe.” NASA, NASA, 30 Jan. 2014, science.nasa.gov/science-news/science-at-nasa/2014/30jan_coldspot.
  2. “The Coolest Spot in the Universe.” Edited by Donna Wu, NASA, NASA, coldatomlab.jpl.nasa.gov/.
  3. Zimmermann, Kim Ann. “Kelvin Temperature Scale: Facts and History.” Live Science, 27 Sept. 2013, www.livescience.com/39994-kelvin.html.
  4. Perkowitz, Sidney. “Bose-Einstein Condensate.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 17 Sept. 2008, www.britannica.com/science/Bose-Einstein-condensate.

 

Preethi is a high school student in United States who is interested in Physics. She loved to discuss any topic related to the subject. In her free time, she loves watching PBS Spacetime and listening to pop music. She hopes to someday major in some area of physics.

Preethi is a high school student in United States who is interested in Physics. She loved to discuss any topic related to the subject. In her free time, she loves watching PBS Spacetime and listening to pop music. She hopes to someday major in some area of physics.