The Coldest Place in the Universe is in our Physics Laboratories........ The Bose-Einstein Condensate.........

Bose and Einstein

The Coldest Place in the Universe is on Earth, The Bose-Einstein Condensate

Brief History
In 1924 an Indian Physicist named Satyendra Nath Bose sent a paper to Albert Einstein on the quantum statistics of light quanta, in this paper he manged to do something remarkable at the time and derive Planks constant Radiation Law, without using classical physics, which was a break through at the time, Einstein was impressed and sent the paper to be published that year.
With this new knowledge Einstein being himself expanded on these ideas further, he came up with the Theory of the Bose-Einstein Condensate.

Bose and Einstein

Intro to Quantum Mechanics

I must admit now this is a heavy subject, to understand completely the physics of this concept takes many years of studying. So, I will explain as best I can keeping it simple for readers to understand.
In Quantum Mechanics, we consider particles like atoms as waves, imagine a 3-D bubble vibrating in all directions, the wave is different depending on the energy of the atoms, at higher energies the wave have more complex vibrations for example, they are called spherical harmonics. In the picture below you can imagine for example low energy vibrations around a spherical surface, in the very top picture. It’s not entirely correct but it will help to understand the concept of a BEC.

Spherical Harmoics

The different wave functions are described differently in quantum mechanics, and there is a probability of observing a certain wave function, you can only observe one function and not more at a single time.
With this is mind let’s move forward.

Preparation of a Bose-Einstein Condensate

Due to the atomic structure of Alkali Metals these are first choice when creating a BEC, in this example we will consider Sodium-23 as our choice.
It’s important now to mention that the isotope of sodium-23 is Bosonic, this means the total spin of all particles is an integer, we say the total spin is 1. This is important because is Quantum mechanics, Bosons can exist is the same energetic state in a system, this means that it’s possible that many sodium-23 atoms can have the same energy and the same wave function. Keep this important information in mind.
Sodium is heated in an oven until it becomes a gas and is ejected of the oven in a beam through a small hole, at this point the atoms are very hot about 900 Kelvin, and the most probable velocity of the atoms is about 1000 meters per second. They are highly energetic and must be cooled.

Laser Cooling

The atoms are cooled using a laser beam, this is a complicated process that I will explain in a further post, but for know just accept that the laser can cool the atoms in multiple stages. The Atoms can eventually be cooled to very cold temperature of 0.0000024 Kelvin, that 2.4 Micro Kelvin. At this point the atoms can be trapped in a magnetic field, the higher temperature atoms will populate the top of the trap and colder atoms at the bottom. So, step by step, the trap height is lowered quickly to allow hot atoms to escape, after many steps the average temperature has lowered further, and reach temperatures of Nano-Kelvin, that’s 0.000000001 Kelvin.
This is now absolutely the coldest known place in the Universe. Nothing we know is colder than this.

Now this is where the fun of the Bose-Einstein Condensate starts.

Bose-Einstein Condensate

When the Sodium atoms have been cooled to Nano-Kelvin, nearly 100% of the atomic system exists in the ground state, which is the lowest energy wave function possible for an atom. As I mentioned, Bosons can exist in the same quantum mechanical state, so all the atoms of Sodium are in this ground state, the Bose-Einstein Condensation state. This state is also considered a state of matter, like solid, liquid and gas.

In order to observe a BEC in the Laboratory, we can measure the Velocity distribution of the atoms, we look at how they oscillate over small distances. Absolute zero energy atoms will have no motion, but due to the small but finite temperature there is still some very small oscillations. So scientists look at the number of atoms versus their quadrature (movement in the x-y place).

Bose Einstein Condensate

In the picture above you can see three different stages of a BEC forming. The Height of the graph is the number atoms, the x-y place represents the how the atoms move due to thermal oscillation. On the left, you can see a broad but low peak distribution, this means that a large fraction of the atoms are not in the single wave function of the BEC. The temperature decreases and atomic movement decreases, and more atoms move into a BEC phase, the sharp peak represents atoms in a BEC. If all atoms moved into the BEC phase then the peak would be very sharp and high, for such a situation to occur we would need to cool atoms further towards Zero Kelvin.

Consequences of the BEC
The study of the BEC is useful for understanding how super conductors and superfluid behave. Infact, a BEC can be made in such a way that we can mimic a crystal structure of electrons, this type of BEC allows direct investigation on super conduction behaviour. This study is at the forefront of superconductor research and will be fundamental in under standing super conductors at high temperature.

Material References:-
[1]:- Atomic Physics, Christopher. J. Foot
[2]:- Bose Einstein Condensate in Dilute Gases, C. J. Pethick
[3]:- History of BEC