What is Bose-Einstein Condensate

The early 1900s saw a large number of intellectuals come up with a number of astonishing inventions and discoveries. Among them was a physicist named Satyendra Nath Bose. He was studying the behavior of light and its properties. The study led to the conclusion, that light consists of a number of 'packets' called 'quanta' or 'photons'. Bose theorized that the behavior of these packets was either counted as similar or different, based on certain conditions. He sent his papers to Albert Einstein, who was widely acclaimed for his scientific discoveries. Einstein got those papers published, along with his own additions to the theory. The new state of matter, which they believed, could be simulated at absolute zero temperature, was called 'Bose-Einstein Condensate'.

The Condensate
It is an effect observed on 'bosons' (particles that obey Bose -Einstein statistics, but not Pauli's exclusion principle) due to the application of quantum mechanics. When temperatures close to absolute zero temperature are achieved, a peculiar change takes place in the substance. The atoms begin to condense and clump together. This process is achieved within a few billionths of a degree, resulting in BEC. The atoms form a cluster and occupy the same place in space, as if it were a single big atom. Mathematically, the positions of these atoms are described by their individual wave-equations, which specify their exact location in space. On solving these equations, it can be conclusively proved that each atom becomes a single entity or in ordinary language, a single blob under certain conditions. In scientific terms, BEC is a statistical distribution of similar and indistinguishable bosons, over the different energy levels achieved in a thermal equilibrium.

In order to understand the BEC, it is important to know what are bosons and fermions. Electrons, protons, neutrons, quarks are examples of fermions. According to quantum mechanics, these particles are always spinning and this spinning motion is a multiple of 1/2. Bosons, on the other hand, have an integral spin number such as 0,1,2,3 and so on. Thus, all the half-integer spins are associated with the fermions. A bound state of matter consisting of two fermions behaves like a boson, because the half-spin associated with a fermion is either neutralized, if the spin is in opposite direction, (1/2 -1/2) or added (1/2+1/2) if it is in the same direction. Both cases result in the creation of a boson. On the other hand, a bound state of bosons will always yield bosons only, because integers will always add or subtract to an integer number.

The point is, fermions cannot occupy the same space while bosons can, which is in accordance with Pauli's exclusion principle. Two electrons spinning in the same direction cannot be put close to each other, as it never happens in the natural scheme of things, whereas bosons can in fact, overlap each other in their motion. The position of an object, according to wave-theory, is always fixed in a certain region in space. However, certain conditions produce a state, wherein it is impossible to distinguish the position of an individual object, relative to the others. Consider a situation, where you are standing on top of a cliff, watching your friend, who is standing at the foot of the hill. He appears to be a single dot from that height. If in the next half an hour, hundreds of people crowd the area, you will not be able to spot or distinguish that particular 'dot', that is your friend!

This is exactly the situation that develops in a Bose-Einstein condensate. When millions of atoms are condensed, a unique state of matter is achieved, where the identity of each is lost. Even if there was a provision of marking each atom, you won't be able to identify or pick out the required one in a condensate. By the end of 2001, there were around 36 laboratories in the world which could create conditions, to carry out the Bose-Einstein condensation. The theory has led to breakthrough research in the field of superconductivity, superfluids study or devising extremely small computer chips. Thus, BEC has been a great visionary accomplishment of the 20th century.