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  • Ritwik Mishra


Matter, at the school level, is broadly categorised into 3 states: solid, liquid and gas. However, there are actually five known states of matter, plasma that’s above gas in terms of temperature(like lightning bolts), and Bose-Einstein condensates which are at the extreme bottom of the temperature scales. The temperature required to form these condensates is even lower than the temperature for superconductors, that is, near absolute zero!

One of the most interesting facts about Bose-Einstein condensates is that they comprise a special kind of particle called bosons. There are three types of bosons: the W, the Z and the Higgs. Particles can be divided into two categories: bosons and fermions. Fermions are particles that have non-integer spins or fractional spins like positive half or negative half, and bosons are particles that have integer spins like a positive one, a negative one, and zero. Spin is the last quantum number of the quantum number set. For example, rubidium at low temperatures acts as a boson because the net spin of the atom becomes integral. That is why rubidium was used to create Bose-Einstein condensates. Bosons are used to make Bose-Einstein condensates because at very low temperatures multiple bosons can share a quantum state. This basically means that the amplitude of their quantum wavelength (which governs their movement) is greater than the space between them. So, in essence, a group of bosons are existing at one given point in space. Fermions do not have this ability.

One of the most ingenious ways that the temperature requirement was met was with laser cooling. This might seem counterintuitive at first, but this method was very effective. This involved shooting the particles that were moving in the mass with lasers that were just above the energy levels that the particles tend to absorb: thus the particles would be considerably slowed down by the lasers and the angle of their motion would change. Some energy would be absorbed by the particles which they later lose, but because their angle of motion changes the magnitude of their velocity is reduced and hence, the particles have less kinetic energy than they did before the laser cooling process which reduces their temperature and lowers the temperature enough for the condensate to be created.

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