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Bose Einstein Condensate

We explain what Bose-Einstein condensate is, its origin, characteristics, how it is obtained and its applications. bose einstein condensate

Bose Einstein Condensate
Figure 1.- In Bose Einstein condensate, the low temperature bosons are all kept in the lowest energy state.

What is Bose Einstein condensate?

Bose Einstein condensate (CBE) is a state of aggregation of matter , just like the usual states: gaseous, liquid and solid, but which takes place at extremely low temperatures, very close to absolute zero. bose einstein condensate

It consists of particles called bosons, which at these temperatures are located in the lowest energy quantum state, called the ground state . Albert Einstein predicted this circumstance in 1924, after reading the papers sent to him by the Indian physicist Satyendra Bose on the statistics of photons.

It is not easy to obtain the necessary temperatures in the laboratory for the formation of Bose-Einstein condensate, so it took until 1995 to have the necessary technology.

That year the North American physicists Eric Cornell and Carl Wieman (University of Colorado) and later the German physicist Wolfgang Ketterle (MIT), managed to observe the first Bose-Einstein condensates. The Colorado scientists used rubidium-87, while Ketterle made it through a highly dilute gas of sodium atoms. bose einstein condensate

Thanks to these experiments, which opened the doors to new fields of research in the nature of matter, Ketterle, Cornell and Wieman were awarded the Nobel Prize in 2001.

The very low temperatures make it possible for the atoms of a gas with certain characteristics to form such an orderly state that they all manage to acquire the same reduced energy and amount of movement, something that does not happen in ordinary matter. bose einstein condensate

Characteristics of Bose-Einstein condensate bose einstein condensate

Let’s look at the main characteristics of Bose-Einstein condensate:

  • Bose-Einstein condensate occurs in gases made up of very dilute bosonic atoms.
  • The atoms in the condensate remain in the same quantum state: the ground or lowest energy state.
  • Extremely low temperatures are required, just a few nano-kelvins above absolute zero. The lower the temperature, the wave behavior of the particles is more and more evident.
  • In principle, matter in the Bose Einstein condensate state does not exist in nature, since to date no temperatures below 3 K have been detected in the universe.
  • Some CBEs show superconductivity and super-fluidity, that is, lack of opposition to the passage of current, as well as viscosity. bose einstein condensate
  • The atoms in the condensate, all being in the same quantum state, present uniformity in their properties.

Origin of Bose-Einstein condensate

When you have a gas enclosed in a container, normally the particles that compose it keep sufficient distance from each other, interacting very little, except for occasional collisions between them and with the container walls. Hence the well-known ideal gas model derives.

However, the particles are in permanent thermal agitation, and temperature is the decisive parameter that defines the speed: the higher the temperature, the faster they move.

And while the speed of each particle can vary, the average speed of the system remains constant at a given temperature.

Fermions and bosons bose einstein condensate

The next important fact is that matter is made up of two types of particles: fermions and bosons, differentiated by spin (intrinsic angular momentum), an entirely quantum quality.

The electron, for example, is a fermion with a semi-integer spin, while the bosons have an integer spin, making their statistical behavior different. bose einstein condensate

Fermions like to be different and that is why they obey the Pauli exclusion principle, according to which there cannot be two fermions in the atom with the same quantum state. For this reason the electrons are located in different atomic orbitals and thus do not occupy the same quantum state.

On the other hand, bosons do not adhere to the exclusion principle, so they have no problem in occupying the same quantum state. bose einstein condensate

Dual nature of matter

Another key fact in understanding CBE is the dual nature of matter: wave and particle at the same time.

Both fermions and bosons can be described as a wave with a certain extension in space. The wavelength λ of this wave is related to its momentum or momentum p , through the De Broglie equation:  bose einstein condensate

Dual nature of matter

Where h is Planck’s constant, whose value is 6.62607015 × 10 -34 Js

At high temperatures, thermal agitation predominates, which means that the momentum p is large and the wavelength λ is small. Atoms thus show their properties as particles.

But when the temperature drops, the thermal agitation decreases and with it the momentum, causing the wavelength to increase and the wave characteristics prevail. Thus, the particles are no longer localized, because the respective waves increase in size and overlap each other. bose einstein condensate

There is a certain critical temperature under which the bosons end up in the ground state, which is the state with the lowest energy (it is not 0). This is when condensation occurs.

The result is that the bosonic atoms are no longer distinguishable and the system becomes a kind of super atom, described by a single wave function. It is equivalent to viewing it through a powerful magnifying glass with which its details can be appreciated.

How do you get the condensate?

The difficulty of the experiment lies in keeping the system at low enough temperatures so that the de Broglie wavelength remains high.

The Colorado scientists achieved this by using a laser cooling system, which consists of striking the sample of atoms head-on with six beams of laser light to abruptly slow them down and thus drastically decrease their thermal agitation.

Then the colder and slower atoms were trapped by a magnetic field, letting the faster ones escape to further cool the system.

How do you get the condensate
Figure 2.- Velocity distribution of the Rb atoms in the CBE. The white peak represents the largest number of atoms, with an estimated speed of 0.5 mm / s.

Atoms confined in this way managed to form, for brief moments, a tiny drop of CBE, which lasted long enough to be registered in an image.

Applications and examples

CBE applications are currently in full development and it will be some time before they materialize.

Quantum computing

Maintaining consistency in quantum computers is not an easy task, which is why CBEs have been proposed as a means of maintaining information exchange between individual quantum computers.

Reduction of the speed of light

The speed of light in vacuum is a constant of nature, although its value in other media, such as water, may be different.

Thanks to CBEs it is possible to greatly reduce the speed of light, up to 17 m / s, according to some experiments. It is something that will not only allow us to go even deeper into the study of the nature of light, but also its use in quantum computing to store information.

High precision atomic clocks

Cold atoms allow the creation of highly precise atomic clocks, which experience minimal delays over long periods of the order of millions of years, very useful qualities when synchronizing GPS systems.

Simulation of cosmological processes

The atomic forces that are generated in the condensate can help simulate the conditions under which physical processes occur within some notable objects in the universe, such as neutron stars and black holes.

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