Bose–Einstein condensates (BECs) are states of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero (that is, very near 0 K or −273.16 °C). 

Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point macroscopic quantum phenomena become apparent, these include:  superfluidity and superconductivity; other examples include the quantum Hall effect and concerted proton tunneling in ice

BECs are formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to ultra-low temperatures. 

Due to the unique properties of the condensate, Lene Hau showed that light can either be stopped or slowed down significantly to the velocity of 17 meters per second, resulting in an extremely high refractive index.

This state was first predicted, generally, in 1924–25 by Satyendra Nath Bose and Albert Einstein.

A little more on the history of this special state

Satyendra Nath Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons), in which he derived Planck's quantum radiation law without any reference to classical physics. 

Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the Zeitschrift für Physik, which published it. Einstein then extended Bose's ideas to matter in two other papers. 

 The result of their efforts is the concept of a Bose gas, governed by Bose–Einstein statistics, which describes the statistical distribution of identical particles with integer spin, now called bosons. 

Bosons, which include the photon as well as atoms such as helium-4 (4He), are allowed to share a quantum state. 

Einstein proposed that cooling bosonic atoms to a very low temperature would cause them to fall (or "condense") into the lowest accessible quantum state, resulting in a new form of matter.

In 1938 Fritz London proposed BEC as a mechanism for superfluidity in 4He and superconductivity.

Velocity-distribution data (3 views) for a gas of rubidium atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate. Left: just before the appearance of a Bose–Einstein condensate. Center: just after the appearance of the condensate. Right: after further evaporation, leaving a sample of nearly pure condensate.
image: wikipedia NIST/JILA/CU-Boulder - NIST Image. 

On June 5, 1995 the first gaseous condensate was produced by Eric Cornell and Carl Wieman at the University of Colorado at Boulder NIST–JILA lab, in a gas of rubidium atoms cooled to 170 nanokelvins (nK). 

Shortly thereafter, Wolfgang Ketterle at MIT demonstrated important BEC properties. For their achievements Cornell, Wieman, and Ketterle received the 2001 Nobel Prize in Physics.

Many isotopes were soon condensed, then molecules, quasi-particles, and photons in 2010. 

Properties include vortexes and attraction to repulsion

As in many other systems, vortices can exist in BECs. These can be created, for example, by 'stirring' the condensate with lasers, or rotating the confining trap. The vortex created will be a quantum vortex. 

Experiments led by Randall Hulet at Rice University from 1995 through 2000 showed that lithium condensates with attractive interactions could stably exist up to a critical atom number. 

May help show behaviours of supernova explosions

After Quench cooling the gas, they observed the condensate to grow, then subsequently collapse as the attraction overwhelmed the zero-point energy of the confining potential, in a burst reminiscent of a supernova, with an explosion preceded by an implosion.

source adapted from: Bose–Einstein condensate. (2017, April 25). In Wikipedia, The Free Encyclopedia. Retrieved 10:43, April 28, 2017, from