Bose-Einstein Condensates Can Be Made Faster Now, Thanks To MIT Researchers

Atoms are in a constant state of random motion. Atoms constantly shoot past and collide with each other. But, in 1995, the first Bose-Einstein condensate was created by drastically cooling the atoms. This quantum state showed the world that when these atoms hit a point just above zero degrees, they enter into what has been described by researchers as a “zombie-like” state.

When they reach these extremely cool temperatures, the atoms stop their random, frantic movement and start moving very slowly in one wave-like formation, this quantum form of matter is the Bose-Einstein condensate.

Understanding Bose-Einstein condensation is very important in the study of magnetism and superconductivity. Scientists from across the globe believe that cooling down atoms to a much more stable state of being can help channel magnetic field and provide major breakthroughs in the field of superconductivity where resistance is frowned upon.

But, creating these Bose-Einstein condensates is currently a very time and energy intensive process that has a very low output.

It involves cooling down a cloud of atoms with a laser and then using evaporative cooling to further reach near-zero temperatures.

Several laser beams from different angles are trained at the cloud of atoms. The photons crowd the cloud, limiting the movement of atoms. This takes the atoms close to the “zombie-like” state of the final condensate. With each collision between atoms in the cloud, the photons compress the cloud of atoms further. But, as the cloud grows denser, temperature inside the cloud starts rising. The lasers’ are turned off atthis point and the atoms allowed to cool like a warm cup of coffee.

But this method is very slow. Over 99 percent of the original atoms scatter away from the cloud during the evaporation part of the procedure.

“In the end, you have to start with more than 1 million atoms to get a condensate consisting of only 10,000 atoms,” Vladan Vuletić, the Lester Wolfe Professor of Physics at MIT said in a press release on their website. “That’s a small fraction and a big drawback,” he added.

MIT physicists have now invented a new technique to cool atoms into condensates which is faster than the conventional method and conserves a much larger number of atoms from the cloud, giving us much more condensate for any given cloud size.

The team used a new process of laser cooling to cool a cloud of rubidium atoms all the way from room temperature to 1 microkelvin, or less than one-millionth of a degree above absolute zero.

They then switched over to a method known as Raman cooling, in which they used a set of two laser beams to cool the atoms further. The first laser beam was tuned in such a way that its photons when absorbed by atoms, created a light-induced magnetic field in the cloud. The atoms’ energy effectively gets magnetized and this force slows down the atoms in the cloud. The other laser helped the cloud maintain the original total energy.

The second laser played a much more sniper-like role. Slower atoms are targeted by this laser so that it removes the atoms’ energy further causing very high degrees of cooling inside individual atoms in the cloud.

“Ultimately the photons take away the energy of the system in a two-step process,” Vuletić says. “In one step, you remove kinetic energy, and in the second step, you remove the total energy and reduce the disorder, meaning you’ve cooled it” This means that the two, targeted laser action on the cloud enables a much higher rate of cooling.

By removing the kinetic energy, or converting it into magnetic energy, the team essentially did away with the random motions of atoms in the cloud.

According to the report, the researchers were able to control the rising heat in the cloud seen in the previous model by turning the lasers away from atomic resonance. This allows the excess light to escape easily without causing the heating effect seen in the older method.

This means incoming photons are less likely to be absorbed by atoms, triggering vibrations and heat. Instead, every photon bounces off just one atom. By directing the lasers away from the vibrations in the atomic nucleus (resonance) the team was able to ensure that it was scattered away by the first atom it encounters, reducing the time it spent in the cloud which avoids heating due to overcrowding.

“Before, when a photon came in, it was scattered by, say, 10 atoms before it came out, so it made 10 atoms jitter,” Vuletić says. “If you tune the laser away from resonance, now the photon has a good chance of escaping before hitting any other atom. And it turns out by increasing the laser power, you can bring back the original cooling rate.”

The results of the study published in journal Science, the team were able to use this technique to cool rubidium atoms from 200 microkelvins to 1 microkelvin in just 0.1 seconds. This makes this mathematically 100 times faster than the conventional method.

The results of the new method also showed a whopping 1,400 atoms left back from the original cloud of 2,000. This showed that 70 percent of the atoms were retained compared to the 1 percent retention of the old method.