New ‘refrigerator’ super-cools molecules to nanokelvin temperatures

For years, researchers have actually tried to find methods to cool molecules down to ultracold temperatures, at which point the molecules ought to slow to a crawl, enabling researchers to specifically manage their quantum habits. This might make it possible for scientists to usage molecules as complicated bits for quantum computing, tuning person molecules like small knobs to perform numerous streams of computations at a time.

While researchers have super-cooled atoms, doing the exact same for molecules, which are more complicated in their habits and structure, has actually shown to be a much larger difficulty.

Now MIT physicists have actually discovered a method to cool molecules of salt lithium down to 200 billionths of a Kelvin, simply a hair above outright absolutely no. They did so by using a method called collisional cooling, in which they immersed molecules of cold salt lithium in a cloud of even cooler salt atoms. The ultracold atoms functioned as a refrigerant to cool the molecules even further.

Collisional cooling is a basic method utilized to cool off atoms utilizing other, cooler atoms. And for more than a years, scientists have actually tried to supercool a variety of various molecules utilizing collisional cooling, just to discover that when molecules hit atoms, they exchanged energy in such a method that the molecules were heated up or damaged at the same time, called “bad” accidents.

In their own experiments, the MIT scientists discovered that if salt lithium molecules and salt atoms were made to spin in the exact same method, they might prevent self-destructing, and rather taken part in “good” accidents, where the atoms removed the molecules’ energy, in the type of heat. The group utilized accurate control of electromagnetic fields and a complex system of lasers to choreograph the spin and the rotational movement of the molecules. As outcome, the atom-molecule mix had a high ratio of great-to-bad accidents and was cooled off from 2 microkelvins to 220 nanokelvins.

“Collisional cooling has been the workhorse for cooling atoms,” includes Nobel Prize laureate Wolfgang Ketterle, the John D. Arthur teacher of physics at MIT. “I wasn’t convinced that our scheme would work, but since we didn’t know for sure, we had to try it. We know now that it works for cooling sodium lithium molecules. Whether it will work for other classes of molecules remains to be seen.”

Their findings, released in the journal Nature, mark the very first time scientists have actually effectively utilized collisional cooling to cool molecules down to nanokelvin temperatures.

Ketterle’s coauthors on the paper are lead author Hyungmok Son, a college student in Harvard University’s Department of Physics, together with MIT physics college student Juliana Park, and Alan Jamison, a teacher of physics at the University of Waterloo and going to researcher in MIT’s Research Laboratory of Electronics.

Reaching ultralow temperatures

In the past, researchers discovered that when they attempted to cool molecules down to ultracold temperatures by surrounding them with even cooler atoms, the particles clashed such that the atoms imparted additional energy or rotation to the molecules, sending them flying out of the trap, or self-destructing completely by chain reactions.
The MIT scientists questioned whether molecules and atoms, having the exact same spin, might prevent this result, and stay ultracold and steady as an outcome. They looked to test their concept with salt lithium, a “diatomic” particle that Ketterle’s group try outs routinely, including one lithium and one salt atom.

“Sodium lithium molecules are quite different from other molecules people have tried,” Jamison states. “Many folks expected those differences would make cooling even less likely to work. However, we had a feeling these differences could be an advantage instead of a detriment.”

The scientists fine-tuned a system of more than 20 laser beams and numerous electromagnetic fields to trap and cool atoms of salt and lithium in a vacuum chamber, down to about 2 microkelvins — a temperature level Son states is optimum for the atoms to bond together as salt lithium molecules.

Once the scientists were able to produce adequate molecules, they shone laser beams of particular frequencies and polarizations to manage the quantum state of the molecules and thoroughly tuned microwave fields to make atoms spin in the exact same method as the molecules. “Then we make the refrigerator colder and colder,” states Son, referring to the salt atoms that surround the cloud of the recently formed molecules. “We lower the power of the trapping laser, making the optical trap looser and looser, which brings the temperature of sodium atoms down, and further cools the molecules, to 200 billionths of a kelvin.”

The group observed that the molecules were able to stay at these ultracold temperatures for up to one second. “In our world, a second is very long,” Ketterle states. “What you want to do with these molecules is quantum computation and exploring new materials, which all can be done in small fractions of a second.”

If the group can get salt lithium molecules to have to do with 5 times cooler than what they have actually up until now attained, they will have reached a so-called quantum degenerate routine where person molecules end up being identical and their cumulative habits is managed by quantum mechanics. Kid and his coworkers have some concepts for how to accomplish this, which will include months of operate in enhancing their setup, along with obtaining a new laser to incorporate into their setup.

“Our work will lead to discussion in our community why collisional cooling has worked for us but not for others,” Son states “Perhaps we will soon have predictions how other molecules could be cooled in this way.”


This research study was moneyed, in part, by the National Science Foundation, NASA, and the Samsung Scholarship.

Written by Jennifer Chu, MIT News Office

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