The record for the coldest temperature ever achieved has been broken with the cooling of rubidium gas to 38 picokelvins (3.8 * 10-11 K). The work could lead to new insights into quantum mechanics.
Temperature is a measure of the energy in atoms' or molecules' vibrations. The lowest temperature theoretically possible is absolute zero – 0 K or −273.15 ºC (−459.67 ºF) – which would require a complete cessation of movement. That's probably impossible practically, but for decades physicists have shown we can get very, very close by using lasers to damp atomic motion.
In Physical Review Letters German scientists have reported going closer to zero than ever before.
Professor Ernst Rasel of Leibniz Universität Hannover and co-authors placed 100,000 rubidium atoms inside a magnetic trap at the top of the University of Bremen's 110 meter (360 feet) tall Bremen drop tower. The trap forms what is called a “matter-wave lens” that by focusing the atoms at infinity cools them to the point that they became a Bose-Einstein Condensate (BEC), a state of matter where collections of atoms can show quantum behavior as if they were a single subatomic particle/wave.
Turning off the trap allows the condensate to expand in all directions, cooling it further. The BEC was then allowed to free-fall down the length of the tower while detectors observed its behavior.
The whole process lasts just two seconds, although modeling suggests 17 seconds is possible, and the authors hope to exploit this longer timeline to explore BEC behavior with the distortions of vibrations removed.
In an accompanying viewpoint article the University of Portsmouth's Dr Vincenzo Tamma, who was not involved with the research, said the work could “test gravity at the quantum level.” Interference patterns in the BEC are determined in part by gravitational effects. With inconsistencies between our understanding of quantum physics and general relativity's description of gravity representing perhaps physics' greatest unsolved puzzle, the work provides an opportunity to explore physics at its most fundamental. Tamma also sees potential for the technique to search for certain forms of dark matter.
A hundred thousand atoms may sound like a lot, but it's actually about 50 million times less than make up the head of a pin, give or take a bit for variation in atomic, and pin-head, size. The coldest temperature achieved in something you could see was set when a 400 kilogram (882 pound) block of copper was cooled to 0.006 K. To get there, researchers required lead that had been mined thousands of years ago, giving time for radioactive isotopes formed through exposure to other radioactive elements in the ore to decay. This was provided through the fortuitous (for us) discovery of a Roman galley that sank of the coast of Sardinia bearing Spanish lead intended for use in the Roman civil wars.
[H/T: Popular Mechanics]