The coldest experiment on Earth
At 10:54 a.m. on June 5, 1995, inside a laboratory at JILA, physicists Eric Cornell and Carl Wieman achieved a temperature colder than any known natural place in the universe. They cooled a cloud of rubidium-87 atoms to 170 nanokelvin—just 170 billionths of a degree above absolute zero (-273.15 °C or -459.67 °F). At this extreme temperature, the atoms stopped behaving as individual particles and condensed into a single quantum state. This was the first creation of a Bose-Einstein Condensate (BEC), a new form of matter predicted 70 years earlier.
The theoretical foundation for this state began with Satyendra Nath Bose in the 1920s. He developed a new statistical method to describe photons. Albert Einstein extended Bose's work to atoms, predicting that at sufficiently low temperatures, bosons (a class of particles) would fall into the lowest possible quantum state, their wave functions overlapping until they became indistinguishable. For seven decades, this remained a theoretical concept. No one had the technology to reach the required temperatures and densities until the work at JILA. The achievement earned Cornell and Wieman, along with Wolfgang Ketterle of MIT who created a condensate a few months later, the 2001 Nobel Prize in Physics.
Forging a superatom
Creating the condensate required a two-stage cooling process. The first stage used lasers to slow the atoms. Laser beams were directed at a vapor of rubidium atoms from all six directions, creating a kind of "optical molasses" that chilled the cloud to about 10 microkelvins.
This temperature, while extremely cold, was not enough to form a condensate. The second stage involved transferring the laser-cooled atoms into an innovative magnetic trap. The physicists then initiated evaporative cooling by using a radio-frequency field to remove the most energetic atoms from the trap. As the hottest atoms escaped, the average temperature of the remaining atoms dropped. After several minutes of evaporation, the surviving 2,000 rubidium atoms reached the critical temperature of 170 nK. They then collapsed into the single quantum entity of a Bose-Einstein Condensate, which persisted for 15 to 20 seconds.