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Optical Molasses Colleen Downs Stephanie Pietromonaco Sanjay Talluri Definition Laser cooling technique that cools atoms to temperatures lower than the Doppler limit Uses 3 pairs of counterpropagating circularly polarized laser beams which intersect where the atoms are present History First demonstrated in 1985 by S. Chu Laser cooling first became popular in 1970’s This led to the idea of the Doppler limit Doppler limit – theoretical lowest possible temperature of atoms Falsified with finding of process of optical molasses Optical Trapping Momentum imparted by photons “light pressure” is the greatest portion of this effect Optical Molasses vs. MagnetoOptical Trap (MOT) Both use 3 pairs of counterpropagating laser beams Trap about the same amount of atoms Detection of atoms is easier in MOT because of higher density (less spatial extension) In MOT the magnetic field only acts on atoms as they fall from trap Optical molasses uses circularly polarized lasers Optical molasses breaks Doppler limit In sodium: 40 μK in Optical molasses vs 300 μK in MOT Current Applications GPS (Global Positioning System) Uses time signals from atomic clocks for positioning Atomic clock – use laser cooling for more precise time signals Now: use optical molasses for fountain clocks which are even more precise This leads to better GPS systems Current Applications Lene Hau slowed speed of light from 186,282 miles/second to 38 mph Used a combination of Optical molasses and Bose-Einstein condensate Results could improve computer, TV, and night vision goggles Bose-Einstein Condensate http://www.youtube.com/watch?v=bdzHnAp HM9A Not made til 1995 because didn’t have the appropriate technological “cooking pot” Needed vacuums hundreds of trillions of times lower than atmospheric pressure and temperatures of -459.7˚F (within a few billionths of degree from absolute zero) Process of slowing light atoms Bose-Einstein condensate slows atoms down to 100 mph which can then be trapped in optical molasses Optical molasses creates a clump of cold atoms These cold atoms then undergo evaporative cooling Take out atoms that are still too hot or energetic from the magnetic field Slowing of light First laser – shot across cloud of condensate controls speed of second because of quantum interference Second laser – shot perpendicular to cloud and interferes with the first These 2 lasers result in light traveling at 38 mph Applications of slow light Improve communication Reduce electronic noise Cut power requirements (a million fold!) Ranges from telephones to super computers Hau currently trying to reduce speed of light to 1 cm/second