The Laser Cooling That Makes Atomic Clocks So Accurate

Nobel-Prize winning physicist William Phillips admits that “laser cooling” is a somewhat confusing concept. How can light energy, generally thought of as a source of heat, be used to cool something down?  Phillips explains: “Lasers, all light, pushes on stuff. … What we’ve figured out what to do over the years is how to push on atoms in such as way as to make them slow down.” And making these atoms slow down can effectively drop their temperature.

In fact, Phillips and his colleagues discovered that they could slow atoms down enough to get them much, much colder than was originally predicted. “The prediction said that we could get down to temperatures of 240 millionths of a degree. In other words, one-quarter of one-thousandth of a degree above absolutely zero. Pretty cold, right?” In his Big Think interview, Phillips talks about how he and his team managed to use lasers to get atoms a whole lot colder than that.

That breakthrough discovery was a key step in making atomic clocks significantly more reliable. By cooling the atoms in an atomic clock down, Phillips says that we can now measure the ticking frequency far better than before. “When I started doing laser cooling, the very best clocks were accurate to a part in ten to the 13, so that’s one part divided by 1, with 13 zeroes after it … But today, those clocks are a couple and ten to the 16th,” he says. That’s almost three orders of magnitude better.