Smallest Force Ever Measured Detected with the Help of Ultracold Atoms

Most people fixate on the big things--the largest state, the biggest burger, the best athlete. But the small things in life can also be important, and physicists at Berkeley Lab have shown just that. They've managed to detect the smallest force ever to be measured with a groundbreaking technique.

Using a combination of lasers and a unique optical trapping system that provides a cloud of ultracold atoms, the scientists measured a force of just 42 yoctonewtons. A yoctonewton is one septillion of a newton. In fact, there are about 3 x 10^23 yoctonewtons in just one ounce of force.

"We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finess optical cavity and measured the resulting motion optically," said Dan Stamper-Kurn, one of the researchers, in a news release. "When the driving force was resonant with the cloud's oscillation frequency, we achieved a sensitivity that is consistent with theoretical predictions and only a factor of four above the Standard Quantum Limit, the most sensitive measurement that can be made."

While this is certainly impressive, though, it's likely that it's possible to get even closer to the SQL for force sensitivity. In theory, a combination of colder atoms and improved optical detection efficiency should allow researchers to detect an even smaller force. This could mean that, eventually, physicists may be able to measure the SQL itself-or at least very close to it.

"A scientific paper in 1980 predicted that SQL might be reached within five years," said Sydney Schreppler, one of the researchers. "It took about 30 years longer than predicted, but we now have an experiment set-up capable both of reaching very close to the SQL and of showing the onset of different kinds of obscuring noise away from that SQL."

The findings are published in the journal Science.