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Physicists using a combination of lasers and a unique optical trapping system that provides a cloud of ultracold atoms say they have detected what is believed to be the smallest force ever measured. The researchers, from the Lawrence Berkeley National Laboratory and the University of California Berkeley, measured a force of approximately 42 yoctonewtons. A yoctonewton is one septillionth (that’s 1 followed by 24 zeroes) of a newton, the standard unit of force. “We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity and measured the resulting motion optically,” says Dan Stamper-Kurn, a physicist with Berkeley Lab’s Materials Sciences Division and with the UC Berkeley Physics Department. “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.” The team’s research was published in the journal Science.

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