New accelerometer nears the quantum limit of effectiveness

Ars Technica : A team of researchers from Caltech and the University of Rochester, New York, has created the world’s most sensitive accelerometer. Accelerometers are most familiar in reference to smartphones, which use them to recognize when the device has been rotated. Accelerometers are also used to trigger airbags in cars to inflate during a collision. The new accelerometer, however, is more likely to be used in research labs than in consumer products. The researchers etched a spring-like system out of a silicon nitride membrane, with a mass on the spring of just 10 pg. The resulting system had a resonance frequency of just under 30 kHz and could detect accelerations at a rate of about 15 kHz. That sensitivity is then enhanced further by pairing the mechanical resonator with an optical resonator. Next to the spring the researchers placed a zipper-like structure, which works like a pair of mirrors that bounce light back and forth. Oscillations in the spring stretch the structure, altering the frequency of the light in the optical resonator. The altered frequency allows for easy detection of the otherwise unnoticeable variations in the physical spring’s frequency. The researchers also showed that the device can detect such tiny accelerations that anything smaller would be undetectable because of quantum fluctuations.