(PhysOrg.com) -- Scientists in Australia and the US have discovered that trapped ions are "exquisitely sensitive" force detectors, and have used them to record the tiniest forces ever measured.
The researchers, from the University of Sydney, in NSW Australia, and the National Institute of Standards and Technology in Colorado, USA, have used their system to measure forces three orders of magnitude smaller than any previously measured force. The forces were as small as 174 yoctonewtons, or 174 septillionths of a newton (174 x 10-24 newtons).
Professor Michael Biercuk of the University of Sydney and colleagues developed their system using a Penning trap, a device in which ions are confined in two dimensions by a strong magnetic field, and in the third dimension by a weak electrostatic field. About 60 beryllium ions are held in the trap and kept very cold to eliminate motion due to thermal effects. The ions are charged and normally line up in the center of the trap. They are affected by any stray electrical or magnetic fields, which cause them to vibrate and become displaced from the center.
Any movement produced by an applied force is detected by reflecting a laser off the ions and measuring any Doppler shift in the frequency of the light. (The light’s frequency is slightly higher when the ion is moving towards the detector, and lower when moving away.) The detection system was able to measure the strength forces in the yoctonewtons range.
Until the present experiment, the smallest forces ever measured were in the attonewton range (10-18 newtons). These measurements were made coupling micro- or nano-fabricated resonators to systems such as single-electron transistors, or superconducting microwave cavities. The ability to detect tiny forces is important for applications such as tests of fundamental physical phenomena and precision spin-resonance imaging.
The researchers hope to eventually be able to measure a single yoctonewton by using a single beryllium ion in the trap, and they believe their experiments will lead to the development of a new class of sensors based on trapped ions. Their results are published online in the pre-publication blog ArXiv.
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