Microwave-powered fridges for nanoscale mechanical resonators
This microwave 'fridge' is unlike the one in your kitchen. Rather than chilling pints of milk, it cools tiny devices called 'micro' or 'nano-scale mechanical resonators' to a decidedly frosty –170 ºC. It is important to cool down these devices, which look and behave like tiny diving boards (the simplest type of mechanical resonator, with a well-defined resonant frequency, like a tuning fork), so that they can be measured accurately.
Heat is a killer when trying to make an accurate measurement. Any material that is warmer than absolute zero (–273 ºC) will have atoms moving around inside it, and this makes it very difficult to measure accurately (just as it would be very difficult to weigh a person who was jumping around on the scales).
Now imagine how much easier it would be to weigh the person if they were standing still - this is effectively what NPL has achieved. We have developed a technique that selectively cools down just the property of a sample that needs to be measured. This selective cooling saves an enormous amount of energy, as it means you don't have to waste energy cooling an entire sample when you are only interested in cooling and measuring a tiny fraction of it.
This technique will be of great use in nano-scale and quantum physics as it allows scientists to detect tiny changes in physical factors such as mass, force and displacement by measuring accurately changes in the resonant frequency of the diving board. This means it can be used in applications where highly sensitive detection is needed, such as bio-analytical screening for viruses (by catching a virus on the diving board!). In the longer term this technique could lead to development of even more sensitive 'quantum' diving boards which could be used to examine the really big questions of quantum physics, such as "At what scale do quantum effects break down?".
For more information on this research read 'Excitation, detection, and passive cooling of a micromechanical cantilever using near-field of a microwave resonator', published in the journal Applied Physics Letters 95, 113501 (2009) doi:10.1063/1.3224912 on 16 September 2009.
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