For example nuclear magnetic resonance and other spectroscopies have a important property that they works only at a certain frequency (or short interval of them) due to quantum mechanical discrete origin of microworld. Let us assume we have a very low electromagnetic signal of some frequency in space on in electric circuit. This signal amplitude is much less than a noise amplitude. We do see it in our oscilloscope. But for example for nuclear magnetic moments ensemble it may be sufficient (and even rather good!) to absorb it. Then we can register this NMR by receiver electronics.
Dear sirs, are there such devices? And funny question: could we remotely by such a way to register, say encephalographic activity of our our brain, say directly "our thoughts" ?? :))) Yes there frequencies are very low. But there is field cycling NMR or NMR in even zero or arbitrary magnetic field.
Any comments?
I do not go into the wider aspects of the present question and suffice to mention that the fractional charge of the quasi-particles in the fractional quantum Hall (FQH) regime has been measured on the basis of the quantum shot noise. For this, you may wish to consult, for instance, the attached publication by de-Picciotto et al. (Nature 389, 162-164 (1997)).
http://www.nature.com/nature/journal/v389/n6647/full/389162a0.html
Thank you for the article.I did not think about quantum noise (but now it is popular with gravitational waves), I thought nuclear magnetic resonance can be very useful even for detection of noisy signals of any type.
You are welcome Anatoly.
I think I do not understand the question. Regarding the NMR, it is connected with resonant absorption and emission of radiation, which has to do with matching of frequencies and not with the amplitude, or intensity, of the absorbed and emitted radiation.
In general, with very weak signals one uses an array of detectors (astronomers in particular use arrays of dishes). When the nature of noise is known or can be accurately modelled, a great deal can be achieved by the statistical analysis of the measured signal. For some relevant details, consult the subject of lock-in amplifier.
https://en.wikipedia.org/wiki/Lock-in_amplifier
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