I pointed out, few weeks ago, that we are starting to put quantum mechanics at work. Possibly the most esoteric branch of physics that was considered a puzzle for bright minds with no practical application whatsoever.
Here is another possible practical application, worked out by a team at MIT.
Electrons spin is influenced by magnetic fields. There is no clear thresholds, an intensity of the magnetic field that would flip the spin of a single electron. It is, as quantum mechanics tells, a matter of probability. Of course, if you are talking about millions, billions of electrons quantum mechanics probability can predict exactly how many electrons would flip their spin at a certain intensity level of the magnetic spin. Hence, if you can measure the number of electrons that have changed their spin you can determine the intensity of the magnetic field. (I hope I explained this in an understandable way although a physicist might furrow her brow).
The team at MIT have engineered an artificial diamond, as small as a twentieth of of your thumb's nail, with one corner cut (see photo). The diamond, a grid of carbon atoms, has been manufactured to contain nitrogen atoms and "holes" in the carbon grid. These holes are called Nitrogen Vacancies (NV) and contains electrons. In that single sliver of diamond researchers can "store" trillions of NV, hence trillions of electrons.
Through the cut corner they can beam a laser beam that will bounce over and over inside the diamond hitting electrons and pushing them to a higher energy state. This is not a stable state and will decay bringing the electronic back into its stable state and releasing a photon. The geometry of the diamond crystal is such that those photons are finding their way out of the crystal at its corners. A light detector can measure their flow.
The "intensity" of the photon (its wavelength) depends on the spin of the electrons. By measuring the light produced by all electrons it is then possibile to "know" their spin and hence the intensity of the magnetic field.
The sensitivity is three order of magnitude (a thousand times) better than a usual device measuring magnetic field. Also, being a solid state device it is very small and very cheap.
According to the researchers this will allow the creation of sensors for better medical diagnostics, for geological exploration and much more.