Anyone who has studied the basics of quantum mechanics (or seen Breaking Bad) has heard of Heisenberg. In 1927, Werner Heisenberg published the uncertainty principle that explained that it was impossible to know the position and the momentum of a particle with the same degree of accuracy. This limitation, quite unknown to most of us, affects a number of unrelated scientific techniques like medical MRI, NMR spectroscopy, atomic clocks etc. Now, years later, scientists have devised a method which can avoid this limitation.
Uncertainty principle, what?
Before we proceed, here’s an oversimplified explanation of the uncertainty principle. In short, it basically says that we cannot know details about subatomic particles unless we measure, however, paradoxically, the act of measuring a particle’s position or spin, changes the position or spin. For example, measuring a particle’s position requires it to be hit by a second particle, and then checking the change in momentum of this second particle. Of course, it goes without saying, that this also changes the momentum of the first particle, which means it is disturbed from it’s “position”. On the other hand, measuring the spin (spin angular momentum) involves measuring how light is polarised by the particle. Since we’re talking subatomic particles, interactions with photons actually change the spin itself – slightly. This means that we change the spin (minimally) by the very act of measuring it, and thus have tiny errors in our measurements.
Scientists at the Institute of Photonic Sciences in Barcelona have developed a new method to measure both these quantities with less disturbance than was previously thought possible – and thus increasing the accuracy of the measurements by a large amount.
They discovered that they could represent the spin as two angles – an azimuthal angle (like lines of longitude on a globe), and the polar angle (like latitude). They also learned that measuring the longitudinal (azimuthal) angle is enough to calculate the particle’s spin, which means light polarised in a way to have minimal interaction with polar spin (latitude) should be more accurate. This is a gross oversimplification, of course, and we honestly don’t really understand the science being done here, but then few people in the world do.
Was it easy?
Hell no! “Not all the technologies we used for the experiment existed when we started,” says Giorgio Colangelo, another member of the research team. “We had to design and develop a particular detector that was fast enough and with very low noise. We also had to improve a lot the way we were preparing the atoms and find a way to efficiently use all the dynamic range we had in the detector.”
This technique does immediately benefit atomic timekeeping and certain other techniques. But due to certain limitations, MRI and NMR techniques are yet to see direct benefits. The scientists are hoping that might happen eventually, after some breakthroughs in other fields. The quantum world is weird, but we’re seemingly making discoveries we never thought possible. We’re far from masters of it all, but research like this chips away slowly at the barriers that prevent us from understanding our universe.
Reference: Scientific American