Observing objects in quantum mechanics is difficult, as it forces the object in question to assume a particular state. A group of researchers led by Gerardo Adesso from the University of Nottingham have developed a system that relies on quantum correlation in order to measure the angle of rotation of an object. The results have been published in Physical Review Letters, and also on arXiv.org.

Of course, describing how this works can be somewhat tricky, so the researchers have developed an analogy to make more sense of things. If a student named Alice is preparing for a hard test, she may rely on her friend Bob to help her, Adesso explained to Phys.org. To score as high as she can, she and Bob would need to anticipate what material would show up on the exam and prepare for all possibilities.

As it translates to quantum metrology, in order to measure the angle of rotation, the system needs to be prepared in a way that allows it to be sensitive enough to rotate from any angle. The more insensitive the direction it can be rotated is similar to Alice studying for the most difficult possible exam.

Quantum systems don’t exactly have helpful friends to help prepare like Alice does, but they can be correlated with other systems. The amount of quantum discord between the two systems allows researchers to estimate the direction of the rotation angle. This information allows them to make more precise measurements. Within the exam analogy, this would be like a friend (represented in the diagram by Charlie) who is feeding answers to Alice and helping her to cheat.)

This study itself was only proof of principle to show the value of quantum correlation for obtaining precise measurements, though future studies may build off of it and the technology could one day be incorporated into resilient and secure communications systems, gravitational wave detection, biomedical imaging, and more.

"More fundamentally, I am interested in understanding the physical properties of general quantum correlations and characterizing their resilience to noise,” Adesso told Phys.org. “The picture we had in this paper was for the estimation of unitary transformations. If the transformations are noisy, discord can be degraded but in some cases it gets enhanced instead. One can then check whether this would result in a noise-empowered precision in estimation. Perhaps this is already exploited in natural phenomena, where coherence is found to flourish in noisy environments and has a functional role for the system's optimization. After all, we clearly showed how coherence is nothing but the daughter of quantum discord."

[Hat tip: Lisa Zyga, Phys.org]