Physicists from the University of Basel have observed the quantum mechanical Einstein-Podolsky-Rosen paradox in a system of several hundred interacting atoms for the first time. The phenomenon dates back to a famous thought experiment from 1935. It allows measurement results to be predicted precisely and could be used in new types of sensors and imaging methods for electromagnetic fields. The findings were recently published in the journal Science.
How precisely can we predict the results of measurements on a physical system? In the world of tiny particles, which is governed by the laws of quantum physics, there is a fundamental limit to the precision of such predictions. This limit is expressed by the Heisenberg uncertainty principle, which states that it is impossible to simultaneously predict the measurements of a particle’s position and momentum, or of two components of a spin, with arbitrary precision.
A paradoxical decrease in uncertainty
In 1935, however, Albert Einstein, Boris Podolsky, and Nathan Rosen published a famous paper in which they showed that precise predictions are theoretically possible under certain circumstances. To do so, they considered two systems, A and B, in what is known as an “entangled” state, in which their properties are strongly correlated.
In this case, the results of measurements on system A can be used to predict the results of corresponding measurements on system B with arbitrary precision. This is possible even if systems A and B are spatially separated. The paradox is that an observer can use measurements on system A to make more precise statements about system B than an observer who has direct access to system B (but not to A).
thumbnail courtesy of phys.org