Researchers have bent one of the most basic rules of quantum mechanics, a counterintuitive branch of physics that deals with atomic-scale interactions. Its "complementarity" rule asserts that it is impossible to observe light behaving as both a wave and a particle, though it is strictly both.
In an experiment reported in Science, researchers have now done exactly that. They say the feat "pulls back the veil" on quantum reality in a way that was thought to be prohibited by theory.
Quantum mechanics has spawned and continues to fuel spirited debates about the nature of what we can see and measure, and what nature keeps hidden - debates that often straddle the divide between the physical and the philosophical.
For instance, a well-known rule called the Heisenberg uncertainty principle maintains that for some pairs of measurements, high precision in one necessarily reduces the precision that can be achieved in the other. One embodiment of this idea lies in a "two-slit interferometer", in which light can pass through one of two slits and is viewed on a screen.
Let a number of the units of light called photons through the slits, and an interference pattern develops, like waves overlapping in a pond. However, keeping a close eye on which photons went through which slits - what may be termed a "strong measurement" - destroys the pattern. Read More