Feuer Frei!
06-05-11, 05:22 AM
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 (http://www.sciencemag.org/content/332/6034/1170.abstract), 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.
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.
Now, Aephraim Steinberg of the University of Toronto and his colleagues have sidestepped this limitation by undertaking "weak measurements" of the photons' momentum.
The team allowed the photons to pass through a thin sliver of the mineral calcite which gave each photon a tiny nudge in its path, with the amount of deviation dependent on which slit it passed through.
By averaging over a great many photons passing through the apparatus, and only measuring the light patterns on a camera, the team was able to infer what paths the photons had taken.
A central idea in quantum mechanics is that light and matter can behave as both particle and wave
However, the idea of "complementarity" prevents observation of both behaviours simultaneously
In the two-slit experiment, light is passed through two tiny holes and is then viewed on a screen
The two beams interfere with each other, forming a rippled "diffraction pattern" - as if the light were made of a number of waves adding or cancelling
However, if one of the holes is blocked, the light can be seen as a single beam on the screen - as if light were made of particles
The new work, for the first time, observes both kinds of behaviour at the same time
SOURCE (http://www.bbc.co.uk/news/science-environment-13626587)
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 (http://www.sciencemag.org/content/332/6034/1170.abstract), 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.
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.
Now, Aephraim Steinberg of the University of Toronto and his colleagues have sidestepped this limitation by undertaking "weak measurements" of the photons' momentum.
The team allowed the photons to pass through a thin sliver of the mineral calcite which gave each photon a tiny nudge in its path, with the amount of deviation dependent on which slit it passed through.
By averaging over a great many photons passing through the apparatus, and only measuring the light patterns on a camera, the team was able to infer what paths the photons had taken.
A central idea in quantum mechanics is that light and matter can behave as both particle and wave
However, the idea of "complementarity" prevents observation of both behaviours simultaneously
In the two-slit experiment, light is passed through two tiny holes and is then viewed on a screen
The two beams interfere with each other, forming a rippled "diffraction pattern" - as if the light were made of a number of waves adding or cancelling
However, if one of the holes is blocked, the light can be seen as a single beam on the screen - as if light were made of particles
The new work, for the first time, observes both kinds of behaviour at the same time
SOURCE (http://www.bbc.co.uk/news/science-environment-13626587)