DOES quantum physics have no respect? Yet another law of classical physics 鈥� the diffraction limit 鈥� has been beaten by a trick that plays on the quantum properties of photons.
The principle of the diffraction limit means light cannot be used to see or inscribe features that are smaller than half its wavelength. This limits the density of data on a CD, for example, and the size of the circuits on microchips.
To get round this, physicists at the University of Toronto in Canada entangled three photons, a process which leaves them sharing the same quantum state. They then behave like a single photon with a wavelength only one-third as long. Using the photon group, the team made measurements three times finer than the diffraction limit should allow (Nature, vol 429, p 161).
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Other researchers have done similar things with two photons, but the three-photon measurement has taken years to master. 鈥淭hese entangled states don鈥檛 appear in nature. You have to work pretty hard to make them,鈥� explains team leader Jeff Lundeen.
They fired a pair of entangled photons and a lone photon from a laser simultaneously at opposite sides of a partially reflecting glass plate. The three photons became entangled only if they all ended up on the same path after encountering this obstacle. It is possible that the same technique could be used to create even bigger groups of entangled photons, allowing correspondingly smaller measurements.