The classic double-slit experiment of quantum physics involves shining light through two narrow gaps to show that it can behave as a wave 鈥� now it seems the slits can be entirely replaced by a single atom.
The double-slit experiment dates to the 1800s. When light is shined through two adjacent narrow slits and onto a screen, it forms a pattern of stripes. This is the result of light behaving like a wave, with ripples from the two slits both boosting and cancelling each other out. Light can also behave like a particle, and the double-slit experiment was key for establishing the waviness of its nature.
A hundred years later, as physicists were becoming increasingly good at shaping light by making it interact with matter, two Nobel laureates, Claude Cohen-Tannoudji and Alain Aspect, along with their colleagues, investigated a radically small set-up for the double-slit phenomenon 鈥� a single atom and no slits at all.
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Their initial calculations suggested that light would get too entangled with the atom to be able to clash with itself and create the stripes, but now Hao Zhang at the China Academy of Engineering Physics and his colleagues have come up with a scenario that could challenge this argument.
The researchers looked at a situation where a single atom nearly as cold as absolute zero would be positioned between three mirrors. The mirrors form a reflective cavity where any light gets stuck in an endless back-and-forth bounce. The atom itself would be trapped in one of two deep 鈥渆nergy wells鈥�, a situation analogous to a ball sitting at the bottom of one of two adjacent holes in the ground. Such a ball would have to stay where it is, but the atom can undergo a process called quantum tunnelling to periodically move between the two wells.
The researchers calculated that if the reflective cavity was filled with light, the light would interact with the atom at each step of its tunnelling motion and these repeated interactions would replicate the double-slit effect.
鈥淲hether you could do this with a single atom was a fundamental question that people asked a long time ago and gave a negative answer, which is a little boring,鈥� says Zhang. 鈥淲e reformulated it and could get a great signal with very realistic experimental numbers,鈥� he says. His team has already built the set-up for the experiment and hopes to complete it in the near future, so it was important to prove that the numbers could work, he says.
The researchers think this could make their set-up useful as a component of quantum communication networks or a part of devices for very precise measurements of quantum fields.
Journal reference:
Physical Review A,
