Multiple reflections like in a drop of paint
Inside a drop of paint, light is scattered so often that it seems impossible to demonstrate quantum effects. But despite the thousands of possible paths the light can take, researchers of the Uni of Twente now show that there are just 2 exits. Depending on the light pattern that enters the paint, 2 photons always come out through the same exit, or through different ones – as though they avoid each other.
Most of the experiments showing that light sometimes behaves like a wave and sometimes like a particle, are as simple as possible: a physics textbook example is Young’s two slit experiment. The number of possible light paths is limited, but even at this level, the experiments strongly challenge our intuition. According to the so-called ‘Hong-Ou-Mandel effect’, the photons come out through 1 of the 2 exits at the same time. Which one that will be, cannot be predicted beforehand.
The researchers succeed in this by programming the light in a very smart way. It is possible to influence scattering and interference inside the paint, limiting the number of exits to just two, even when there are thousands of possible paths.
Programming the incident light in a slightly different way, results in the opposite. The number of exits is still two. But if photon one leaves through one exit, photon two always leaves through the other. Which one will go through which exit is not known, but the photons always seem to avoid each other: a counterintuitive result again, because weak light pulses don’t ‘feel’ each other’s presence.
Controlling quantum light effects like in the new experiments, opens new possibilities in quantum computing and advanced security techniques like a ‘quantum credit card’. http://www.alphagalileo.org/ViewItem.aspx?ItemId=164038&CultureCode=en
http://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.053817
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