Photon transmission through sub-wavelength diameter apertures Delft | Optica In Optics Express 16, 10 (abstract, full article) and concurrent TU Delft summary, Photonics review, Adam, Planken et al. report on high time-resolution terahertz mapping of photon transmission through sub-wavelength diameter apertures:
"According to the laws of physics, it is particularly difficult to pass light through a hole smaller than half the wavelength of the light used." The Delft group conducted experiments using extremely high time-resolution measurements in the terahertz (THz) frequency range. The group discovered that even if the hole is up to fifty times smaller than the wavelength used, sufficient light can pass through to allow measurements near the hole – an extremely difficult task using other methods. "Improving the sharpness of THz microscopes, coupled with more sensitive detectors, will improve the viability of creating images of biological cells using this type of measurement."
Prior experiments at Leiden University (Nature 418, 304-306) have also studied photon transmission through sub-wavelength metal films and shown entanglement conservation to be much more robust than expected – surviving the conversion process from surface-plasmon waves, which tunnel through the barrier, before reradiating as photons on the opposite side of the film. "It's a good omen, because it's saying quantum entanglement can survive when you might not expect it to," says Bill Barnes, a photonics expert at the University of Exeter. "If they can survive this, what else can they survive?"