From fun-house mirrors to holograms, we have all experienced incredible optical illusions. Right now, scientists are fascinated by the prospect of finding a way to perform an even more challenging trick: hiding things in plain sight.

We've made some metamaterials that have refractive indices that can redirect particular wavelengths of light. But one issue scientists have found particularly difficult to address is how to mask corners. Sharp corners are pretty common, and it's difficult to figure out ways to guide the surface waves of light around corners, as the light experiences scattering loss when encountering sharp corners. That's because there is a large mismatch in momentum of the light waves at the surface of an object before and after passing around the corner of an extremely compact shape.

Though scientists have successfully developed a few materials that can perform scattering-free guidance of surface waves around corners, these methods are limited. They rely on photonic crystals with a large magnetic response, which limits the types of waves it can influence.

When waves encounter a sharp corner, they pass through compact space, which causes the change in momentum (yes, photons have momentum). More advanced cloaking methods have focused on compensating for this change in momentum by curving the electromagnetic space in a way that tricks light waves into behaving as if they're moving in a straight line. Through this method, transformative optics has made strides towards developing a real invisibility cloak.

In the new work, scientists have demonstrated a way of bending surface light waves around sharp corners, one that works across a broad range of wavelengths, exhibiting almost ideal transmission. This method is able to bend the waves in a way that does not disturb other wave properties, such as the amplitude and phase. This could actually allow for the development of an invisibility cloak.

The scientists created bending adaptors that were essentially “corner cloaks”—able to hide corners as the waves traveled around them. Physically, the corner cloaks are triangular pieces that can be placed over a sharp corner. The cloaks are made of layered structures of subwavelength foam and ceramic materials that had a refractive index that's able to redirect light. Experimental results show that the cloaks almost completely conceal their presence from anyone looking at the light that passed through them.

It appears that the ultimate Harry Potter fantasy might be right around the corner for some of us.

PNAS, 2015. DOI: 10.1073/pnas.1508777112 (About DOIs).