Confining classical and quantum waves with crystals

Manipulating elusive waves like light, sound or electrons, in periodic structures or crystals, has something mysterious. In the leading physics journal Physical Review Letters, published by the American Physical Society, a team of researchers from the University of Twente now describes how any kind of wave, whether quantum or classical, is confined in any kind of crystal. The results will notably boost efficient new integrated circuits that steer information encoded in tiny light pulses through smart cities. Waves represent an inseparable part of our everyday life, whether we listen to music, observe our reflection in a mirror, or experience the ocean rocking a sailing ship. A central challenge in manipulating waves for applications requires the ability to confine the waves in small regions in space. Scientists already know that it's possible by deliberately introducing tailored deviations from perfect periodicity into the crystal. But how exactly are the waves locked up? Are they confined in all dimensions simultaneously, or do they retain the freedom to move along a line or in a plane? Remarkably, the key step from having the crystal's structure to predicting the confinement of waves had not been taken until now.