Figure 2
Phys. Rev. Lett. 106 120602 (2011)

Boxed in. In computer simulations of waves in a box, when selecting only for waves with high transmission from upper left to lower right, the results can be somewhat chaotic (top). But a new procedure for selecting waves with particle-like trajectories can generate waves that go from A to B without eavesdropper E being able to intercept the signal.