High-fives at a distance:

The [Haptoclone] system concentrates ultrasound energy at the intersections of the real and clone objects, which creates pressure to the real objects. If the “real object” is your finger, you feel contact force from the 3D clone object by the ultrasonic radiation pressure. At the same time, the same forces are applied to the original real object (of the clone) in the other workspace. The posture and the shape of the hand can be arbitrary. (Shinoda-Makino Lab)