Areas of intense ultrasound waves (red) alternately squeeze and stretch a thin film 100 million times a second. This squeezing and stretching takes place over a very small area – the picture is about the width of a single strand of hair.

Squeezing and stretching materials only a few atoms thick can result in dramatic changes. A non-magnet can sometimes transform to a magnet when squeezed hard enough, or a stretched superconductor can transform to a non-superconductor.  We can use this to rapidly change a material between two states.