This crystal is the first quantum memory device of its kind that could fit on a chip alongside nano-sized instruments for detecting and sending signals written in quantum bits. The device iis only about 10 micrometers long and 0.7 micrometers wide — about as wide as a bacterial cell.
The secret to this storage device's tiny size is its shape, which resembles a Toblerone chocolate bar: a triangular prism with notches etched along the top.
Photons that enter the crystal at one end bounce back and forth between these "mirrors" a few thousand times before they can escape, which increases their likelihood of getting absorbed by an atom along the way. So the crystal's serrations helped it capture a decent number of photons despite its small number of atoms.