Physics and Technology Forefronts

Photonic Crystals considered by some to be "electromagnetic crystals".

"Photonic crystals are the electromagnetic analog of semiconductor crystals. They are artificial crystal structures that do for electromagnetic waves what semiconductor crystals do for electron waves. In today's world, electronic semiconductors are the basis for the micro-electronic, telecommunications, and computer industries. We are just now beginning to understand the exciting potential of their electromagnetic cousins for tomorrow's world."

I traveled down an interesting rabbit hole, today. Creating electormagnetic crystals is not new research (no later than 2002), however it is the first time I have have happened upon it, because of looking for information about Danish Physicist Lene Hau. She and her teammates seem to have been the first to produce Bose-Einstein Condensate "which eventually formed in June 1997 after Hau and her teammates successfully cooled the atoms."

from Britannica
"Bose-Einstein condensate (BEC), a state of matter in which separate atoms or subatomic particles, cooled to near absolute zero (0 K, − 273.15 °C, or − 459.67 °F; K = kelvin), coalesce into a single quantum mechanical entity—that is, one that can be described by a wave function—on a near-macroscopic scale."

Apparently not long after they were able to slow down the speed of light by the use of Bose-Einstein Condensate (considered to be the 5th state of matter) eventually to stop light (photons, individual photons). What value manipulating individual photons has, is no mentioned anywhere I have looked.

As of 2022 it is considered there are seven states of matter: gases, liquids, solids, ionized plasmas, quark-gluon plasma (apparently debatable), Bose-Einstein Condensates (now the 6th state) and Fermionic Condensates.

The more one learns, the more there is to learn - as usual!