From New Scientist [newscientist.com]
Ordinary crystals are three-dimensional objects whose atoms are arranged in regular, repeating patterns – just like table salt. They adopt this structure because it uses the lowest amount of energy possible to maintain.
Earlier this year, Frank Wilczek, a theoretical physicist at the Massachusetts Institute of Technology, speculated that a similar structure might repeat regularly in the fourth dimension – time.
Wilczek has also theorised that a working time crystal could be made into a computer, with different rotational states standing in for the 0s and 1s of a conventional computer.
The article includes a description (by Tongcang Li from the University of California, and others) of how such a time crystal could be built. Though it will be tricky because building the crystal will need temperatures close to absolute zero.
While Wilczek points out that the heat-death of the universe is, in principle, "very user friendly" for this kind of experiment because it would be cold and dark, there are other issues to consider.