An experimental design for creating a space-time crystal has been proposed by scientists at Berkeley Lab, based on an electric-field ion trap and the Coulomb repulsion of particles that carry that same electrical charge.
A space-time crystal is a four-dimensional crystal that has periodic structure in time as well as space. It is a clock that could keep perfect time forever, even after the heat death of the universe.
“The electric field of the ion trap holds charged particles in place and Coulomb repulsion causes them to spontaneously form a spatial ring crystal,” said Xiang Zhang, lead researcher.
The method could have applications in studying how complex physical properties and behaviours emerge from collective interactions of large numbers of individual particles. It would also be useful for studying quantum phenomena, such as entanglement: the action of one particle impacting another, even if they are separated by vast distances.
“Under the application of a weak static magnetic field, the ring-shaped ion crystal will begin a rotation that will never stop. The persistent rotation of trapped ions produces temporal order, leading to the formation of a space-time crystal at the lowest quantum energy state,” Zhang explained.
The space-time crystal is already at its lowest quantum energy state, and therefore, its temporal order (timekeeping) will theoretically persist even after the rest of the universe reaches entropy.
Crystallization takes place when heat is removed from a molecular system until it reaches its lower energy state. At certain points of lower energy, continuous spatial symmetry breaks down and the crystal assumes discrete symmetry, meaning that instead of the structure being the same in all directions, it is the same in only a few.
Just as a 3D crystal is configured at the lowest quantum energy state when continuous spatial symmetry is broken into discrete symmetry, so too should symmetry-breaking configure the space-time crystal’s temporal component.
A spatial ring of trapped ions in persistent rotation would periodically reproduce itself in time, forming a temporal analog of an ordinary spatial crystal.
“These analogs could open doors to fundamentally new technologies and devices for a variety of applications,” Zhang added.