For the first time in the history of science, a group of physicists from Finland and Great Britain managed to force two isolated groups of particles to interact in a unique state of matter called a space-time crystal. And these interacting crystals formed a single evolving system, which in the future can be used in practice in the field of quantum computing and quantum communications.
We remind our readers that the possibility of the existence of space-time crystals was theoretically substantiated in 2012 by Frank Wilczek, a physicist at the Massachusetts Institute of Technology. For some time it was believed that these crystals were impossible, until in 2016 one of the groups of physicists managed to create such a crystal experimentally.
In ordinary crystals, atoms are ordered in the form of a crystal lattice, the structure of which is repeated in three-dimensional space in any direction. Space-time crystals also have an ordered three-dimensional structure, but all the particles of these crystals are constantly moving so that at certain intervals the structure of the crystal is repeated. Moreover, the movement of the particles that make up space-time crystals cannot be associated with any external influence. These crystals vibrate only at one strictly defined frequency.
The frequency stability of space-time crystals is determined by the fact that they are always in the lowest energy state, called the standard state. In this state, there is no excess energy inside the crystal that can disturb the harmony of endless movement and vibrations.
The space-time crystals that scientists have worked with are made up of quasi-particles called magnons. And magnons, in turn, are collective perturbations of electron spins that can propagate through the crystal lattice, like waves.
Magnons are created when helium-3, a stable isotope of helium with two protons and one neutron, is cooled to a temperature one thousandth of a degree above absolute zero. At this temperature, helium turns into a superfluid liquid (superfluid) having zero viscosity and capable of flowing without resistance.
Next, the scientists organized two clouds of Bose-Einstein condensate, each of which consisted of about a trillion magnon quasi-particles. At the same time, each condensate cloud acquired a certain density, passed into the lowest energy state and began to act like one huge quasi-particle, and individual magnon quasi-particles inside the condensate cloud began an endless "dance", forming a space-time crystal.
When the scientists allowed the two space-time crystals to touch each other, they exchanged a certain amount of magnons, which immediately affected the vibrations of both crystals. After such an exchange, the crystals became interconnected and formed a single system capable of being in one of two discrete states.
It is quite natural that some of the scientists consider space-time crystals as candidates for the role of qubits, quantum bits, which are the basis of quantum computing systems. Such "crystalline" qubits will have high stability, and the creation of a system of two coupled qubit crystals opens up generally fantastic prospects in the field of quantum computing. Moreover, other groups of scientists not so long ago managed to create space-time crystals that exist and function at room temperature, which do not require ultra-low temperatures and thorough isolation from the environment.
In their further research, scientists plan to implement more complex types of interactions between space-time crystals, develop precise methods for controlling the parameters of interactions and the energy state of crystals. And, if they manage to realize all their ideas, then this can lead to real breakthroughs in the field of practical use of space-time crystals.