Quote(Phys.org) —Is it possible that a moving object could have zero energy? The common sense answer is no, since motion itself is kinetic energy, but this answer has been challenged recently by the concept of quantum time crystals. First proposed in 2012 by the Nobel Laureate Frank Wilczek at MIT, quantum time crystals are theoretical systems that exhibit periodic oscillations in their ground state, i.e., their state of lowest possible energy.
Since then, researchers Tongcang Li et al., at the University of California, Berkeley, have proposed an experimental set-up of a time crystal based on charged particles (ions) in a ring-shaped ion trap. They argue that under a weak applied magnetic field, the ions should begin to rotate around the ion trap, and that, because the ions are in their ground state, their rotation theoretically would persist indefinitely.
But not everyone is embracing the concept of quantum time crystals. Physicist Patrick Bruno at the European Synchrotron Radiation Facility in Grenoble, France, has identified some holes in the concept and has proven a "no-go theorem" that rules out the possibility of spontaneous ground-state rotation for a broad class of systems that might be categorized as quantum time crystals.
Bruno's argument, which is published in a recent issue of Physical Review Letters, expands upon his Comment on Wilczek's original paper, both of which were published in Physical Review Letters in March.
According to Bruno's Comment, the quantum time crystal concept has two major flaws. First, the rotating soliton (a solitary wave pulse) that Wilczek describes in his model is not in its ground state, but rather in a higher energy state. Second, a system that displays rotational motion in its ground state is also able to radiate energy in the form of electromagnetic waves, which conflicts with the principle of energy conservation.
Wilczek previously responded to Bruno's first objection and acknowledged that the rotating soliton in his model was not in its ground state, but suggested that other models could be time crystals, i.e., possess a nonstationary ground state.
In the new paper, Bruno's proof demonstrates that setting a system of particles in motion around a one-dimensional magnetic ring always increases the ground-state energy of the system so that it's no longer in its ground state, which prohibits the existence of a rotating ground-state system. The proof covers systems rotating at any finite angular velocity. The argument builds upon Nobel Laureate Anthony Leggett's work on the rotational properties of superfluids.
Solitary
What would keep the magnetic ring at zero energy? It's not difficult to make a system in which one part is zero-energy, or exhibits perpetual motion, but we have to consider the entire system. Supplying energy to maintain the magnetic field, no matter how little, means that, as a system, it's not zero energy.