Just last month, physicists reported that they made the best case yet for why time crystals - hypothetical structures that have movement without presence of energy - could theoretically occur as physical objects. Physicists proposed the idea of time crystals about four years ago. And now researchers have managed to put a fourth dimension - the movement of time - to a crystal for the first time ever, giving it the capacity to act as a sort of everlasting 'time-keeper'.
These were proposed by Nobel-Prize winning theoretical physicist Frank Wilczek back in 2012, time crystals are proposed structures that seem to have movement even at their lowest energy state, called ground state. Crystals and magnets when in their ground state have puzzled the physicists for over a decade. At their ground state - they seem to break a fundamental law in physics called time-translation symmetry. These states were then called as asymmetrical ground states.
For anything to reach an asymmetrical ground state, it has to attain this asymmetry while standing still meaning no energy involved. So with this in mind, Wilczek suggested that it might be promising to generate an object that attains an asymmetrical ground state not through space like normal crystals or magnets - but across time.
What Wilczek envisioned was an object that could attain eternal movement while in its ground - or zero-energy - state by periodically switching amid states over and over again.
And now a group of physicists from the University of Maryland have tried out such an experiment, and they have finally achieved this.
As MIT Technology Review reports, in theory, the process is fairly simple - you just need to create a quantum system, where you 'hold onto' a bunch of ions in the shape of a ring, and then cool them to their lowest energy state.
Then you could see if the system breaks symmetry - the laws of physics predict that the ring will stay perfectly stationary with no energy for movement, but if time symmetry were broken at this ground state, then the ring could vary, or rotate, periodically in time.
Of course, it would never be possible to extract energy from this motion - that would violate the conservation of energy. But the temporal symmetry-breaking would manifest itself in this repeating motion in time, just as spatial symmetry-breaking manifests itself as repeating patterns in space.
If things were as simple as we just described, Wilczek would have built such a system back in 2012. But there’s just one problem - because quantum particles tend to blink in and out of positions in space, they aren’t influenced by time-dependent variables, meaning they don’t evolve over time.
The first step was for the University of Maryland to find a quantum system that was.
They did this by chaining together a line of ytterbium ions with spins that interact with each other, and holding them in an out-of-equilibrium state. This forced the quantum ions to become 'localised' in a specific space, and therefore influenced by time.
Using a laser, the team could then start changing the spin of specific ytterbium ions, and by flipping the spin of one ion, it caused the next one to flip, and so on down the chain, until every ion was oscillating.
Once the laser had been used to set the first one off, the oscillation was perpetual, and over time, the researchers noticed something strange.
As Tech Review explains:
These guys discovered that after allowing the system to evolve, the interactions occurred at a rate that was twice the original period. Since there is no driving force with that period, the only explanation is that the time symmetry must have been broken, thereby allowing these longer periods. In other words, [they] had created a time crystal.
To be clear, we’re not talking about perpetual motion machines here, because by definition, there is no energy in these systems.
But it does demonstrate that time crystals can occur in a real, physical system, and the team says that they could help us solve the problem of quantum memory - that is, how to retain information in the future generation of quantum computers.
The researchers have submitted their results to the pre-print website arXiv.org, to be picked over by their physicist peers, so we'll have to wait and see if their experiment can be independently replicated. But if it can, we're only just beginning to realise the potential of the incredibly strange time crystal.