“This was a global race. Together with Google, we were the first to cross the finish line,” says researcher Tim Taminiau of QuTech about the time crystal that he built with colleagues in the lab of research institute QuTech in Delft and those of their competitors at tech giant Google in the United States. Both crystals also have their own scoop. “Google’s is the largest — it’s made up of twice as many qubits — and ours lives about ten times longer.”
That sounds special, but… time crystals? Qubits? Just as you shouldn’t start a marathon without warming up, it’s also better to take a small step back before we enter the most advanced front of modern physics.
Whether it’s a sparkling diamond or an ordinary grain of table salt, look deep within them and you will discover a serene order. Far beyond the human scale, a factor ten thousand smaller than a coronavirus, you enter the world of atoms, the building blocks of everything around us. In crystals such as diamond and salt, all those atoms are arranged in a neat grid with the same distance between each particle – a crystal lattice. ‘Ordinary’ crystals are thus essentially space crystals, arranged in the three spatial dimensions: top/bottom, left/right, front/back.
Like the hands of a clock
In the world of physics people are accustomed not to think in three dimensions, but in four. It also includes a dimension of time: earlier/later. It is therefore not surprising that in 2012, physicist and Nobel Prize winner Frank Wilczek, while he was lecturing on ‘ordinary’ crystals, suddenly thought: is this not possible in time?
In time crystals, particles would not have regular positions, but show regular behavior over time. They would move and return to their initial state after a fixed period of time. Just like the hands of a clock: after 12 o’clock they are in exactly the same place again.
But a clock is not a time crystal. To keep it running you have to continuously put energy into it. A battery, a radar that you have to turn on now and then, a plug in a socket – it won’t work without it. Wilczek’s time crystals don’t need that. “They would keep moving forever, without you having to add energy to them,” Taminiau says.
Eternal movement, without costing energy? That smacks of perpetuum mobile, a wandering technology that is especially popular among attic room inventors: a machine that keeps moving forever and with which you can crank other machines. A free perpetual energy source. This is impossible with Wilczek’s time crystals, says Taminiau. ‘No energy goes in, but it doesn’t come out either.’
Despite this, alarm bells went off among many physicists after Wilczek and colleague Alfred Shapere published the idea in 2012 in physics sheet Physical Review Letters. In 2014, therefore, followed the rebuttal, published in the same magazine: time crystals could never exist.
Influence from outside
Until another research group accidentally discovered one yet. Their ‘pi spin-glass phase’, as they originally called it, turned out to be a time crystal on closer inspection. The basic ingredient? A row of linked qubits, a variant of the ‘regular’ bit, the zeros and ones of information. They described how such qubits could flip when you shine a laser on them: ‘001010’ then suddenly becomes ‘110101’, for example. This reversal shows a fixed period, and – importantly – the qubits consume no net energy from the laser beam. So, so to speak, they are not plugged in. Together they form a time crystal that, as long as the laser is on, moves like a clock that ticks eternally: 001010, *tick* 110101, *tak* 001010, *tick* 110101, *tak* 001010, ad infinitum.
The conclusion: unlike ‘normal’ crystals, time crystals never arise spontaneously. You need something, an outside influence, a laser beam, or something similar. You have to make them.
The row of connected qubits from 2016 was theoretically improved and eventually too built in the lab, but that still did not constitute definitive evidence for time crystals. They could also be something else that — if you let the experiment run long enough — would stop moving on its own.
The only question was: how do you see the difference? Real time crystals will also die out in the lab after a while. In that case, not for fundamental reasons, but because such an experiment always leaks energy to the outside world. Via a detour, both Google and QuTech were able to prove that they had built a real crystal.
Philosophical Impact
QuTech and Google use their quantum computers for this, the predecessors of a calculation beast that can solve certain sums much faster. Some experts dream, among other things, that those computers can design medicines specifically tailored to the individual, or materials that can solve the energy problem. “This demonstrates how you can use such a quantum computer in a new way,” said Gabriel Perdue of the American Fermilab, who was not involved in the research himself. against magazine Popular Science.
Race concluded, time crystal built…now what? ‘What we can do with this is an open question,’ says Taminiau. There are ideas: time crystals may be useful for building better quantum computers, or as very sensitive sensors. ‘But what is more important is what we learn from this about how nature works.’
And then there is the philosophical impact. Where physicists have been sweeping space and time for decades, everyone knows that there must actually be a difference. ‘After all, you can go backwards through space, but not back in time’, says Taminiau. The fact that time crystals, unlike the normal variants, do not arise in nature illustrates that difference. “This teaches us something about the deeper relationship between space and time.”