We might finally know what time crystals are good for: Nobel Prize possible (Patreon)

[This is a transcript with links to references.]

Time Crystals sounds  like something from Hogwarts,  but it’s actually solid-state physics. Maybe not quite as mysterious as the name suggests, but nonetheless interesting. A team of physicists has now built the most robust time crystal ever and even figured out what these things could be good for. Let’s have a look.

A normal crystal is a regular configuration of atoms that repeats in each direction in space. A time crystal is a configuration of atoms that repeats both in space and in time. It oscillates, basically, but the funny thing is that it’s not a type of oscillation anyone expected or even thought of. Except for Frank Wilczek,  who proposed time crystals in 2012.

Wilczek has already won one Nobel prize and he is on a very promising track for a second one, either with the time crystals or with axions,  that are a type of dark matter particles which experiments are looking for all over the globe.

But today’s topic is not dark matter,  it’s time crystals. Can we agree that physicists, if nothing else, have at least the coolest terminology?

Time crystals are a new type of self-organization in solids basically. They oscillate kind of like some chemical reactions can, surprisingly enough, oscillate.

Unfortunately, in physics it doesn’t look as impressive as in chemistry. I’ve really studied the wrong field to end up on YouTube.

 Wilczek’s original idea was that some materials could oscillate all on their own, but it turned out that this isn’t compatible with energy conservation.  The material needs to be supplied with energy.

But a few years after Wilczek proposed the idea, the first experiments managed to create the time crystals for real.  In such experiments the energy is typically supplied by shooting with a laser at some kind of material. Some materials then begin some sort of oscillation in response. This oscillation can even continue after the lasers are turned off.

Now, if you poke a material with a periodic oscillation  and you get a periodic response, that’s nice but kinda unsurprising.  If I periodically complain about particle physicists, also get periodic responses. However, you can also create time crystals if the energy that you supply doesn’t generate a beat on its own.  This is then called a “continuous time crystal” and this is also what they did in this new work. A continuous time crystal has its own internal periodicity.

Continuous time crystalshave previously been generated in clouds of ultra-cold atoms,  for example in 2022 by researchers in Hamburg, Germany. These clouds are typically made of a few ten thousand atoms.

When the atoms are cooled to near zero, they create what is called a Bose-Einstein condensate. Yes, this guy again.

If the cloud of atoms is cold enough to form a Bose-Einstein condensate,  this means it has quantum properties throughout. This means in particular it can behave like both a particle and a wave.  The researchers then supply it with energy from electromagnetic waves and it responded! In this example they saw an oscillation in the number density at a frequency of a few milliseconds, nothing to do with the frequency of the radiation. So, a time crystal.

What makes these time crystals  so interesting is that they display an entirely new physical phenomenon.  Honestly, I think at the moment physicists don’t really know what it’s good for.  There’s been some talk about using it for quantum computing,  but I can’t really see how this would work. Timekeeping is a possibility.  Because every time you have something that reliably oscillates you can use that as a pacemaker.

But we already have highly reliable atomic clocks  and a cloud of atoms cooled to some milli Kelvin isn’t going to revolutionize wristwatches, especially not if these things oscillate barely a few milliseconds.

And this then brings me to the new paper. In this experiment, researchers from the technical university in Dortmund, Germany managed to produce a time crystal that lasted a full 40 minutes.  That’s more than a million times longer than the previous ones. Quite an achievement!

For this, they used a semiconductor made from indium   gallium arsenide doped with silicon, at a temperature of about six degrees above absolute zero. Then they shot at it with a laser. The material’s spin states began to oscillate at a period of about 6 seconds.  So it’s not like the oscillation is in a deformation of the material, it’s a periodic back and forth of the spins.

I know this sounds somewhat academic, but I find this totally fascinating. It’s just not what you expect a semiconductor to do. And that oscillation was remarkably stable, as you can see in this figure.

They also noticed that the oscillation period is very sensitive to changes in the magnetic field  and temperature.  For this reason, they suggest that such materials might one day come in handy as sensors in which one could infer changes in the magnetic field or temperature from the oscillation frequency.

I am not joking when I say Frank Wilczek  might well end up winning another Nobel Prize. You see, it was a similar story with topological insulators.  Those are materials with unique electric properties,  for example they might only conduct electricity on the surface but not in the bulk. The idea came out of theoretical work by Thouless, Haldane, and Kosterlitz about 25 years ago.

At first no one had any idea what it might be good for, just like today with the time crystals.  But in 2016, they won the Nobel Prize because by then their idea had found applications in some types of high speed electronics. So it might well be that time crystals will soon find an application, and Wilczek is up for another Nobel Prize.