By making a strange kind of particle that is its own antiparticle out of a time crystal, physicists aim to develop a quantum computer that’s not only more reliable, but far more lightweight than anything currently in the pipeline.
Time crystals and quasiparticles called Majorana fermions have made headlines in recent years thanks to the fact they’re both so incredibly weird. So putting them together to make a quantum computer sounds like the perfect marriage.
The theoretical union of these fascinating phenomena was proposed by physicists from the National University of Singapore, who recognised similarities between them that could be exploited in what’s known as a topological quantum computer.
There’s enough jargon here to fill an entire Star Trek episode, so we’ll need to pull them apart before looking at why this is such an interesting idea.
First of all, time crystals resemble regular old crystals in that they are based on repeating units. Rather than being stretched out across three dimensions of space, these ones are repeated over time.
The really odd thing is this resonance in the movements of particles doesn’t rely on a constant energy source. But before you scream ‘perpetual motion machine’, time crystals can’t be tapped as a supply of free energy, so they don’t break any rules.
Still, that ‘ticking’ could play a role in storing information by turning them into what the physicists call ‘magic states’.
Which is where Majorana fermions come into play.
Proposed around 80 years ago by the theoretical physicist Enrico Majorana, these hypothetical elementary particles are their own antiparticle.
Specifically, they are a type of fermion – particles that are technically categorised as possessing a half spin. To most of us unfamiliar with technicalities, they are the chunky stuff making up atoms.
In spite of nearly a century of looking, we’ve failed to come up with one of Enrico’s special two-in-one particles in the wild. But we do have the next best thing – electrons working together in such a way that their collective behaviour produces something just like a Majorana fermion.
Majorana fermions – or rather, their quasiparticle doppelgangers – can be made to move in a rather unique twisting fashion as they shoot down a conductor. This ‘braid’ motion makes them a perfect candidate for a topological version of a quantum computer.
Where your run-of-the-mill quantum machine relies the undecided state of a particle – such as its potential spin – to form its key component, a topological quantum computer instead uses those twisting braids.
“Loosely speaking, braiding refers to exchanging the location of two particles,” physicist Jiangbin Gong told Phys.org.
“We know in real life that there are different types of braids, and that converting one braid to another requires certain operations that nature cannot do by itself.”
Braids don’t suffer the same kind of fragility as other quantum states, making them attractive as the basis of quantum computing. The trick is to harness those Majorana fermions in such a way as to build a working device.
Researchers have covered some solid ground in recent years, but we’re still some way off seeing them become a competitive choice.
Making those twisting Majorana fermions from time crystals could provide a tantalising new option.
The researchers modelled the behaviour of a lattice of particles behaving as a time crystal as they sent electrons down their edge in the form of Majorana quasiparticles.
Manipulating those special particles made them act just like they were braiding, allowing for states that that could be the foundation of operations in a universal quantum computer.
“Braiding time crystals is potentially useful for quantum computation because we exploit their time-domain features and thus obtain more qubits for encoding information,” says Gong.
More qubits equals less hardware, which coupled with a less error-prone process makes these time-crystal topological quantum computers look pretty appealing.
The next step for the researchers is to explore the ways they can ramp up the process, moving braids into an array of wires to create more intricate patterns.
We hope this will be one fruitful, if weird, marriage.
This research was published in Physical Review Letters.