Qubits can spin in two dimensions, instead of just one, and it could be revolutionary for quantum computing.
In new research, scientists have trained atoms to exhibit two forms of time at the same, well, time. While the phenomenon is not bending time away from what you’d expect looking at the clock, the matter shows behaviors from two different time modes, giving it special properties. Scientists believe this odd, double-time phenomenon could represent a new phase of matter.
Researchers from a few American universities, as well as Honeywell quantum-computing spinoff Quantinuum, collaborated on the new paper, which appeared late last month in the journal Nature. The experimental setup is made up of lasers and ytterbium atoms. Ytterbium is a metallic element whose arrangement of electrons makes it unusually suited to respond to laser treatments in a particular area of the wave spectrum. To trigger the new “dynamical topological phase,” scientists first hold ytterbium atoms in place using an electric ion field—like a tiny magnet—then bombard them with the right wavelength of laser to supercool the ytterbium.
Broomfield, Colorado-based Quantinuum studies a particular quantum computer that’s made of ten ytterbium atoms in a shared system. It’s these ten atoms, held by the electric fields mentioned above, that do the computing. A group of atoms can be entangled— meaning they’re intrinsically linked into a group that acts as one piece, despite being ten separate pieces. And within that, individual atoms can be tuned to reflect different information.
Think of how we write numbers. In binary, the largest ten-digit number is 1111111111, and that’s just 1,023 total. But you can write ten digits in base 10, our usual counting numbers, and get 9,999,999,999. That’s accomplished by simply increasing the number of possibilities that each digit can dial to from (0, 1) all the way up to to (0, 1, . . . . 8, 9). So what about a system where, theoretically, each of ten atoms could be positioned anywhere on the dial?
If that sounds amazing, you’re not wrong! There are multiple reasons why scientists and industry speculators around the world are watching the field of quantum computers with bated breath. But there’s still a very big catch, and that’s where this research comes in. The atoms in the quantum computer, known as quantum bits, or qubits, are really vulnerable, because we don’t yet have a great way to keep them in the quantum state for long.
That’s because of the observer principle in quantum physics: measuring a particle in a quantum state changes, and can even destroy, the quantum state. In this case, that means unhooking all the atoms from the shared yoke of entanglement. And even worse, the “observer” can be anything happening in the complex soup of air and forces and particles all around the quantum computer.
Back to the new experiment. While the ten atoms are in an entangled state, they’re fragile, and need to be more stable. Enter three of the scientists from this research team. In 2018, they theorized that that they could train the ytterbium atoms to kind of exist in two flows of time at once. They took inspiration from the Fibonacci sequence. In math, it’s a sequence of integers that starts with zero and follows a simple rule: that each number is equal to the sum of the previous two numbers. The beginning of the sequence would be 0, 1, 1, 2, 3, 5, 8, etc. The team pulsed the atoms with lasers that alternated in a pattern similar to the Fibonacci sequence, where the repetition of pulses grows by including pieces that came before. But, critically, no piece fully repeats.
By alternating pulses in this way, they created a quasicrystal, a term for a pattern that is not as regular or repeating as a true crystal, but that has many of the same qualities. The quasi-crystal occurs in two dimensions, by including both the idea of an alternating pulse and also a “magnitude” of the pulse pattern from the Fibonacci sequence, like an (x, y) plot of lines. Those two dimensions each come with their own version of the flow of time. And both are flattened, and included, in the single dimension of just one laser pulsing on and off.
Having the extra “support” of an added, virtual dimension of time helps to make the quantum computer a lot more stable, the researchers have confirmed four years after first theorizing it. That’s because instead of just one mode of time symmetry, something introduced by a rhythmic pulsing of lasers, this system has two modes. Like a throat singer, it’s “resonating” in two different patterns at the same time.
The results of this experiment really speak for themselves. With the traditional, single-mode laser blasts, the quantum computer stayed in the quantum state for 1.5 seconds, which is high for this kind of test. But when the researchers switched on the Fibonacci-inspired quasicrystal pulses, the system stayed in the quantum state for 5.5 seconds—a lifetime in quantum computing.
Quantinuum and its researchers are excited about the finding, but there is still a lot of work to be done. Next for them will be finding a way to merge this technology with a quantum computing system that is actually doing some computing. Hopefully, the increased stability will help support the system while its qubits are vulnerable to the observer effect.