(ORDO NEWS) — A new phase of matter has been discovered in a quantum computer after physicists shone light on its qubits in a pattern inspired by the Fibonacci sequence.
If you think this is mind-blowing, then this strange quirk of quantum mechanics behaves as if it has two dimensions of time instead of one; this trait, the scientists say, makes the qubits more resilient, able to remain stable for the duration of the experiment.
This stability is called quantum coherence, and it is one of the main goals of an infallible quantum computer – and one of the most difficult to achieve.
According to computational quantum physicist Philip Dumitrescu of the Flatiron Institute, lead author of a new paper describing the phenomenon, the work represents “a completely different way of thinking about the phases of matter.”
“I’ve been working on these theoretical ideas for over five years, and it’s very exciting to see them put into practice in real life.”
Quantum computing is based on qubits, the quantum equivalent of computing bits. However, if bits process information in one of two states – 1 or 0, then qubits can be in both states at the same time – this state is known as quantum superposition.
The mathematical nature of this superposition can be incredibly powerful from a computational standpoint, allowing you to quickly solve problems under the right circumstances.
But the fuzzy, indeterminate nature of a series of qubits also depends on how their indeterminate states are connected to each other – this connection is called entanglement.
Unfortunately, qubits can become entangled with almost everything in their environment, introducing errors. The more subtle the blurry state of a qubit (or the more chaos in its environment), the greater the risk that it will lose coherence.
Improving coherence to the point of viability is likely a multitactic approach to removing a significant hurdle standing in the way of a functional quantum computer – every little bit counts.
“Even if you keep all the atoms under tight control, they can lose their quantumness by communicating with the environment, heating up or interacting with things in ways you didn’t plan,” explains Dumitrescu.
“In practice, experimental devices have many sources of errors that can degrade coherence after just a few laser pulses.”
Ensuring symmetry can be one of the means of protecting qubits from decoherence. Rotate an ordinary square ninety degrees and it will still remain the same shape. This symmetry protects it from certain rotational effects.
If you act on qubits with uniformly distributed laser pulses, then the symmetry will be based not on space, but on time. Dumitrescu and his colleagues wanted to see if this effect could be enhanced by adding not a symmetric periodicity, but an asymmetric quasi-periodicity.
According to their idea, this will add not one temporal symmetry, but two, one of which will actually be buried inside the other.
This idea was based on earlier work by the team, which proposed creating something called a quasi-crystal in time rather than space.
If a crystal consists of a symmetrical lattice of atoms repeating in space, like a square jungle or honeycomb lattice, then the pattern of atoms in a quasicrystal is non-repeating, like a Penrose tile, but still ordered.
The team ran their experiment on an advanced commercial quantum computer developed by quantum computing company Quantinuum.
This monster uses 10 ytterbium atoms (one of the elements used in atomic clocks) as qubits. These atoms are held in an electrical ion trap from which laser pulses can be used to control or measure.
Dumitrescu and his colleagues created a sequence of laser pulses based on Fibonacci numbers, where each segment is the sum of the previous two segments. The result is an ordered but non-repetitive sequence, similar to a quasi-crystal.
Quasicrystals can be mathematically described as segments of lower dimensional lattices of higher dimensional ones. The Penrose lattice can be described as a two-dimensional slice of a five-dimensional hypercube.
In the same way, laser command pulses can be described as a one-dimensional representation of a two-dimensional pattern. Theoretically, this means that it is potentially possible to impose two temporal symmetries on qubits.
The team tested their work by firing lasers at an array of ytterbium qubits, first in a symmetrical sequence and then quasi-periodically. They then measured the coherence of the two qubits at both ends of the trap.
With a periodic sequence, the qubits were stable for 1.5 seconds. For a quasi-periodic sequence, they remained stable for 5.5 seconds – the duration of the experiment.
The additional time symmetry, the researchers say, added another layer of protection against quantum decoherence.
“With this quasi-periodic sequence, a complex evolution takes place that cancels out all the errors that live on the edge,” Dumitrescu said.
“Because of this, the edge remains quantum mechanically coherent for much, much longer than one might expect.”
The work is not yet ready to be integrated into functional quantum computers, but it represents an important step towards that goal, the researchers say.
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