This strange new phase of matter seems to span 2 time dimensions.


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A new phase of matter has been discovered in a quantum computer after physicists beamed light at its qubits in a pattern inspired by the Fibonacci sequence.

If you think it’s mind-boggling, this strange quirk of quantum mechanics behaves as if it has two time dimensions instead of one; this trait, the scientists say, makes the qubits more robust, able to remain stable throughout an experiment.

This stability is called quantum coherence, and it’s one of the main goals of an infallible quantum computer—and one of the hardest to achieve.

The work is “a completely different way of thinking about the phases of matter,” according to computational physicist Philippe Dumitrescu of the Flatiron Institute, lead author of a new paper describing the phenomenon.

“I have been working on these theoretical ideas for more than five years, and it is very interesting to see how they are actually implemented in experiments.”

Quantum computing is based on qubits, the quantum equivalent of computing bits. However, when bits process information in one of two states, 1 or 0, qubits can be in both at the same time, a state known as quantum superposition.

The mathematical nature of this superposition can be incredibly powerful from a computational standpoint, being able to solve problems quickly under the right circumstances.

But the fuzzy, undefined nature of a series of qubits also depends on how their undefined states relate to each other, a relationship called entanglement.

Unfortunately, qubits can get entangled with just about anything in their environment, introducing errors. The more delicate the blurred state of a qubit (or the more chaos in its environment), the higher the risk of it losing this coherence.

Improving consistency to the point of viability is likely a multitactic approach to removing a major hurdle standing in the way of a functional quantum computer—every little thing counts.

“Even if you keep all the atoms under tight control, they can lose their quantumness by talking to the environment, heating up or interacting with things differently than you planned,” Dumitrescu explained.

“In practice, experimental devices have many sources of errors that can degrade coherence after just a few laser pulses.”

Ensuring symmetry can be one way to protect qubits from decoherence. Rotate the good old square ninety degrees and it will still have the same shape. This symmetry protects it from some rotational effects.

Exposing the qubits to uniformly distributed laser pulses guarantees a symmetry based not on space, but on time. Dumitrescu and his colleagues wanted to see if they could enhance this effect by adding not symmetric periodicity, but asymmetric quasi-periodicity.

They suggested that this would add not one temporal symmetry, but two; one is effectively hidden inside the other.

The idea was based on earlier work by the group, which proposed creating something called a quasi-crystal in time rather than space. If a crystal consists of a symmetrical lattice of atoms that repeats in space, like a square grid in a gym or a honeycomb, then the pattern of atoms on a quasicrystal is non-repeating, like a Penrose tiling, but still ordered.

The team ran their experiment on an advanced commercial quantum computer developed by Quantinuum, a quantum computing company. This beast uses 10 ytterbium atoms (one of the preferred elements for atomic clocks) for its qubits. These atoms are held in an electrical ion trap from which laser pulses can be used to control or measure them.

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 a sequence that is ordered but not repeated, as in a quasicrystal.

Quasicrystals can be mathematically described as low-dimensional segments of multidimensional lattices. A Penrose tiling can be described as a two-dimensional slice of a five-dimensional hypercube.

Similarly, the team’s laser pulses can be described as a one-dimensional representation of a two-dimensional pattern. Theoretically, this meant that he could potentially impose two temporal symmetries on qubits.

The team tested their work by flashing lasers on 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.

For 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 extra temporal symmetry added another layer of protection against quantum decoherence, the researchers say.

“With this quasi-periodic sequence, a complex evolution occurs that eliminates all the errors living on the edge,” said Dumitrescu.

“Because of this, the edge remains quantum mechanically coherent for much, much longer than you would 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 said.

The study was published in Nature.

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