informatics

Technological Innovation Website Editor – 07/21/2022

In this quantum processor, physicists have created a never-before-seen phase of matter that acts as if time has two dimensions.

[Imagem: Quantinuum]

**two dimensions of time**

Firing a sequence of Fibonacci-inspired laser pulses toward the qubits of a quantum computer, physicists created two dimensions of time, yet there was still only a single stream of time running.

And this almost wacky phenomenon brings a long-sought benefit: The information stored in this “second time” is much better protected from errors than the alternative configurations currently used to protect quantum computers from errors.

In other words, the information in the qubits stays undistorted much longer because they take advantage of the fact that they can stay in one or the other of the temporal dimensions.

Using an extra time dimension “is a completely different way of thinking about the phases of matter. I’ve been working on these theoretical ideas for over five years, and seeing them come to fruition in experiments is exciting,” said Philipp Dumitrescu, who developed this new approach with colleagues in Canada and the US.

**Multiple data and no data**

Error correction is one of the biggest challenges in quantum computing because the same phenomenon that gives qubits superpowers makes them extremely vulnerable to any environmental interference – this is one of the reasons why today’s quantum computers are kept close to absolute zero inside microwave refrigerators. dilution.

While an ordinary electronic bit can take on the values 0 or 1, a qubit can be 0, 1, or anything else in between, thanks to a phenomenon called superposition. This is the same phenomenon at the basis of Schrodinger’s well-known thought experiment, in which a cat is both alive and dead at the same time, only deciding when the box it is open in – the opening of the box actually represents the reading of a quantum state. superposition, which is the same thing that is done every time a qubit is read.

[Imagem: Domnio Pblico]

The most typically used qubits are atoms, which are read using lasers – and the light photons themselves that read them interact with them, which makes everything very error-prone.

“Even if you keep all the atoms under tight control, they can lose their ‘quantity’ [caracterstica de ser quntico] talking to your environment, warming up or interacting with things in ways you didn’t plan,” Dumitrescu explained. “In practice, experimental devices have many sources of error that can degrade coherence after just a few laser pulses.”

**temporal symmetry**

To make qubits more robust, the main approach has been to use symmetries, essentially properties that resist change. There are several types of symmetry, including rotation, inversion, rotation-inverse, translation, and time-reversal.

A snowflake, for example, has rotational symmetry because it looks the same when rotated by 60 degrees. And the technique most used today for stabilizing qubits involves giving them temporal symmetry by firing rhythmic laser pulses at them.

It works, but Dumitrescu and his colleagues wondered if they could go further. So, instead of just one time symmetry, they started to study how to add two time symmetries using ordered but not repeated laser pulses.

They looked to quasicrystals for inspiration: Unlike traditional crystals, with their well-ordered atomic networks, and glasses, with their total disorder, quasicrystals have patterns that don’t seem to fit together perfectly and never repeat themselves.

While a periodic laser pulse alternates (A, B, A, B, A, B, etc.), the researchers created a quasi-periodic pulse regime based on the Fibonacci sequence. In this sequence, each part of the sequence is the sum of the two previous parts (A, AB, ABA, ABAAB, ABAABABA, etc.).

This arrangement, like a quasicrystal, is ordered without repetition. And, similar to a quasicrystal, a 2D pattern is compressed into a single dimension. It’s this dimensional flattening that generates two time symmetries instead of just one: The system essentially gets a bonus symmetry from a non-existent extra time dimension.

The additional dimension of time emerges at the ends of the 10-qubit line.

[Imagem: Xu Zhang et al. – 10.1038/s41586-022-04853-4]

**Two times from the longest to the qubit**

To test their calculations, the team used a quantum processor with 10 qubits, ions of the chemical element ytterbium, which are individually held and controlled by electric fields, but which can be manipulated or measured using laser pulses.

They fired laser light at the qubits either periodically or using the sequence based on Fibonacci numbers. Attention turned to the qubits at either end of the 10-atom line, because it was there that the calculations indicated that the two simultaneous temporal symmetries could emerge – technically, because of this additional symmetry, these atoms coordinate in a new phase of matter. .

It worked out.

In the periodic test, the edge qubits held their data for about 1.5 seconds, an impressive amount of time in itself, as the qubits were interacting strongly with each other. With the quasi-periodic pattern, however, the qubits remained quantum for the entire duration of the experiment, about 5.5 seconds.

The gain stems from the fact that the extra time symmetry provides more protection for the qubit, Dumitrescu said.

“With this quasi-periodical sequence, there is a complicated evolution that cancels out all the errors that emerge at the edge. [da linha de qubits],” he said. “Because of this, the edge remains mechanically quantum coherent for much, much longer than you would expect.”

Although the results prove that the new phase of matter can act as a long-term storage mechanism for quantum information, researchers still need to functionally integrate the new phase of matter with the computational side of quantum computing. “We have this straightforward and amazing application, but we need to find a way to link it to the calculations. This is an open problem that we are working on,” concluded Dumitrescu.

**Bibliography:**

Article: *Dynamical topological phase realized in a trapped-ion quantum simulator*

Authors: Xu Zhang, Wenjie Jiang, Jinfeng Deng, Ke Wang, Jiachen Chen, Pengfei Zhang, Wenhui Ren, Hang Dong, Shibo Xu, Yu Gao, Feitong Jin, Xuhao Zhu, Qiujiang Guo, Hekang Li, Chao Song, Alexey V. Gorshkov, Thomas Iadecola, Fangli Liu, Zhe-Xuan Gong, Zhen Wang, Dong-Ling Deng, H. Wang

Magazine: Nature

Vol.: 607, pages 468-473

DOI: 10.1038/s41586-022-04853-4

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