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QUANTUM COMPUTERS Researchers correct qubit loss in quantum computers

Author / Editor: Luke James / Johanna Erbacher

In recent research, scientists have found a way to correct qubit loss in a trapped-ion quantum processor, providing what they call a “complete toolbox” for the correction of qubit loss that constitute the building blocks of complete and scalable quantum error correction.

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An international research group has developed a new protocol that can protect and correct the fragile quantum information in instances of errors due to qubit loss.
An international research group has developed a new protocol that can protect and correct the fragile quantum information in instances of errors due to qubit loss.
(Source: IBM)

Quantum computers are amazing pieces of technology with extraordinary computing ability, far exceeding that of ‘classic’ computers, because their circuits are based on qubits that can represent not only binary (0s and 1s) but also superpositions of 0 and 1 states by using quantum mechanics.

Despite their huge potential, however, they’re not immune to mistakes; qubits are very fragile and are prone to errors due to their interactions with the external environment. This fragility is fairly problematic, holding back progress in a technology that could be truly revolutionary.

To solve this problem, an international research group has developed a new protocol that can protect and correct the fragile quantum information in instances of errors due to qubit loss. Their paper, ‘Experimental deterministic correction of qubit loss’, was published in the journal Nature in early September.

A ‘qsphere’ comparing classical and quantum states.
A ‘qsphere’ comparing classical and quantum states.
(Source: IBM Research via YouTube)

Detecting and correcting errors

While we already know that quantum processors do have a certain tolerance against computational errors, we don’t know much about how to prevent and correct the errors that are caused by a complete or partial loss of qubits.

“Developing a fully functioning quantum processor still represents a great challenge for scientists across the world,” says Davide Vodola, one of the study’s authors and a researcher at the University of Bologna. He added, “This research allowed us, for the first time, to implement a protocol that can detect and, at the same time, correct errors due to qubit loss. This ability could prove to be essential for the future development of large-scale quantum computers.”

When quantum computers elaborate data, some qubits can be totally lost from the quantum registers or they can transition to unwanted electron states. Both of these processes result in a loss that could make the quantum processor completely useless, and that’s why coming up with theory-based experimental techniques that can analyze and mitigate the impact that these errors have is of great importance.

Developing an effective theoretical approach

To solve this issue, the research group first developed an “effective theoretical approach”, says Vodola. “We managed to show that the information stored in a register with some qubits can be protected and fully retrieved in case one of these qubits gets lost.”

Afterward, the researchers developed a solution that used an additional qubit that functions as a probe which can be used to assess the presence or absence of other qubits without altering the computing process. This worked, enabling the researchers to test their protocol in real-time and see some promising results. “We are happy with the results of this test on the trapped-ion quantum processor of the University of Innsbruck,” Vodola added.

According to Thomas Monz, who led the University of Innsbruck team, all the building blocks that have been developed in this study are “readily applicable” to other quantum computer architectures and other quantum error correction protocols.

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