In what’s being referred to as a major breakthrough for quantum computers, researchers at John Martini’s University of California (Santa Barbara) lab have developed quantum circuitry that is able to self-check for errors and suppress them.
This capability preserves the qubits’ state(s), thereby providing the system with an unprecedented level of reliability, which will prove foundational for the building of large-scale superconducting quantum computers.
“One of the biggest challenges in quantum computing is that qubits are inherently faulty,” said Julian Kelly, graduate student researcher and co-lead author of a research paper that was published in the journal Nature. “So if you store some information in them, they'll forget it.”
Unlike computing as we know it today, where data bits exist on one or two binary positions, qubits can exist at any and all positions simultaneously, and in various dimensions. This property, referred to as “superpositioning”, gives quantum computers their amazing and seemingly limitless computational power; it also, unfortunately, makes the qubits prone to “flipping”, especially in unstable environments.
“It’s hard to process information if it disappears,” Kelly added.
The process the team at Martini’s lab created involves a scheme in which several qubits work together to preserve information; that is, information gets stored across several qubits.
“And the idea is that we build this system of nine qubits, which can then look for errors,” Kelly explained.
Specifically, qubits in the grid are responsible for preserving the information contained in their neighbors in a repetitive error detection and correction system that can protect the appropriate data and store it longer than any individual qubit can.
“This is the first time a quantum device has been built that is capable of correcting its own errors,” staff scientist Austin Fowler remarked.
It’s an important milestone for computer science, too, because the type of complex calculations researchers envision quantum computers performing, nearly a hundred million qubits would be needed. As such, a self-check and error prevention system is necessary to ensure absolute accuracy.
Taking a closer look at the team’s solution, the key to the error detection and correction system is a scheme developed by Fowler called the “surface code”. It uses parity information, which is different from the information duplication error detection process used in today’s computing systems. This decision was made so that the original information being preserved in the qubits remains un-observed and thus, undisturbed.
“You can't measure a quantum state, and expect it to still be quantum,” explained postdoctoral researcher Rami Barends. What he is referring to is the fact that actually measuring the state locks the qubit into a single state; this reaction, if you will, causes it to lose its superpositioning power.
Parity information, on the other hand, does not disturb the qubit, and is actually quite similar to a Sudoku puzzle: the parity values of data qubits in a qubit array are taken by adjacent measuring qubits, which asses the information in the data qubits by measuring around them.
“So you pull out just enough information to detect errors, but not enough to peek under the hood and destroy the quantum-ness,” Kelly sums up.
This solution that the team at Martini’s lab has provided the technology industry provides a meeting point for the best in the science behind the physical and theoretical in quantum computing — it’s the latest innovation in qubit stabilization, and also significantly advances the algorithms behind the logic of quantum computing.
“It's a major milestone,” said Barends. “Because it means that the ideas people have had for decades are actually doable in a real system.”
So far, the group’s quantum error correction scheme has proven to protect against the “bit-flip” error; next up, the researchers want to focus on correcting the complimentary error called “phase-flip”. They also want to run error correction cycles for longer periods to diagnose and analyze any particular behaviors.
Since their research was demonstrated, Martinis and the senior members of his research group have entered in to a partnership with Google.
You can read the full study in Nature. It was published under the title, “State preservation by repetitive error detection in a superconducting quantum circuit”.
Via: Phys.org
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