Quantum error correction (QEC) is a technique used in quantum computing to safeguard quantum information from errors caused by decoherence and other quantum noise. Quantum error correction is required to enable fault-tolerant quantum computation that can deal with not just noise on stored quantum information, but also faulty quantum gates, faulty quantum preparation, and faulty measurements.
Mistakes happen, especially with quantum computers. The tiny quantum bits, or qubits, that comprise the machines are notoriously error-prone, but scientists have demonstrated that they can be repaired. Computers that use quantum mechanics rules show potential for performing calculations that are now beyond the capabilities of ordinary computers. But without a mechanism for fixing the computers’ mistakes, the answers that a quantum computer spits out could be gobbledygook.
Researchers claim in Nature that combining the power of numerous qubits into one can address the error problem. Scientists combined nine qubits to create a single, enhanced qubit known as a logical qubit, which, unlike the individual qubits from which it was created, can be probed for errors.
“This is a significant step toward building a large-scale quantum computer,” says quantum physicist Winfried Hensinger of the University of Sussex in Brighton, England, who was not involved in the current study.
Information is redundantly stored in a logical qubit. This enables researchers to check for and correct errors in the data. If a component of it goes missing, you can reconstruct it from the other pieces, like Voldemort.
David Schuster
Still, Hensinger warns, the road ahead is lengthy. To perform sophisticated calculations, scientists will need to significantly increase the amount of qubits in the devices. “There’s nothing essentially keeping us from building an usable quantum computer,” he argues, now that scientists have demonstrated that they can keep faults under control.
Information is redundantly stored in a logical qubit. This enables researchers to check for and correct errors in the data. “If a component of it goes missing, you can reconstruct it from the other pieces, like Voldemort,” says University of Chicago quantum physicist David Schuster, who was not involved in the new research.
In the latest work, four auxiliary qubits interacted with the logical qubit to detect faults in its data. Future quantum computers could do calculations utilizing logical qubits instead of the original, defective qubits, verifying and correcting any faults that arise.
The researchers created their logical qubit using a technique known as a Bacon-Shor code, which they used to qubits made of ytterbium ions floating above an ion-trapping device inside a vacuum and operated with lasers. The researchers also devised operation sequences to prevent faults from multiplying uncontrolled, a concept known as “fault tolerance.”
Thanks to those efforts, the new logical qubit had a lower error rate than that of the most flawed components that made it up, says quantum physicist Christopher Monroe of the University of Maryland in College Park and Duke University.
However, the crew did not complete the entire process for error correction. While the computer noticed the inaccuracies, the researchers did not repair the errors and continued with the computation. Instead, they corrected faults after the computer had completed its task. In a full-fledged example, scientists would detect and rectify faults on the fly many times.
Quantum error correction must be demonstrated in order to develop viable quantum computers. “It’s similar to reaching criticality with [nuclear] fission,” Schuster explains. Once the nuclear science barrier was breached in 1942, it paved the way for technologies such as nuclear power and atomic bombs.
As quantum computers gradually draw closer to practical usefulness, companies are investing in the devices. Technology companies such as IBM, Google and Intel host major quantum computing endeavors. A quantum computing company cofounded by Monroe, called IonQ, went public; Monroe spoke to Science News while on a road trip to ring the opening bell at the New York Stock Exchange.
According to coauthor Kenneth Brown, a quantum engineer at Duke University, the latest result shows that full-fledged quantum error correction is almost here. “It really demonstrates that we can put all the parts together and complete all of the tasks.”
Quantum computers are gaining popularity due to the enormous power they will possess – all while utilizing the unique capabilities of quantum physics. They will be able to outperform today’s computers, solving tasks at a rate infinitely quicker than the world’s most powerful supercomputers.
