Quantum computing's immense promise in fields such as chemistry and cryptography is also its greatest challenge: any hint of error or tampering brings the whole computation crashing down. The only way around this is to use multiple quantum bits (qubits), the building blocks of quantum information, to essentially back each qubit up. But in practice this becomes impossible if the quantum computer gets too large.
"In current quantum processors, you always have some errors, and so you might think, OK I'll just add a few more qubits for protection," said physicist Alexey Gorshkov of the Joint Quantum Institute at the University of Maryland. The problem is that you start to need exponentially many more qubits to correct exponentially decreasing levels of error. "Eventually it's just unrealistic."
In their paper, published in Nature Physics, Gorshkov and his co-authors found that using special, "topologically ordered," arrangements of qubits could eliminate the need for exponential resources to correct errors. "Our insight was, wait a minute, is it possible to do some sort of topological quantum error correction (TEC)," which could lead to the "holy grail" of polynomial overhead? said Gorshkov, who is also with the National Institute of Standards and Technology. "That's the major finding of our paper."
Their idea boils down to "error-correcting codes which are built from topological states of matter—states of matter that have no local order, but instead are characterized by long-range correlations that can be used to detect and correct errors," according to a Nature Physics News & Views article.
The breakthrough will also have implications beyond quantum computing, says Gorshkov, in fields such as high-energy particle physics and statistical physics. "Quantum error correction is a universal technique for controlling errors in all quantum systems, not just in a quantum computer," he said. "There are many other physical systems where these techniques can be tried out, and that's really exciting."
