Errors expected to affect quantum computing have been partly addressed by a team of scientists, which is a step forward towards the realisation of a practical quantum computer.
Quantum computers promise to open up new capabilities simply not possible using today’s computers, yet progress toward commercially useful machines has been slow.
But researchers from IBM’s Watson Research Centre have successfully demonstrated two critical methods for correcting quantum errors on a circuit.
The IBM findings were published in the journal Nature Communications, which showed for the first time the ability to detect and measure the bit-flip and phase-flip errors simultaneously that will occur in any real quantum computer.
“Up until now, researchers have been able to detect bit-flip or phase-flip quantum errors, but never the two together,” said Jay Gambetta, a manager in the IBM Quantum Computing Group.
The team demonstrated its error-protection protocols on a quantum bit circuit based on a square lattice of four superconducting qubits on a chip roughly one-quarter-inch square.
By going for a square-shaped design rather than a linear array, IBM claims it made it more scalable than the ones that have been used by other groups.
“Previous work in this area, using linear arrangements, only looked at bit-flip errors offering incomplete information on the quantum state of a system and making them inadequate for a quantum computer, said Gambetta.
“Our four qubit results take us past this hurdle by detecting both types of quantum errors and can be scalable to larger systems, as the qubits are arranged in a square lattice as opposed to a linear array.”
Although significant, Professor Alan Woodward, a computing expert from the University of Surrey, UK, told the BBC the work was a “significant evolution” rather than a “revolution”.
“We all know that error correction is very important in quantum computing because of the inherent errors that are caused by the way qubits tend to operate, but this isn't the first time it's been addressed,” he said.
He also said the dark horse in the race was topological quantum computing, an architecture that is more fault-tolerant.
Detecting quantum errors
Traditionally, in a typical computer, the basic units of information are bits. Similarly to how a beam of light can be switched on and off, a bit can have only one of two values, 1 and 0. However, a quantum bit can be both 1 and 0 at the same time.
In theory, this superposition property is what gives quantum computing much greater power over the conventional type, allowing quantum computers to choose the correct solution among millions of possibilities much faster.
But it also means that the two errors, bit-flip and phase-flip, can occur and must be detected in order for quantum correction to function properly.
The scientists used different techniques to measure the states of two independent syndrome qubits. Each revealed one aspect of the quantum information stored on two other qubits (called code, or data qubits).
Specifically, one syndrome qubit revealed whether a bit-flip error occurred to either of the code qubits, while the other syndrome qubit revealed whether a phase-flip error occurred.
Determining the joint quantum information in the code qubits is essential for quantum error correction because directly measuring the code qubits destroys the information contained within them.
Because these qubits can be designed and manufactured using standard silicon fabrication techniques, IBM anticipates that once a handful of superconducting qubits can be manufactured reliably and repeatedly, and controlled with low error rates, there will be no fundamental obstacle to demonstrating error correction in larger lattices of qubits.
With Moore’s Law expected to run out of steam, quantum computing will be among the inventions that could usher in a new era of innovation. Quantum computing could allow scientists to design new materials and drug compounds reducing the cost and trial and error experiments in the lab, potentially speeding up the rate and pace of innovation.
For a world consumed by Big Data, quantum computers could also quickly sort and curate ever larger databases as well as massive stores of diverse, unstructured data. This could transform how people make decisions and how researchers across industries make.