Quantum computers need tip-top error corrections

A team of quantum physicists have shown that large-scale quantum computers can be built with technology currently available, when combined with error-correction techniques.

The study, carried out by an international team of researchers and published in Physical Review X, shows that if suitable error-correction is used, ion-trap technologies are suitable for building large-scale quantum computers.

“We still fail in running complex computations because environmental noise and errors cause the system to get out of control,” said quantum physicist Rainer Blatt from the University of Innsbruck and the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences. “By using quantum error correction, we can respond to this challenge better.”

In order to do this they introduced new variants of fault-tolerant protocols and investigated how these can be implemented with currently available operations on quantum computers. The researchers found that a new generation of segmented ion traps offers ideal conditions for the process: Ions can be shuttled quickly across different segments of the trap array. Precisely timed processes allow parallel operations in different storage and processing regions. By using two different types of ions in a trap, scientists may use one type as carriers of the data qubits while the other one may be used for error measurement, noise suppression and cooling.

Classical computers use similar schemes to detect and correct errors during data storage and transfer. Before data is stored and transferred, redundancy is added, usually in the form of additional bits to allow the detection of errors. Scientists have developed comparable schemes for quantum computers, where quantum information is encoded in several entangled physical quantum bits.

“Here we exploit quantum mechanical properties for error detection and correction,” explained team member Markus Müller from Swansea University. “If we can keep the noise below a certain threshold, we will be able to build quantum computers that can perform quantum computations of arbitrary complexity by increasing the number of entangled quantum bits accordingly.”

The team say they have shown through complex numerical simulations of the new error correction protocols how the hardware of next generation ion-trap quantum computers has to be built to be able to process information fault-tolerantly.