Scientists develop new way to process quantum information

19 Sep 2023

Image: © Negro Elkha/

Claiming to have improved over previous methods, scientists based at the University of Waterloo have developed a flexible ion qubit control system.

Scientists based in Canada have made significant progress in quantum computing by developing a new method that can reliably process quantum information.

Using laser light, researchers based at the University of Waterloo Institute for Quantum Computing (IQC) have developed the most robust method currently known to control individual qubits made of the chemical element barium.

The ability to reliably control a qubit is an important achievement for realising functional quantum computers in the future.

While classic computers (the ones we use today) use bits to store and manipulate information, quantum computers rely on quantum bits or qubits.

However, as Joe Carroll of University College Cork explained recently, the problem with existing quantum computers is that each qubit “must be in a superposition” with two different energies – just as Schrödinger’s cat could be called both dead and alive.

The new method developed in Canada uses a small glass waveguide to separate laser beams and focus them four microns apart – which is about four-hundredths the width of a single human hair.

The team said the precision and extent to which each focused laser beam on its target qubit can be controlled in parallel is an improvement over previous research.

“Our design limits the amount of crosstalk – the amount of light falling on neighbouring ions – to the very small relative intensity of 0.01pc, which is among the best in the quantum community,” explained Dr K Rajibul Islam, a professor at IQC and Waterloo’s Department of Physics and Astronomy.

“Unlike previous methods to create agile controls over individual ions, the fibre-based modulators do not affect each other.”

Essentially, this means that the scientists can communicate with any ion without affecting its neighbours, while also retaining the ability to “control each individual ion” to the maximum possible extent.

“This is the most flexible ion qubit control system with this high precision that we know of anywhere, in both academia and industry,” Islam added.

Barium ions are becoming increasingly popular in the field of trapped ion quantum computation, the researchers said, because they have convenient energy states that can be used as the zero and one levels of a qubit and be manipulated with visible green light.

This contrasts with the higher energy ultraviolet light needed for other atom types for the same manipulation. It allows the researchers to use commercially available optical technologies that are not available for ultraviolet wavelengths.

Islam and his team published a paper earlier this summer in the IOP Science journal. Others on the team include Ali Binai-Motlagh, Dr Matt Day, Nikolay Videnov, Noah Greenberg and Dr Crystal Senko.

“This work is part of our effort at the University of Waterloo to build barium ion quantum processors using atomic systems,” said Senko, a faculty member at IQC and Waterloo’s Department of Physics and Astronomy.

“We use ions because they are identical, nature-made qubits, so we don’t need to fabricate them. Our task is to find ways to control them.”

Advances in quantum computing are leading to huge breakthroughs in chemistry and many other fields.

Last month, researchers at the University of Chicago claimed to have observed the phenomenon known as “quantum superchemistry”, whereby particles in the same quantum state exhibit accelerated chemical reactions.

In April, researchers in Sweden successfully used a quantum computer to solve simple chemistry problems, as a proof-of-concept for more advanced calculations.

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Vish Gain is a journalist with Silicon Republic