Time will tell if quantum computers can overcome this problem

31 Oct 2023

Image: © Ulia Koltyrina/Stock.adobe.com

A study led by Trinity’s Dr Mark Mitchison has found that accurate timing is even more crucial to realising quantum computers than previously thought.

Despite all the progress we’ve made in understanding the world around us since the age of scientific inquiry first began, there is likely more about the universe that we don’t understand than we do. And while this is certainly true in the case of stars and galaxies, the macro world as it were, it is even more obvious when we delve into the world of quantum physics.

In the latest discovery around the elusive world of quantum, an international consortium of researchers led by Trinity College Dublin (TCD) academic Dr Mark Mitchison has found that imperfect timekeeping places a fundamental limit on quantum computers and their applications.

This means that timing is even more crucial to quantum computing than previously thought, and that even the most minute of timing errors can add up to significantly impact any large-scale algorithm running on a quantum computer.

“A quantum algorithm is like an app that runs on a quantum computer,” explained Mitchison, whose team published a paper on their findings in the Physical Review Letters this month.

“It was already known that timing errors could disrupt individual quantum logic gates, which are the building blocks of quantum algorithms. Our work extends this to full quantum algorithms, showing exactly how precise the clock must be to achieve a given computational accuracy.”

Modern clocks, especially digital ones, are very accurate for all practical purposes. But this latest study shows that accuracy is even more essential for quantum computers because of the nature of particles they work with to process information, such as atoms, electrons and photons.

Then there is the fact that current quantum computers are too small to be useful, with a major challenge being the fragility of the quantum states that are used to encode information.

“Mathematically speaking, changing a quantum state in a quantum computer corresponds to a rotation in an abstract high-dimensional space,” explained Jake Xuereb of the Atomic Institute at Vienna University of Technology, first author of the paper.

“In order to achieve the desired state in the end, the rotation must be applied for a very specific period of time – otherwise you turn the state either too little or too far.”

And because this error gets worse for more complex algorithms, it will ultimately pose a significant challenge in the realisation of working quantum computers. But according to Prof Marcus Huber, who leads the research team in Vienna, this is not a problem at the moment.

“Currently, the accuracy of quantum computers is still limited by other factors, for example the precision of the hardware components or the effect of stray electromagnetic fields,” he said.

“But our calculations also show that, today, we are not far from the regime in which the fundamental limits of time measurement will play the decisive role.”

10 things you need to know direct to your inbox every weekday. Sign up for the Daily Brief, Silicon Republic’s digest of essential sci-tech news.

Vish Gain is a journalist with Silicon Republic