Nav: Home

Coping with errors in the quantum age

November 05, 2018

The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least at a handful of selected tasks. The numerous advances notwithstanding, today's quantum information processors still struggle to cope with errors, which inevitably occur in any calculation. This inability to efficiently rectify errors hinders in turn efforts towards sustained large-scale processing of quantum information. Hence the excitement for a set of experiments in which the group of Jonathan Home at the Institute for Quantum Electronics integrated for the first time a range of elements needed for performing quantum error correction in a single experiment. These results have been published today in the journal Nature.

Making imperfection tolerable

Just like their classical counterparts, quantum computers are built from imperfect components, and they are far more sensitive to disturbances from the outside. This leads inescapably to errors as calculations are executed. For conventional computers, there exists a well-established tool kit for detecting and correcting such errors. Quantum computers will rely even more on locating and fixing errors. This requires conceptually different approaches that take into account that information is encoded in quantum states. In particular, reading out quantum information repeatedly without disturbing it, as is needed for detecting errors, and reacting in real time to reverse these errors pose considerable challenges.

Repeat performance

The Home group encodes quantum information in the quantum states of single ions that are strung together in a trap. Typically, these strings contain ions of only one species. But PhD students Vlad Negnevitsky and Matteo Marinelli, together with postdoc Karan Mehta and further colleagues, have now created strings in which they trapped two different species, two beryllium ions (9Be+) and one calcium ion (40Ca+). Such mixed-species strings have been produced before, but the team used them now in novel ways.

They made use of the distinctly different properties that the two species possess. In particular, in their experiments beryllium and calcium ions are manipulated and measured using very different colours of light. This opens up an avenue for working on one species without disturbing the other. At the same time, the ETH researchers found ways to let the unlike ions interact with one another in manners that measurements on the calcium ion yield information about the quantum states of the beryllium ions, without corrupting those fragile states. Importantly, the physicists monitored the beryllium ions repeatedly as they were subjected to imperfections and errors. The team performed 50 measurements on the same system, whereas in previous experiments (where only calcium ions were used) such repeated readout has been limited to only a few rounds.

Corrective action

Spotting errors is one thing, taking action to rectify them another. To do the latter, the researchers developed a powerful control system for repeatedly nudging the beryllium ions depending on how much they strayed away from the target state. Bringing the ions back on track required complex information processing on the timescale of microseconds. As the system uses classical control electronics, the approach now demonstrated should be useful also for quantum-computation platforms based on information carriers other than trapped ions.

Importantly, Negnevitsky, Marinelli, Mehta and their co-workers demonstrated these techniques can also be used to stabilize states in which the two beryllium ions shared entangled quantum states, which are states that have no direct equivalent in classical physics. Entanglement is one ingredient that endows quantum computers with unique capabilities. Moreover, these states can also be used to enhance the accuracy of precision measurements. Ingredients for error correction such as the ones now demonstrated can make these states last longer -- providing intriguing prospects not only for quantum computation but also for metrology.
-end-


ETH Zurich Department of Physics

Related Quantum Computers Articles:

One step closer future to quantum computers
Physicists at Uppsala University in Sweden have identified how to distinguish between true and 'fake' Majorana states in one of the most commonly used experimental setups, by means of supercurrent measurements.
Dartmouth research advances noise cancelling for quantum computers
The characterization of complex noise in quantum computers is a critical step toward making the systems more precise.
Spreading light over quantum computers
Scientists at Linköping University have shown how a quantum computer really works and have managed to simulate quantum computer properties in a classical computer.
Newfound superconductor material could be the 'silicon of quantum computers'
Newly discovered properties in the compound uranium ditelluride show that it could prove highly resistant to one of the nemeses of quantum computer development -- the difficulty with making such a computer's memory storage switches, called qubits, function long enough to finish a computation before losing the delicate physical relationship that allows them to operate as a group.
Quantum computers to clarify the connection between the quantum and classical worlds
Los Alamos National Laboratory scientists have developed a new quantum computing algorithm that offers a clearer understanding of the quantum-to-classical transition, which could help model systems on the cusp of quantum and classical worlds, such as biological proteins, and also resolve questions about how quantum mechanics applies to large-scale objects.
More Quantum Computers News and Quantum Computers Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...