Trinity Quantum Alliance Researcher Dr Alexander Nico-Katz: What Quantum Computers Can and Cannot Do.

The TQA is a collaboration that brings together experts in research and industry for innovative projects in quantum science and technology, simulation, education and computation. Nico-Katz talks with researchMATTERS about his work in the TQA with quantum computers: giving a breakdown on the information games that help to quantify information loss in quantum computers, overhype in the industry, and the approaching era of quantum computation.

Quantum vs Classical Computers

To begin with, then, what is quantum technology? Quantum computers can’t do anything different than regular classical computers can. Instead, they exploit fundamentally quantum phenomena to do certain things more efficiently. Nico-Katz explains: “A good example might be finding the shortest path between two locations, given a set of intermediate locations. That’s a very complicated problem that has implications for logistics, shipping, sorting. Quantum phenomena might give us a way to find certain solutions much faster than a classical algorithm would.”

This field of physics, known broadly as quantum technology, looks at distinctions between quantum and classical technology to discover what areas quantum can improve on. “Classical and quantum,” Nico-Katz notes, “are usually defined in relation to each other.” For example: if you repeat an experiment a thousand times for a classical system, you get one statistical result, and if you do the same for a quantum system, you get a different, stronger, result. “The stronger is critical here. Quantum systems can sustain more complicated correlations than classical ones can. Classical mean things are correlated in a way that is consistent with coin tosses and dice rolls. Nice simple stuff. At the fundamental level, you can’t describe quantum processes in terms of those classical ones.” Perhaps these stronger correlations can enable solutions to otherwise prohibitively difficult technical problems - like the shortest-path problem.

Can Quantum Computers do nothing?

Quantum physicists are concerned with minute changes in environment and external errors that effect the running of a quantum computer, or errors in the apparatus and set up of the machine itself. Quantum computers are much smaller than classical computers, which means they are very vulnerable to errors, such as magnetic field spikes or a sudden change in temperature above absolute zero. This is why they are kept in cold rooms.

Nico-Katz joined TQA over a year ago when it was being established due to the rising interest in quantum research in Ireland. “We wanted to actually put these quantum machines to use,” he adds “They have been built, we might as well use them, that’s kind of the fun.” He was hired by TQA Director, Professor John Goold, to work alongside his Thermodynamics and Energetics of Quantum Systems Group (QuSys).

Nico-Katz and his team are specifically interested in scenarios where the quantum computer is set up without any external sources of error, which enables them to explore information loss within the system itself. “There’s going to be movement of information natively within a system. We want to know how much information is lost to that.” This is where the title of his recent paper, “Can Quantum Computers do nothing?” comes from. If you want a computer to do something useful, you need to reliably know that it’s going to do nothing when you want it to do nothing.

Information Games

Currently, quantum computers move information around in ways that the user may not want or may not even know about. This information is still in your computer: it’s just been moved. And while this movement may not seem significant while quantum machines are small, as computers get more precise, this represents a fundamental limit. Quantum physicists use a discipline called Information Theory to address these issues. Some have reframed this idea as ‘betting games,’ using information available to increase the chance of winning a bet slightly more reliably.

Doing so, they’ve discovered that information isn’t moved to any specific location. Instead, it’s been distributed throughout the whole quantum machine, and is irretrievable unless you can see the totality of the device. “It’s sort of like taking something you wrote, reading the first half and it’s gibberish, then reading the second half and it’s gibberish. But if you read the whole thing altogether, suddenly it makes sense. In other words, we reframed quantum computers and idle information loss in terms of these betting games, and we found out how the initially organized and readable information gets non-locally distributed.”

Nico-Katz stresses that this is an abstract way of looking at theoretical and computational research. In practice, physicists work with very well-defined, often deterministic, systems, within a framework called quantum mechanics, which describes how the state of something evolves over time, or the equations of motion that govern the system. “What I do is construct quantum systems, try to come up with ones that are close to experiment or related to experiment, and then I search for what I believe to be interesting behaviour within these systems. All centred around, for me, information theory, betting games, and computation.”

The Future of Quantum

Where, then, is quantum’s brave new frontier? Nico-Katz is excited at what may become, in the next five to ten years, the fault tolerant era of quantum computation. Achieving fault tolerance means that a lot of the issues with errors in quantum computers will be fixed, meaning that quantum computers will go from something physicists are analysing as a problem in their own right to something they use to analyse other, more practical, problems.

Considering this emerging frontier of Quantum technology, it’s important to be cognisant of the potential of such technology. There’s been an over-hyping of Quantum technology, Nico-Katz notes, which is a concern for many physicists. “I describe it in terms of: you could hook up your washing machine to a V8 engine, but why? It’s using more energy and it will probably break your machine.” He attributes the growth of the quantum hype industry, and the proliferation of outlandish claims to “capitalist hyperaccelerationism” or a “bulbous outgrowth of ideas which multiplies out in all directions, which is good, but it means a lot of wildly over-zealous claims are made and then picked up as fact.” This hype also delegitimises very interesting fields of study that may not appear as immediately profitable.

Where quantum technology will shine is in the context of problems with few inputs and complicated dynamics. He gives the example of materials optimisation. “I’ve got this hypothetical molecule and I want to know its structure, its effect. That can lead to discovery of materials with incredibly high refractive indices, or to new medicines, or higher efficiency fibre optic cables, incredibly powerful solar cells, and novel insulators. I have no doubt quantum physics is going to affect those sectors, health, energy, and materials science, significantly.”

Personally, he is looking forward to quantum technology which realizes genuine many-body systems. “The way we understand technology is usually that we build a component, and we stack all those components next to each other and scale it up, to build more complicated assemblages of those components.”

But, highlighting ‘More Is Different,’ a favoured essay of Nico-Katz’s by Nobel Laureate Philip Anderson, “when you make a quantum system big enough with enough component parts, it becomes a new type of system.” Nico-Katz points out that “We are now at the point where we can build one atom at a time: you can just build any material you want, and it in itself is a new material. And that’s a hell of a frontier to get excited about!”

- Profile by Dr Sarah Cullen