The latest quantum breakthroughs explained simply

Australian physics professor talks through his team’s breakthrough quantum discoveries which could underpin a future communication network

Associate Professor Matthew Sellars, head of the Laser Physics Centre at the Australian National University (ANU), is trying to describe the importance of his department’s latest breakthrough in quantum computing.

“I just draw the analogy to the internet,” he tells me over the phone from Canberra. “The real power of computing didn't really hit us until we managed to network our computers.”

Dr Sellars and his team have recently made a significant breakthrough in the applications of transmitting quantum information over long distances however, it’s not been an easy task.

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“We began looking into this and the applications of quantum information about 20 years ago now,” he explains. “It started out with us saying 'we think we can do this' and what’s evolved from there is the realisation that the approach we're actually taking looks to be the most practical way of doing it.

“I won’t say this is the last piece of the jigsaw but we've got all the properties we need to make this work in a real communication network.”

The research the Laser Physics Centre has been carrying out has shown that an erbium-doped crystal is the most uniquely suited to provide the necessary memory at the right wavelength to enable a potentially global telecommunications network that harnesses the power of quantum mechanics.

The department published their first paper in 2005 where they demonstrated how they could use a similar crystal to store light for about a second or so, a significant advancement on previous storage times which had only been about a millisecond. From then on, there’s been a steady progression to develop and hone the techniques and improve storage times and wavelengths.

“When we published this idea, we weren't in a position to do the experiment ourselves but we were really surprised when no one tried it out. When we eventually got around to doing it [ourselves], it actually worked significantly better than we thought it would.”

We're also interested in doing this because we’re trying to implement quantum encryption,” Dr Sellars continues. “Quantum encryption is a replacement for public key encryption. We’re interested in it because it’s not only physically secure but it’s an application for quantum information that’s already out there.”

Quantum encryption has commercial uses but currently it can only work over short distances of around 100 kilometres.

“The reason for this is that quantum information is transmitted via light and unfortunately, if you put light down an optical slider, after about 100 kilometres, there's very little of that light left. It's the same problem that you face with normal optical communications but what you can do there is measure the light and then re-transmit it, in a process known as a repeater.”

The problem is you can't do that with quantum information because if you measure the light you actually collapse the quantum information. However, we discovered that if you can store the light for a long period you can, rather than measuring it, map it onto some system and then map it off again when you're ready. This allows you to achieve this repeater type operation but one that's actually compatible with quantum information.”

There’s currently a lot of effort going into trying to make quantum computers and quantum mechanics work in a number of countries around the world. There are groups in Geneva, Spain and the US, to name a few, and a number of them have started using erbium since Dr Sellars’ team published its findings.

“There's lots of efforts in China to make a long-range quantum communications network,” he continues. “The most impressive thing that they've done is launch a quantum communications satellite. They've also built a fibre optic network which is about 2000 kilometres long. Currently though, every 50 kilometres they have to put in light down the fibre to measure and reproduce it; doing exactly what I said you shouldn’t do.

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“However, the biggest issue with their communication network is that their repeater stations aren't quantum, which means if you were to break into those, you could tap into the messages. It’s not a big problem at the moment because the team working on it can keep it secure but this means that if someone that wasn’t the Chinese government wanted to use that network, then their message wouldn't be secure and could be accessed it.”

This is where ANU’s research becomes so important as applying their memory and repeater technology has already been proven to secure the network for anyone to use. By proving the basic tenants of quantum communication technology, they’ve opened the door to a number of other exciting possible applications.

With companies like Microsoft and Google working on quantum computers based on the technology of superconductors and a team at the University of Sydney using naphthalene, Dr Sellars believes their technology will allow for these different quantum computers to connect together and solve a number of the problems previous schemes have run into.

“The real difficulty is trying to take the small prototype quantum computers and scale them up into larger devices,” he explains. “Being able to take quantum information out of your computer and take it to a different location via an optical fibre makes it a whole lot easier to scale to bigger systems and allows you to make better use of the different sorts of technologies. It also opens new applications in terms of cloud quantum computing and the ability to remotely access a large quantum computer.”

So, will we be seeing quantum computers in action in the near future? Dr Sellars laughs.

“It's one of those things that's a bit of a hidden technology, like your fibre optic network around the country. Quantum fibre will allow for very secure banking transfers for example. It's one of those things that I expect the usage will just gradually flow down to less and less critical applications.”

Major companies and countries investing millions and billions of dollars into quantum computing and people are now thinking about the long-range possibilities for what this technology might be able to do, such as AI.

“It's a long way from being able to do that right now and we're still not too sure when it's really going to work but people have enough confidence to put these amounts of money in to see if they can get it going. It's certainly an exciting time and at the moment it's all very positive but that’s just as long as it works. It's exciting because we’re making steps but ultimately, we still don't quite know how it's all going to pan out.”