Quantum computing seems to get more than its fair share of attention compared to quantum communication. That’s despite the fact that quantum networking may be nearer to becoming a practical reality. In this second installment of HPCwire’s interview with Raphael Pooser, PI for DoE’s Quantum Testbed Pathfinder project and a member of Oak Ridge National Laboratory’s Quantum Information Science group, he discusses the state of quantum communication research.

Pooser notes, for example that the lack of robust quantum repeaters remains an obstacle to creating a quantum internet while the use of quantum key distribution (QKD[i]) to secure communications is already in limited use both in government and industry. He also emphasizes, at least in theory, it is possible to create an unhackable quantum communication network, just not easy to do. Pooser also offers some thoughts on the quantum hype cycle – it’s not all bad, he says, and most companies have a realistic view of quantum’s likely timetable.

HPCwire: I know there’s been a lot of work in quantum communications to make it more robust and cover longer distance. What’s happening in that area?

Raphael Pooser: That’s actually a big area of research in our quantum information science group. We have three teams – communication, sensing, and computing. We found a lot of companies want to hear about quantum communications because they’re quite concerned with cyber security. At Oak Ridge we’ve even licensed products to startup companies that are specifically based around quantum cyber security. Quantum random number generators, for example, that we’ve licensed to a start-up so that they can build quantum communication devices are based on the security of physics rather than [classical] computational complexity.

Not a lot of people know quantum communication is a big area of interest to the US electric grid. So again, back to DoE, but not the science arm of DOE, but the power and the energy science side of DOE which is required to protect the electric grid. DoE is funding a lot of research at various national labs, [such as] Los Alamos, Oak Ridge, and Brookhaven to study how to secure the grid with quantum key distribution (QKD). A lot of companies ask us about QKD. It’s one of the things, for example, Kaiser is interested in and I’ll talk about that next tomorrow as well [when I visit there].

HPCwire: What makes quantum communications secure? There seem to be conflicting claims about what quantum communications can and can’t do with regard to cyber-cryptography?

Raphael Pooser: There are limitations and maybe what you you’re picking up on are ways that people are hacking quantum key distribution. Quantum key distribution or quantum communication generally first came out a long time ago. One of the most popular schemes was invented in 1984 for example. Since then people have been trying to hack it because the original claim was it isn’t hackable. The key point is that it is unhackable by your traditional classical means. You can’t do things like intercepting, resend, man-in-the-middle eaves dropping, or cracking a code because there’s no code to crack. But people resorted to interesting new ideas for hacking, basically physics-based hacking. Now people attack the physics of these systems and are trying to discover ways to steal the secret keys by making those physics-based assumptions upon which the security is based untrue. It’s a whole different type of hacking. There have been a few successful demonstrations of bona fide hacking of quantum key distribution systems using physics based approaches.

The good news is there are unconditionally secure quantum key distribution, quantum communication schemes out there. The thing to know about why some implementations may not be absolutely secure under all conditions is because they relax some of the physics assumptions that go into them when they build them so that they can make a more practically buildable system. Some of the systems that have the true, fully unconditional security based on the physics are more difficult to build. They’ve been built though in the laboratory and demonstrated in the laboratory. So you really can build unconditionally secure systems. It’s just that they’re a bit harder.

HPCwire: Is quantum communication closer to practical reality and wide-spread use than quantum computing?

Raphael Pooser: That’s a very interesting question. In some ways, yes. In some ways, no. Here’s what I mean by that. If you have a quantum communications network that is regional, you know, it’s not very long range, then absolutely it’s useful and you can look around and see various quantum communication networks actually operating right now. [Think] secured voting results. You’ve probably heard of this example in Vienna, they secured voting results by sending the results using quantum communications down the street from the polling station to the Capitol building. And banks use it already. You can see quantum communication used in quite a few places.

Now, if you’re thinking about things like really widespread quantum communication, like a quantum internet, where you have a nationwide network of quantum communication from coast to coast, that is probably as far off as fault-tolerant quantum computing. So there’s different levels of usability. You can network quantum mechanically right now on a regional scale fairly well. But a national scale internet level networking is very far off and it’s because of the key requirement called a quantum repeater, right? That doesn’t get doesn’t exist yet.

HPCwire: I saw a recent report by researchers in China who were using atomic ensembles as a base for repeaters. They reported getting more predictable results and getting better distance, around 50 miles, and it looked promising as a potential technology for use as quantum repeaters.

Raphael Pooser: What’s interesting about this result is they’re using a quantum memory. When you talk about an ensemble of atoms, you’re thinking about using them as a quantum memory. You couple the photons, the quantum information for the photons, into the atoms and then you couple the quantum information back from the atoms when you’re ready to proceed with the repeater operations. What’s interesting is integrating that [kind of quantum memory] into a quantum communications system. The distance of 50 miles itself is not quite so impressive. It doesn’t exceed any current record for repeater-less communication. The next step would be to incorporate a repeater, the memory-based repeater, into a system that goes a longer distance than you currently could do without a repeater.

So there’s two steps here. What they’ve done is step one which is to integrate this quantum memory system into their communication system. They demonstrated the functionality, but not the distance. The next step is to show that it actually works to get you a longer distance because that’s what bridges the coasts in a quantum network; it is the quantum repeater. There’s a lot of work on repeaters right now in the U.S. as well [as China]. There’s a lot of quantum memory work going on especially within DOE [including] memory-based repeater work at Brookhaven. At Oak Ridge we are working on what we call memory-less repeaters. Those are repeaters that don’t require coupling into and out of atoms. Those are all optical devices.

HPCwire: Isn’t signal loss still a problem there?

Raphael Pooser: It’s a problem with every repeater including the memory ensembles because what’s important is how much quantum information you can get in and out. When you have lots of loss one of the things you can do is try to correct for it using quantum error correction inside the repeater. Another way is to try to distill out a very nice high-quality quantum state that can still be used as a resource for communication. Those two are definitely paths forward to trying to help correct for this information loss.

HPCwire: Will you present next week at the APS meeting? [This meeting was eventually cancelled as result of the COVID-19 pandemic]

Raphael Pooser: Not personally, but many of my team will be there. I’m actually on my way right now to a conference on the West Coast at Kaiser Permanente (health care). They want to know about quantum computing and I’m on my way to talk to them about just the general idea of quantum technology and what it could be good for us more, more outward.

HPCwire: Isn’t a bit early still for real applications. What are your thoughts on controlling the hype, which seems everywhere. It still seems like it will be a long time before Kaiser Permanente is going to be able to use quantum computing.

Raphael Pooser: Maybe. It may be a long way off and there is a question of hype. I think that we are in a state of high hype. We are in a state of high-risk and-high reward research and it’s important for people to explain to the public that this is high risk research. It’s not a 100% done deal that quantum computing, especially of the fault-tolerant type, is going to solve most problems of interest and is around the corner.

I think the reason the hype is high is because there have been some key results in recent years that encouraged everyone. Folks like Kaiser, people from health care companies to oil companies and gasoline producers, are interested in quantum computing because they’ve seen these promising early results in areas like chemistry, nuclear physics, computational fluid dynamics, and also in in AI and machine learning. What I like about this hype cycle is it’s a substantive-driven hype cycle. In other words, it’s driven by real scientific results. It’s definitely possible that things are getting overhyped right now. But at the same time, these companies don’t want to miss out on understanding what’s going on. A lot of companies that are really active asking us what’s going on with quantum technology are coming in with their heads on straight. They are asking about quantum information science more generally and they don’t say what can I do tomorrow with it? They say, what does this mean for us in the future because we don’t want to lose the competitive edge, even if it’s 10 years out?

I’ll just say something else about these companies. They’re not just interested in quantum computing. There are some nearer term technologies they’re interested in and those are the technologies of quantum sensing, and potentially quantum networking, or quantum communications. Quantum computing is a big driver of their interest, but they want to hear about these other quantum technologies that are getting a lot less hype, but are potentially very impactful as well.

HPCwire: Thanks for your time.

[i](Brief QKD Backgrounder – Quantum key distribution is currently the main way to implement quantum-secured communications. In essence, a quantum system generates a random key to encode a message. The key is used to encrypt the message and the key is shared between parties in such a way that any attempt to discover the key – in physical terms, measure it – causes detectable changes so both parties immediately know a third party has tried to read the message. The latter would trigger a resend cycle involving use of a new key. Implementation schemes vary. Quantum cryptography is only used to produce and distribute a key, not to transmit any message data. Here are links to a few explanations: Wikipedia, Wired, EC Quantum Flagship Project, and Physics.org.)