Oak Ridge National Laboratory recently became one of a handful of organizations funded by the Department of Energy to develop the underlying technology required to build a Quantum Internet. The move came at roughly the same time ORNL reorganized its quantum research under a Quantum Information Science Section (QISS) headed by Nicholas Peters.

As described by Peters, “That’s sort of the biggest organization size you can have without being led by a professional manager. So I’m a scientist. My day job is running science projects. I came to Oak Ridge in 2015 and the quantum networking we had at the time was mostly focused on quantum key distribution. That work was funded by the Department of Energy’s Cybersecurity, Energy Security, and Emergency Response (CESER) office [which had] a Cybersecurity for Energy Delivery Systems (CEDS) program. That was what our quantum networking research was until a couple of years ago, when the Department of Energy’s Office of Science started funding Quantum.”

“The way DOE does stuff is they have workshops, you write a workshop report, and they decide if they want to make a program in it. Typically, they ask for proposals and point to a workshop report. So we did that. We started quantum networking a couple years ago and had this quantum internet workshop [to discuss] the quantum networking research that needs to still be done. So we’re a long way from having a quantum internet,” said Peters. The proposal was accepted and funding arrived last October.

It’s not hard to see why the DOE would want a working quantum internet, “It’s not a secret that DOE is investing heavily in quantum objects, developing quantum computers and things like that. If we have real quantum computers sitting at the National Labs, there’s going to be value in connecting those resources with the quantum network. We’re still a long, long, way from doing that. Right now we have the Energy Sciences Network (ESnet), which connects with a high-performance network, the national labs. If we have quantum resources sitting at the National Labs, the idea is that we’d like to have a quantum network that connects them. For example, you could take my take my special resource (photon) states at Oak Ridge and send them through the network to another national lab,” said Peters.

Presented below are a few of Peters’ comments to HPCwire during a discussion of ORNL’s quantum internet work. Much of the work is around perfecting photon sources – including perhaps “the highest bandwidth and entangled photon source ever made” – developing error correction techniques, and exploring various quantum repeater and memory technologies. The QISS section has other non-networking quantum research areas as well.

HPCwire: Maybe get us started by comparing the state of quantum computing research to quantum networking and a quantum internet.

Peters: In the U.S. in general, the government started investing in quantum computing in mid 90s. Right. And that enables us to sit here at 2022, and have a Fortune 500 company do quantum computing, right, to buy this stuff. You know Google’s got a system. Google went and bought their research group to start to start their quantum computing effort. We’re not nearly as mature in quantum internet type research right now. So you basically have to hand build everything [such as] these entangled photon sources. You can go out and buy single photon detectors as a commercial product. But you know, for a long time, you’d spend a lot of time messing with your detector to get it to work well. But now you just go get turnkey solutions.

Eventually, photon sources will do that as well. There are some companies out there selling turnkey entangled photon sources. But what we want in our photon sources is to have extraordinarily high throughput, so really bright photon sources that are really high quality. We like to have this metric called fidelity, which is this measure of state arrival. We want to try to have 99 percent fidelity, which is almost perfect in terms of the entangled state quality. We also want to have them be entangled in only one degree of freedom, because if they’re entangled in multiple degrees of freedom, then you don’t get as good a HMO (Hong–Ou–Mandel) interference. It turns out, it’s really hard to make a high quality entangled source that’s also spectrally un-entangled.

HPCwire: What’s your take on the global competition to achieve practical quantum computing and communications?

Peters: I think in general, it’s an important thing. Think about quantum [technology] in general; there are many, many countries that just can’t afford to fund a really broad portfolio of science projects. So many of them have decided, “Well, we’re going to invest in quantum because we think it’s a big deal.” We see this across the world; different countries are really focusing their science projects and programs in the quantum space. I think a lot of people think that quantum is going to be a key technology of the future. It’s going to be the kind of thing that 100 years from now is going to be all transparently underneath the way that we just live our lives and stuff will be operating and making our lives better.

HPCwire: Let’s jump into a quick overview of ORNL’s quantum networking research?

Peters: We have four projects (brief description at end of article) in quantum networking. One of those projects is an Early Career Award for one of our junior staff named Joe Lukens. We have three projects that are bigger projects, one of which is this quantum internet project. If you know much about optical networks, there’s a hierarchy and the very lowest layer is the physical layer – that’s where we’re transmitting photons on optical fibers. The quantum internet is going to look a lot like the classical internet in that you’re going to need all of the classical stuff you have out there today, but it might not be optimized the same way that it’s optimized today. What we focus on is the physical layer.

Most of us are physicists that are working in this field, but we’ve got some computer scientists and electrical engineers working on it as well. Right now, just being able to create photons and measure them and transport them over fiber and manage that bandwidth of the entanglement is where much of our focus is. On the on the quantum internet project, our major partner is Los Alamos National Lab. They’re developing tunable sources of single photons using these carbon nanotube type technologies they’ve got. They can actually tune the wavelength of emission of these photons, which is important because typically what you’re trying to do with photons is to interfere them with each other. The type of interference you want is called Hong–Ou–Mandel interference, a really famous type of interference discovered decades ago.

HPCwire: I’ve heard of Hong–Ou–Mandel interference but don’t know much about. How is it useful in quantum communications?

Peters: [Using] Hong–Ou–Mandel interference allows you to do what is effectively a two-qubit quantum gate in linear optics. Photons naturally don’t interfere well with each other, which is good because you can send it down fiber, frequency multiplexed, and they don’t screw each other up. We have shown that you can do a complete gate-set of linear optical gates using the frequency degree of freedom [technology] that was invented at ORNL. Part of what we’re going to be doing is use that same frequency technology to do a management of the quantum signals and teleportation [i.e. quantum information sharing].

This linear optical teleportation and a two-qubit gate both use that same Hong–Ou–Mandell interference. We’re developing those [interfered photon] sources at Los Alamos. We’re also developing a special two-photon source at ORNL, which is based upon an earlier [work] that ORNL published over a decade ago, but we want to make the quality a lot better so we can use it for teleportation experiments between us and the University of Tennessee, Knoxville, who’s another one of our university partners. Those are the two major [photon] sources that we’re working on in this quantum internet project.

HPCwire: Error correction is a major hurdle generally in quantum computing. How much of a problem is it and how is error correction being tackled in quantum networking?

Peters: We’re looking at error mitigation. This is another thing that touches closely to the regular internet. We’re sending photons down actual fibers that are deployed between telephone poles in a lot of cases and the wind blows and makes your polarization get scrambled. You have to correct for that. So there’s all of these out-of-band, analog channels you have to keep track of in order to keep them from messing up your states. In the quantum world, we’ve got these qubits, right, so everything’s an analog system; that’s unlike the digital internet where everything is a bit. Also, in the quantum case, you’re transmitting a photon down a fiber and most of the time it doesn’t get [to the end]. Most of the time, it’s lost because fiber has exponential loss. To get around that exponential fiber loss we have to build a quantum repeater, and a quantum repeater basically uses these collections of gates – these two-qubit gates –  and basically you could think of it as kind of a quantum error correction for photons.

There are a couple of different quantum repeater approaches out there. The oldest ideas are ones where we distribute entanglement and hold one of those entangled photons at a quantum memory. That quantum memory would be really useful thing, if you had it. Turns out there are other approaches that don’t require quantum memory to do quantum communications and quantum repeaters; these are all optical ways. We’re working on one of those – all optical quantum repeaters – in collaboration with the guys at University of Arizona.

HPCwire: Are you also working on quantum memory approaches?

Peters: Yes. We’re also collaborating with Purdue in the quantum internet project to build a quantum memory out of Thulium. We’re picking that particular atom because people have demonstrated that it works pretty well at shorter wavelengths to store photons. It’s got a long coherence time. We’re trying to push that out to the operation of the telecom band – so long, long wavelengths, longer than we think we will actually operate at but that still will go down an optical fiber. That’s one of the most exciting parts of that project, trying to get this quantum memory to work. Purdue will hopefully be getting that to work and to send it to us and we’ll install it on our optical fiber testbed.

HPCwire: How much influence will existing communications technology have? Can you reuse it?

Peters: I’m not aware of any quantum communications protocol that doesn’t also require classical communications. You’ll need the classical network to support the quantum part of the network. On current networks, a variety of technologies compete and coexist in modern optical networks. It’s going to be no different when you add quantum. Back in 2006 to 2009 we did some of these experiments to try to integrate quantum key distribution into the optical networks. It turns out, it’s really hard to do that. But you know we’re sort of trying to do that because we wanted to make sure we can get it to work on an optical network and not and require a dark fiber to do it.

One of the things that we’re looking at, in the context of building these quantum repeater networks, is trying to understand what noise sources you get from classical signals and how they would impact the kind of quantum error correction codes that you would need to build to try to fix the quantum information. Where we’re going with that is, we are developing a different kind of quantum light source called a squeezer. That will allow us to generate these squeezed states of light that are useful for building quantum sensors. They’re also potentially useful for building a quantum repeater. We’re working with Arizona and one of its professors who’s developing these integrated optical squeezers. [At ORNL] we’re developing optical squeezers that aren’t integrated – they’re bulk just so we can have a squeezed-state resource to do some of this repeater research.

HPCwire: How does using squeezed light help? Is this similar to the technology Xanadu uses for its photon-based quantum computer?

Peters: Actually, Xanadu founder (and CEO) Christian Weedbrook was a postdoc who worked with me on a multi-institution project. Where we are going eventually – we just did a paper on it – is the idea that we can take a bunch of these integrated squeezers, do some frequency domain processing, like quantum processing based upon the gate-set that I mentioned earlier that we invented at ORNL. Then we can do conditional detection on the output modes of some of those frequency-squeezed states and ideally herald one of these states that are useful for protecting quantum information, so one of these error correcting codes.

The theory of that right now is that we know how to create a special kind of state called a ‘cat state’. We still have to do a lot more work though to get one of these error correction codes. They’re called the GKP qubits. That stands for Gottesman-Kitaev-Preskill and it’s a kind of continuous variable way [in which] basically, a loss error turns into a qubit error. No one has made those states anywhere in the world. We’re trying to figure out, using our unique technology, if can we can we make those. It’s still an open question if we can even make those. So that’s one of the that’s one of the other exciting things that we’re working on.

HPCwire: It’s early days for ORNL in terms of quantum networking and a quantum internet. What are some of the milestones we should look for?

Peters: Well, one of the things that I’m really excited about is a paper we’re writing up now. What we’ve done is we’ve applied Bayesian mean estimation to these continuous variable optical states, and we’ve got tomography on these different states. The idea is we have much better understanding, much smaller error bars with this new idea that we implement it. And we’re writing that up for submission to a journal, hopefully within a week or so. I’m really excited about is doing the Bayesian tomography of continuous variable states. That’s something that we hope will help with building these types of all optical quantum repeaters using that that technique.

Another thing we’re trying to build is probably going to be the highest bandwidth and entangled photon source that anyone’s ever made. And we’re going to be able to use these Bayesian techniques. We have been previously using them on characterization of polarization encoded entanglement. We’ll continue to apply those, but will have a really wide-bandwidth entangled photon source and we hope to show that it would be by far and away, by an order of magnitude, more bandwidth than we’re currently using on our optical network. We currently have eight channels of entanglement on our optical network. Hopefully, we should have at least a factor of 10 more optical channels coming out of this new source. We’ve been working on the design for that source. And hopefully, we’ll be at a point where we can demonstrate it later on in the year. Currently the parts are on order.

HPCwire: Nick, thanks very much for your time.

Link to background paper (Reconfigurable Quantum Local Area Network Over Deployed Fiber): https://journals.aps.org/prxquantum/pdf/10.1103/PRXQuantum.2.040304

Link to report on ORNL quantum science expansion: https://www.hpcwire.com/off-the-wire/ornl-reviews-quantum-research-milestones-will-triple-its-quantum-dedicated-lab-space/

Brief Peters Bio: 

Nicholas A. Peters received the B.A. degree summa cum laude in physics and mathematics from Hillsdale College, in 2000 and the M.S. and Ph.D. degrees in physics from The University of Illinois Urbana-Champaign, in 2002 and 2006, respectively.

In 2006, he joined Telcordia Technologies (formerly Bell Communications Research – Bellcore) as a Senior Research Scientist, which later became Applied Communication Sciences (ACS).  In 2012, he was promoted to Senior Scientist at ACS.  In 2015, he joined Oak Ridge National Laboratory (ORNL) as Senior Research and Development Staff Member and strategic hire.  From 2016-2021, he was appointed Joint Faculty Assistant Professor to The Bredesen Center for Interdisciplinary Research and Graduate Education at the University of Tennessee Knoxville.  In 2017, he was appointed to lead ORNL’s quantum communications team.  In 2019, he became the Group Leader for ORNL’s Quantum Information Science Group.  In 2021, he was promoted to Distinguished Research and Development Staff and later that year, inaugural Section Head of the Quantum Information Science Section.  He has been a visiting researcher at Los Alamos National Laboratory, National Institute of Standards and Technology-Boulder, The Ohio State University, and Princeton University.

He is a Member of The American Physical Society (APS) and a Senior Member of The Optical Society (OSA) and the Institute of Electrical and Electronics Engineers (IEEE).  He is an active referee, primarily for APS journals, and has served as an Associate Editor for Optics Express since June 2016.

Brief Description of Scope of ORNL’s DOE Internet Project

“…The ORNL team, which includes principal investigator and Quantum Information Science Group Leader Nicholas Peters and Wigner Fellow Joseph Lukens, will work with LANL, quantum technology company Qubitekk, Amazon Web Services, Purdue University and the University of Tennessee, Knoxville to design and deploy a quantum internet testbed capable of sending and receiving information on an intracity scale.

“UTK researchers led by physics professor George Siopsis will leverage state-of-the-art superconducting single-photon nanowire detectors to house one of the nodes in this network at the university, which is a 20-mile drive from ORNL. This node will eventually be connected to nearby nodes via future optical fiber and to more distant nodes through satellite communication systems. The QuAInT project will also provide partial financial support to train three graduate students in quantum networking.

“Over the next five years, the QuAInT team will develop numerous building blocks needed to enable the testbed and, eventually, a widespread quantum internet that could provide unparalleled storage capacity and cybersecurity advantages. Key components include quantum memory capabilities being developed at Purdue and multiple types of photon sources soon to be under construction at LANL and ORNL. These resources will eventually enable the partner institutions to share quantum data using satellites in a future space program.

“At ORNL, researchers will integrate these technologies into interconnected quantum networks and embed automated tuning features to account for changing environmental conditions. They will also combine quantum teleportation — a method of transferring qubits between disparate locations — and a previously developed resource called a frequency processor — which can arbitrarily transform the frequency properties of light — to take full advantage of the bandwidth available in quantum networks.”