Is quantum computing the next big thing or forever in the future? The answer lies in whether there’s a practical way to make the crucial components for quantum computers. Now they require expensive, bulky and energy-intensive super-cooling, like to nearly absolute zero. Now a Defense Advanced Research Projects Agency (DARPA) program seeks a breakthrough in quantum computing science so it can work at warmer temperatures. For the particulars, Federal Drive with Tom Temin spoke with DARPA Program Manager Dr. Mukund Vengalatorre.
Tom Temin And Manufacturability, that’s the essential issue, right, for building quantum computers, because what they do is fairly well understood. Would that be a fair way to characterize the situation?
Mukund Vengalatorre That would be a fair way. So I would use the word scalability rather than manufacturability. So what you said was absolutely right, that at the heart of quantum computers are what we call qubits. These are the quantum versions of classical bits, and we understand fairly well how they work. And there are many versions of such qubits, whether it be with superconducting devices, whether it be with cold atoms, with ions or even with photons. In this program we are looking particularly at what can be done to advance the state of the art in the particular context of superconducting qubits. And there, as you said, the huge challenge right now is scalability. How do we go from one or two qubits or even a few dozen qubits to the number of qubits that we actually need for quantum computers to become viable or practical.
Tom Temin And qubits operate mechanically correct? It’s a very tiny thing that’s either here or there, and therefore it has two states. Is that fundamentally what’s going on?
Mukund Vengalatorre That’s the key distinction between a classical bit, which can either be one of two states up or down, or zero or one, and a quantum bit, which can be in a superposition of both zero and one at the same time. And so while that might not seem like a dramatic distinction when you’re just dealing with one bit or one qubit, the essence of being able to put these qubits in superpositions of many different states at the same time has the rather dramatic benefit, as you scale up to the fact that there’s an exponential growth of quantum resources or the available information processing capacity. So each additional qubit that you add to your processor doubles the processing power of your quantum computer. And that has always been the lure of why this would be a transformative new way of computation.
Tom Temin Now, there are companies that have quantum computers and they admit there’s only a couple of dozen or maybe a couple of hundred qubits on them. It’s almost like I remember there was a toy computer when I was a kid that was mechanical and it had three places. You could have a 001 or 010 or 011 or something on it with sliding pieces of metal back and forth. Kind of that’s where they are now. Are these then, such as they are, also supercooled with all the resources that takes.
Mukund Vengalatorre In the context of superconducting qubits or the superconducting quantum computing platforms, that is definitely true. They need these to be operated at temperatures on the order of tens of millikelvin. So that takes a huge amount of infrastructure in terms of how we actually cool these superconducting qubits down. They need dilution fridges, many layers of shielding and these are extremely bulky devices. And so scaling up from, say, like you said, dozens of qubits to the tens of thousands or the hundreds of thousands of qubits that one would actually need to tackle the really hard problems is a enormous challenge right now.
Tom Temin We’re speaking with Dr. Mukund Vengalatorre. He is a program manager in the Defense Science Office at DARPA. So tell us about the project, the challenge, the grants that you have going here for, let’s call it hot computing, hot quantum computing, fair to say hot meaning somewhere above absolute zero.
Mukund Vengalatorre That’s right. That’s a very important point or clarification that needs to be said. When you say hot qubits or warm temperature superconductors, we’re not talking about room temperature. We’re talking about temperatures on the order of a few kelvin. That’s icy, icy cold in normal circumstances, but it’s still warm compared to the current temperatures of such qubits, which are 10 to 20 millikelvin.
Tom Temin But it’s a quantum, pardon the pun, difference in scalability and ability to have something that’s practical.
Mukund Vengalatorre It’s a huge difference. It will make a huge difference in how scalable these quantum processors can become. If we can make the seemingly marginal increase from, say, tens of millikelvin to a few kelvin.
Tom Temin All right. And how are you going about this from a program standpoint? Are you giving grants to institutions to try to develop the science? What’s going on in the program itself?
Mukund Vengalatorre So at a fundamental level, the question we are asking and that also gets to the heart of the name of the program, synthetic quantum nanostructures. So why synthetic? And why nanostructures? And the question we are asking builds upon various insights, including those that have been developed in the past by DARPA. So if I say, what is a nanostructure or what is a metamaterial? These are materials that do not exist in nature. But we know, for instance, in a very classical context, for instance, if I were to say ultralight materials that the picture one has in mind is of these meshes or these foam-like structures, and these do not exist in nature, but these are artificially designed or functionally engineered for specific purposes. So in the context of ultralight materials, the questions one would ask is I want a material that’s extremely strong and I also want a material that is extremely light. If one were to just go down and look in nature for such materials, one can either find strong materials which are heavy or light materials that are fragile. And so it takes kind of a stroke of genius to say, I can indeed combine these seemingly contradictory attributes by functionally engineering synthetic structures. And similarly, we also know of materials, artificial materials or synthetic nanostructures that can modify the flow of sound, that can reflect sound in some wavelengths and not in others. We can do the same thing with light, that we can modify the flow of light. We can cause some colors to be reflected, some colors to be transmitted.
Mukund Vengalatorre The question we are asking in this program is can we engineer such functional quantum materials that can exhibit the kinds of properties that we need of superconducting electronics? And here I am not just restricting attention of this program to quantum or qubits or quantum processors. There are a huge variety of applications that we can harness with such synthetic superconductors, and we are asking the question, can we take existing materials and functionally engineer them to combine seemingly contradictory properties. For instance, extremely robust quantum behavior and higher temperature operation. And if we can do that, not only do we enable a much larger range of scalability for quantum processors or superconducting qubits, we get to build sensors or quantum sensors that are far more sensitive to very weak levels of light. We can process signals at much higher speeds, not gigahertz, but hundreds of gigahertz or even terahertz. And we can start processing these signals at quantum levels of sensitivity. So the aperture opens rather dramatically to what we can do with such superconducting devices once we can functionally engineer these materials.
Tom Temin And how are you going about that discovery of whether these can be made?
Mukund Vengalatorre So we are building on some known insights or recent insights in the physics community that have shown that the current state of nanofabrication and functional engineering is at such a high level of sophistication that we can actually envision being able to do engineered materials at the nanoscale in a certain sense, functionally build up materials from almost an atom by atom level, by combining different materials, different attributes, and harnessing our known knowledge of superconductivity, of knowing how superconductivity works at heart in a class of materials to say, can we push up the temperatures and the functional capabilities of materials or devices that require such superconducting properties.
Tom Temin Well, my question is, who are you asking? Is this going out to academic institutions, laboratories and so forth in the form of grants? And they will try to compete for getting to that answer?
Mukund Vengalatorre That’s exactly right. So this is at such a foundational level where we are saying, we just are posing the question. What if we could functionally engineer new kinds of superconductors? How would we do it? And what are the all the applications that would be engendered by these innovations? And we are asking academia, we’re asking government laboratories and we’re asking industry all to come together to either work together or to pitch their ideas of how they would functionally engineer such superconductors. And the twist in this program that is very important to note, is that we are not just asking these performers or these proposers to develop new materials, we are also asking them to incorporate these materials into actual devices, whether they be qubits, whether they be photon detectors, whether they be amplifiers, quantum amplifiers. And show us that your innovations and your functionally engineered materials do lead to dramatic improvements in these devices.
Tom Temin I guess my question is, given the DARPA context, because ultimately what you do is for defense superiority. How do you keep this knowledge information breakthrough out of the hands of, say, China? Because they’re probably chasing after it also.
Mukund Vengalatorre We’re working at such a fundamental scientific level, especially at the Defense Sciences Office, that of course, down the road there are going to be applications specific work that needs to be done. That would be of a much higher classification and much more sensitive. But right now we are treating this very much like a fundamental academic question. What if we can actually pull this off? And while there are obviously a number of applications that are defense oriented, we could also envision the same devices being employed towards quantum computing for applications like new kinds of materials discovery, new kinds of pharmaceutical discovery. We can envision these kinds of photon detectors being used for medical diagnosis. We can envision these kinds of devices being used for a wide range of applications that have defense, medical or even commercial applications. So at this point, we’re saying let’s just plant some flags here in terms of foundational concepts. And once we know what is truly possible, we can then either go towards more sensitive applications or we can open the horizon for more commercial applications or applications in the context of medicine, materials engineering, materials discovery. There’s a huge, huge range of applications. So at this point we don’t see the need to close the apertures or build walls right when we are at such a beginning or a nascent stage.
Tom Temin And will you know this in three months or ten years or do you have any kind of a cogent timeline?
Mukund Vengalatorre I would be speculating, but I’m reasonably confident that we will know at least what is possible and what would be truly disruptive or transformative within a few years.