The field of quantum physics, a century-old science, which found that particles have unique and unexpected properties at the smallest scale, is now at the cutting edge of research into revolutionary new technologies that could dramatically impact U.S. defense and national security. From gravitational sensors that can detect submarines underwater to next-generation computing, the Cipher Brief’s Fritz Lodge talked to Dr. Stephen Jordan, a physicist at the National Institute of Standards and Technology (NIST), about the race to turn theoretical quantum properties into reality.
The Cipher Brief: For the layman, what is quantum physics and how does it inform the creation of new technologies that we are now seeing emerge?
Stephen P. Jordan: Normally, when we see objects they’re in one specific place, we see them do something and we can attribute that to a cause and effect.
All that goes out the window at the quantum scale. The idea behind quantum information technologies is to take these weird behaviors that we see at the quantum scale and, instead of seeing them as nuisances, put them to work in ways that we can’t with ordinary classical systems.
One of the most dramatic and exciting things we have learned is that we should, at least theoretically, be able to do is solve certain computational problems exponentially faster than we can classically.
TCB: How does this work, and what quantum technologies could be most useful in the defense and national security context?
Jordan: It’s very difficult to get this to work in practice because these strange quantum states where things are in more than one state at a time, which we call superposition, are actually very fragile. It’s hard to maintain these superpositions, and that’s why we don’t see them in everyday life.
You have to isolate your systems very carefully, you have to cool them to unimaginably cold temperatures and try to isolate them from every source of noise, and this is a very difficult quest that’s being pursued in laboratories around the world in government, private industries, and a number of different settings. But if someone gets it to work, these machines will enable us to do certain things much much faster.
One of the capabilities which really captured people’s attention was factoring numbers into their prime factors. That is of great significance to security because if you could do that you could break all of the commonly used, widely deployed cryptographic systems. These are useful for things like e-commerce and a wide variety of national security applications.
Right now, there’s a big effort to develop next-generation cryptographic systems which can’t be broken by quantum computers because they’re not based on factoring. That’s one thing that we actually do at NIST.
TCB: How exactly does this next-generation cryptography work?
Jordan: There are several candidates. Each one is based on a different hard computational problem. One class of crypto systems is based on a geometric problem, which is finding short lattice factors in very high dimensional lattices. So you might have some regularly spaced set of points, kind of like tiling on a floor or atoms in a crystal, except it’s in maybe 2000-dimensional space. That’s one example. Another example would be creating a large system of quadratic equations that you need to solve all at once.
In total, there are probably about five alternate tools like this that you could use to rebuild cryptography from the ground up once the tools that we’re using right now are broken by quantum computers.
TCB: Is the technique in which photons are used to send encrypted messages, one of these tools?
Jordan: Yes, so this is a different but related thing. What I’ve mentioned so far are crypto systems that use the same communications network that we already have. This would just be like a software update for your browser.
There is also something called quantum cryptography – or more accurately quantum-key distribution – and in that case you often use the polarization state of photons to transmit your information in a specially designed way so that if anyone eavesdrops on your conversation, you would be able to detect that and stop talking.
TCB: Are people already thinking of ways to get around this kind of quantum cryptography?
Jordan: There is a professor at the University of Waterloo named Vadim Makarov who calls himself the quantum hacker.
These quantum-key distribution devices are actually developed to a higher maturity level than quantum computing technology in some sense. These are things that you can actually buy, but they’re limited in range to maybe 100 kilometers or so. What this guy does is buy these machines, tinker around in his lab with them, and find ways to defeat them, like shining bright lasers into the fiber, spoofing the sensor, and things like that. He exploits the nitty gritty of how the hardware is built to crack the system.
It’s kind of a back and forth. In principle, this kind of messaging should be completely secure, but if it’s not implemented quite right then there are side channel attacks that hackers can use to detect information leaking out of other channels that you didn’t think about when you set up the system.
There’s a funny anecdote about this. The first demonstration of quantum-key distribution was built at IBM, and it implemented the protocol correctly and could transmit this secure information over a distance of one foot or something like that. But the power supply that they used was a cheap one – they didn’t have funding for this – and it would buzz when you transmitted your data, and it would make a different tone when you transmitted a one versus a zero. So anyone listening could hear the message.
TCB: Where is all this researching happening? How far along is the United States compared to potential adversaries like China?
Jordan: The U.S. is pretty strong in quantum information science and technology, but by no means is it unambiguously dominant. There is a lot of stuff going on in Europe, and there is also a lot of spending going on in China.
When I started studying this around 15 years ago, there was not much coming out of China that was worth reading, but that has changed. They have really come a long way in a short time and their trajectory is strongly upwards. China is getting quite serious in this field. They have actually demonstrated quantum cryptography using satellites, which is pretty impressive, and now they’re starting to invest in quantum computing as well.
TCB: What is the advantage of the satellite cryptography?
Jordan: So, if you do quantum-key distribution over optical fiber, it’s limited to about 100 kilometers. But if you do it just through the air by projecting lasers through a telescope essentially, then you can actually transmit thousands of kilometers.
TCB: What is the most exciting aspect of this quantum revolution to you? What is the most threatening or challenging?
Jordan: I am personally the most excited about quantum computing. Quantum information encompasses the computing side, the communications side (like quantum cryptography), and also sensors – things like very sensitive accelerometers and gyroscopes and so on…
TCB: And how could those be used?
Jordan: Well, for example, you could try to do inertial navigation with them. Or you could try to use them to detect things underground – by measuring for gravitational anomalies. That’s something that has a lot of applications both for military purposes and in industry.
But the change that I find so dramatic is on the computing side. It’s just crazy how big these speed ups could be, and it remains very imperfectly understood which problems quantum computers will speed up and which ones will not be highly affected. For a lot of things, a regular classical computer works just fine and a quantum computer doesn’t help. So it’s very exciting to search around and see what works.
The thing that is the most nerve-wracking is trying to get these post-quantum crypto systems ready in time for quantum computers. It’s not that easy to check them carefully, make sure there’s no bugs, make sure there’s no attacks on them we haven’t thought of yet, get them standardized and widely deployed, etc. All of that is an uphill battle.
TCB: And if that doesn’t happen in time then all current cryptography could become essentially irrelevant?
Jordan: Yes, that’s right.
Presumably, quantum computers will initially be very expensive and held only by a few, but even so it’s worrying.
