Earlier this year, NASA, in partnership with Google, acquired the world's largest quantum computer. But just what does the space agency plan to do with a device with such revolutionary potential?
NASA is currently looking at three very basic applications, including one that would serve as a day-planner for busy astronauts who are up in orbit.
"If you're trying to schedule or plan a whole bunch of tasks on the International Space Station, you can do certain tasks only if certain preconditions are met," he explains. "And after you perform the task you end up in another state where you may or may not be able to perform another task. So that's considered a hard optimization problem that a quantum system could potentially solve."
They're also looking to schedule jobs on supercomputers. And in fact, NASA Ames is responsible for running the agency's primary supercomputing facility. No doubt, at any instance of time they've got hundreds of individual jobs running on a supercomputer, while many others are waiting for their turn. A very difficult scenario would involve a job waiting to run — one that requires, say, 500 nodes — on a supercomputer with 1,000 nodes available.
"Which 500 of these 1,000 nodes should we pick to run the job?," he asks. "It's a very difficult scheduling problem."
Another important application is the Kepler search for exoplanets. NASA astronomers use their various telescopes to look at light curves to understand whether any noticeable dimming represents a potential exoplanet as it moves across its host star. This is a massive search problem — one that D-Wave could conceivably help with.
"These are the types of applications that we're trying to run," says Biswas. "We're doing it on our D-Wave system, which is the largest in the world, but it's still not large enough to solve the really hard real world problems. But by tackling the smaller problems, we can extrapolate to how a larger problem could be solved on a larger system." "But each of these images may be at a certain wavelength, and you may not get all the information from the image," he explains. "One of the challenges there is what's called data fusion, where you try to get multiple images and somehow fuse them in some smart way so that you can garner information from a fused image that you couldn't get from a single image.
And at NASA's Ames Research Center in Silicon Valley, Biswas's team runs the supercomputers that power a significant portion of NASA's endeavors, both public and commercial.
"We see quantum computing as a natural extension of our supercomputing efforts," he told me. "In fact, our current belief is that the D-WAVE system and other quantum computers that might come out in the next few years are all going to behave as attached processors to classical silicon computers."
Which is actually quite amazing. So in the future, when a user wants to solve a large problem, they would interact with their usual computer, while certain aspects would be handed over to the quantum computer. After performing the calculation, like an optimization problem, it would send the solution back to the traditional silicon-based machine. It'll be like putting your desktop PC on steroids.
"Just so we're clear, the D-Wave system is just one of many ways to leverage the effects of quantum physics," he told me. "But in order to use any quantum system, the first thing you need to have is a problem mapped in QUBO form." A QUBO form, which stands for a Quadratic Unconstrained Binary Optimization form, is a mathematical representation of any optimization problem that needs to be solved. At this time — and as far as we know — every single quantum computer requires that the input be in QUBO form.
"And that's a serious problem," says Biswas, "because there's no known recipe to devise a problem and then map it into QUBO form. But once we get a QUBO form — which is a graph representation of the problem — we can embed this onto the architecture of the D-Wave machine."
The D-Wave processors run 512 qubits which are made up of 64 unit cells. Each unit cell is made up of 8 qubits. And each qubit is made up of a bipartite graph, so there are four quibits on the left and four on the right. Each of the four qubits are connected to the ones on the right and vice-versa. But it's not a fully connected graph.
"So what happens therefore, is after you take your problem in QUBO form and you try to embed it into the D-WAVE machine it's not a universal quantum computer. It's not like you have computer keyboard and you can just tell the machine what to do." Essentially, the machine becomes dedicated to the task outlined by the QUBO form — a limitation that could impact scalability.