The Subatomic Race to Harness Quantum Science
US, China are betting millions on the promise of this newish field, but the real-world potential remains a mystery.
An assortment of super powers awaits the superpower that harnesses quantum science: unhackable communications, radars that see underground, supercomputers that make today’s biggest machines look like first-generation Ataris. But which of those goals are achievable in the near future, and at what cost?
Earlier this summer, the Pentagon announced a $45 million research effort into quantum networking. Meanwhile, China hopes to complete construction of the world’s largest quantum communication network and become the first nation to put a quantum communications satellite into orbit. But other military-funded research has suggested that quantum comms and cryptography may prove too complicated to warrant the effort, while quantum computing will remain out of reach for a decade or more. (Some argue that's being very optimistic.)
All of this power, and all of this hype, emerges from a source almost unfathomably small: atomic and subatomic particles that behave differently than larger objects, especially at very cold temperatures. It’s enormously difficult even to study quantum objects; simply observing them generally changes their behavior.
The Holy Grail of applied quantum science is quantum computation, which is as different from regular computers as humans are from jellyfish. Whereas conventional computing uses electrical impulses running through transistors to manipulate bits, or binary values of one or zero, quantum machines track the strange behavior of ultracold atoms that can exist in two states at once — a one, a zero, or both. If you’ve got two qubits in the same so-called superposition, you have what’s called an entanglement gate. They’re atomically linked even if they’re miles apart. And this opens up the possibility of massive parallel calculating. What would you use that for? Think about cracking a code: you try one combination after another after another. But if you can try all the possible combos at once, you arrive at the solution instantly.
“Much like autonomy, quantum sciences is an area that could yield fundamental changes in military capabilities,” Defense Undersecretary Frank Kendall said at a Defense Department Lab day in June. “Examples include non-GPS [position, navigation, and timing], remote detection of submarines, remote mapping of tunnels and underground facilities … secure wireless communications and many others.”
Last November, the government of China announced two ambitious goals: the construction of a 1,240-mile quantum computer network stretching from Beijing to Shanghai, set to go live in 2016; and the launch of a quantum communications satellite. As of February, both projects were on track, according to Wang Jianyu, deputy director of the Chinese Academy of Science’s (CAS) Shanghai branch, who spoke at a conference.
In June, U.S. Deputy Defense Secretary Robert Work announced a $45 million quantum science research effort that would bring together the Air Force, Army, and Navy research labs to create a scalable quantum network with memory — on in which a quantum state is maintained without a loss of coherence. “This team is trying to figure out how to encrypt and then transmit information across long-range military networks for the war-fighter in a provably secure and robust fashion,” said Work. Such a network, which would allow quantum data to flow between physically separate systems, could support further research on quantum computing and quantum cryptography.
The United States does about one-quarter of the research and development in quantum science right now, at least as measured by articles in scientific journals, says Werner J.A. Dahm, who chairs the Air Force’s Scientific Advisory Board. Dahm’s board recently wrapped up a study of the field and its potential. Among its findings: some quantum-enabled tools may not be enough of an improvement over current methods to be worth the difficulty of developing them.
One potentially over-hyped area of investment is quantum encryption. It works like regular key distribution, with sender and receiver able to see the message only after they have exchanged a secret cryptographic key. But unlike some cryptographic solutions, no third party can penetrate it without being detected. Because subatomic particles change when they are viewed, any attempt to intercept the message would corrupt it in a conspicuous way, allowing sender and receiver to know immediately, and with certainty, that the message had been compromised.
“Rather remarkably, the study found that the Air Force has other alternatives for enhancing security of communications that don’t have as much of a complexity burden associated with them,” Dahm told reporters recently. “Most of what the study saw in the quantum area with regard to communications, the Air Force has equally good or better alternatives with other approaches.”
But other areas are more promising. In the near term, Dahm said, the most important thing quantum science can do for the Air Force is help it leave behind the expensive and aging Global Positioning System.
“These quantum navigation systems can allow very, very high accuracy and they can’t be jammed,” he said. “The drift rates are much lower than traditional [Inertial Measurement Units] have. That gives the Air Force very important utility for operating in a GPS-denied environment.”
Such positioning systems “are making remarkable progress and could be brought to a level of maturity that they would be valuable to the Air Force at a time scale that’s of interest to the Air Force. It’s not 30 or 50 years out,” he said.
Indeed, prototype quantum navigation and timing systems already exist, but they’re too large for many airplanes, missiles, and drones. That’s because they take advantage of the behaviors of atoms when they’re at their lowest level of energy, a state achievable only at incredibly cold temperatures — in some cases, a billion times colder than outer space. Cooling atoms to those depths requires lasers and energy. “It’s now a matter of shrinking down, and the study actually recommends the Air Force take the lead on that and invest, at a modest level, in miniaturizing these kinds of systems,” Dahm said.
Similarly, large quantum-enabled sensors already exist for looking underground. Oil and gas companies use quantum sensing to map subterranean cavities and hydrocarbon deposits. Very small changes in mass composition can have gravitational effects, far too subtle for today’s instruments to sense, but detectable at the quantum level. If such sensors could be made smaller and better, militaries might use them to pinpoint underground bunkers — or spot enemy submarines. But gravitational sensing for the military will be limited by how close sensors can get to their potential targets, Dahm said.
The government has been funding quantum computer research for more than a decade, primarily for code-breaking. Last year, the Washington Post reported that the NSA was spending $80 million on a program called Penetrating Hard Targets to build a quantum system to crack the world’s toughest encryption standards.
But code-breaking isn’t the only area massive parallel-processing could be useful. “There are lots of Air Force problems to which quantum computing could be applied,” said Dahm. “Think about an aircraft and trying to compute…a signature in the [radio frequency] domain, let’s say. That is a massive computational problem. We throw large amounts of traditional computing power at those types of problems. If we could do that with a quantum computer you would be able to get it to a level of precision where you almost wouldn’t need a test range.”
But the barriers to real, provable, and practical quantum computing remain seemingly insurmountable. Even as quantum computing companies such as D-Wave claim to have achieved 512-qubit entanglement, the question of how to even to write code for a quantum computer remains a topic mostly of mystery.
“While the hardware side of quantum computing has made substantial progress, even if you had a quantum computer existing today, you can’t run regular software on a quantum computer. It doesn’t work that way. A quantum computer is not just a regular computer. It’s fundamentally different. Forget the software; the algorithms themselves on which the software is based have to be completely different,” said Dahm.
It’s an area replete with promise, but little hope of near-term payoff. The Air Force science board study recommends “a modest, continued effort with a focus on the software rather than the hardware.”
Even with world powers in the running, then, the race to harness quantum science will likely be a slow and steady one.