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National Security Drives Quantum Computer Research

October 2010
By George I. Seffers, SIGNAL Magazine
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Although quantum computers will look nothing like cryptology machines from previous generations, they may be just as big, or even bigger.

Government agencies and universities are allied on potential encryption powerhouse.

No one knows yet what a working quantum computer will look like, how long it will take to develop or how many functions it will perform, but one thing is almost certain—it will be critical to national security. If such a computer is ever built, it likely will be the most powerful machine on the planet for encrypting or decrypting information, easily capable of cracking current encryption codes used by the military, intelligence agencies and commercial entities such as the banking and financial services industry.

This is largely why a host of U.S. government agencies is teamed with universities across the country and internationally to crack the science code that will make quantum computers viable. Participating federal organizations include the National Security Agency (NSA), U.S. Army Research Office (ARO), Defense Advanced Research Projects Agency, Intelligence Advanced Research Projects Activity, Air Force Office of Scientific Research, Office of Naval Research, Sandia National Laboratories, the Department of Energy’s Los Alamos National Laboratory and the National Institute of Standards and Technology (NIST).

“Because NSA is responsible for the protection of national security systems, the computer systems of the Department of Defense and intelligence community, we must understand the likelihood of development of—and the threat posed by—quantum computers so that we can help to protect against that,” explains Barry Barker, the NSA technical director for quantum computing.

Peter Shor, currently a professor of applied mathematics at the Massachusetts Institute of Technology, rocked the encryption world in 1994 while working at Bell Laboratories. It was there that he developed what has since become known as Shor’s algorithm, which demonstrated that quantum computers potentially could perform calculations at far greater speeds than conventional computers and could, therefore, pose a major threat to conventional encryption methods. A conventional computer relies on the laws of classical physics, but a quantum computer will rely on the laws of quantum physics, or physics at the atomic or subatomic level. Quantum computer experiments use the ability of quantum bits, or qubits, such as a collection of atoms, to be in an unlimited number of states simultaneously. Whereas conventional computer bits come either in ones or twos, a qubit can be the equivalent of both a one and a two at the same time. In theory, this capability will allow the quantum computer to perform many different computations simultaneously.

The NSA and the ARO, a part of the Army Research Laboratory, recently published a broad agency announcement seeking proposals for basic and applied research to advance quantum computing technology. Proposals were delivered in mid-July, but the government had no set schedule for awarding contracts. The NSA and the ARO are interested in three key research areas: robust, solid-state qubits and related technologies; short-to-medium-range quantum information transfer in solid-state systems; and ideas, methods and procedures for the verification and validation of quantum computing components. These three areas of research are roughly equivalent to those that were needed for conventional computers 50 years ago, Barker states.

“If you were to look at classical computing capability, these three things form the nucleus of what you have to have in order to develop a computing technology. You need to have some sort of memory storage, you need to be able to move that information around, and then when you get ready to actually build your computer, you need a way to test its components to make sure they’re going to function the way you think they’re going to function,” Barker explains.

Inherent in all three research areas is the holy grail of quantum computing science—solving the decoherence problem. When a qubit interacts with its environment, its ability to be in an unlimited number of states collapses. Among other environmental variables, minuscule sound vibrations can cause that collapse. If the qubits suffer too much decoherence before completing a calculation, the information is irretrievably lost. A viable quantum computer most likely will never be built until the decoherence issue is resolved.

“Quantum decoherence is buried in all three [research] topics. When we say that we want a robust qubit, that means you have to solve the decoherence problem for those qubits. The same holds true when you move them around, and part of the verification and validation topic is understanding the limits caused by decoherence. So decoherence underlies all three areas,” Barker explains. “You have to understand decoherence in a lot of different arenas in order to progress the field as a whole. That’s one of the big problems everyone is working on. Universities around the country and around the world are all trying to understand the causes of decoherence and how to minimize that in a quantum computer.”

 

A conceptual image portrays the future Laboratory for Physical Sciences at the University of Maryland College Park, which will house the basement laboratories of the Laboratory for Advanced Quantum Science.

Conventional computer technology advanced rapidly in recent decades in large part because the commercial sector saw a wide range of possible uses—and therefore, potential profits—and invested heavily. Intel cofounder Gordon E. Moore pointed out decades ago that computer processing power had doubled roughly every two years. That trend, now known as Moore’s law, has continued to this day and likely will continue into the near future, according to experts.

Although quantum computing researchers have made strides in recent decades, the technology has not advanced as rapidly as conventional computing in part because researchers believe potential uses, and potential profits, will be more limited, so industry does not have the same incentive to invest. But government resources and the sheer thirst for knowledge have driven scientists to investigate quantum computing to the point that it has become a much more robust and dynamic field of study. The field is evolving rapidly into one of the most active research areas of modern science, attracting substantial funding internationally for academic institutions, national laboratories and major industrial research centers. Programs are underway in the United States, Australia, the European Union and its member nations, and in other major industrial nations. Scientists from a variety of disciplines are using a diverse range of experimental approaches to pursue answers to the fundamental questions involved in quantum computing.

“The best news story is that quantum computing has become a vigorous research field and that we can work with and exploit quantum mechanics,” says T.R. Govindan, program manager for the Quantum Information Science Physics Division at the ARO.

Barker echoes that sentiment: “We started working in this field in the mid-1990s. This was then a purely mathematical conception, and it’s now progressed to a much more elaborate field of science. We aren’t the only group to play a role in that, but we’re one of the groups, both in funding research with universities over the years and doing some of the research ourselves. We’ve played a substantial role in advancing this field,” Barker says.

The NSA works closely with the University of Maryland’s Laboratory for Physical Sciences, where physicists are actively researching several areas, including silicon-based quantum computing. Research in this area focuses on the future of superconducting and silicon-based qubits. Silicon-based quantum computing is a topic of intense research worldwide because of the relative stability, or coherence times, of qubits in silicon and the potential for these qubits to be incorporated into future silicon devices using technology developed for conventional electronics.

Meanwhile, physicists at NIST announced in July that they recently had demonstrated a device for trapping a single ion, an electrically charged atom formed by the loss or gain of one or more electrons. The ion trap uses a built-in optical fiber that collects light emitted by a single ion, allowing quantum information stored in the ions to be measured. The advance may simplify quantum computer design and may be a significant step toward swapping information between matter and light in future quantum networks. The one-millimeter-square device uses ions as qubits to store information and can position an ion 80 to 100 micrometers from an optical fiber. More conventional ion traps use relatively large external lenses located about five centimeters away from the ions—about 500 times farther away than the optical fiber.

In another recent development, University of Maryland researchers within the Joint Quantum Institute revealed in July that they used a laser to convert qubits from a state of one to a state of zero in less than 50 trillionths of a second—more than 10,000 times faster than previous accomplishments with similar systems—and they did so with a 99 percent reliability rate.

NIST awarded the Joint Quantum Institute $10.3 million earlier this year for the construction of a state-of-the art Laboratory for Advanced Quantum Science, which is scheduled for completion in 2013. In July the institute was awarded a Defense Department contract valued at several million dollars to investigate “atomtronics,” a new field of study that seeks to create analogues of electronic devices, such as transistors and diodes, by using “ultracold” atoms trapped in optical lattices formed by intersecting laser beams. That award came on top of two similar contracts the institute received last year to study quantum optical circuits and ultracold polar molecules.

“Some of these experiments occur at temperatures about a hundred times colder than interstellar space. At those temperatures, air is solid,” Barker says. “This is one of the reasons mom and pop will not have one of these in their house for doing word processing.” He adds that no one knows what a quantum computer will look like, but he speculates it probably will be housed in a laboratory or environmentally controlled building and likely will not fit on a desktop. “In general, it’s going to be fairly large. It will be one of the most complex devices ever built. It’s going to be the size of a room, or at least a large fraction of a room, and it will probably have some sort of vacuum chamber, so it will have vacuum pumps attached to it, and it may have cryogenic operation, meaning temperatures 400 degrees below zero, for example,” he explains.

Barker also says no one can predict how long it will take to build a quantum computer—or if it even can be done. “There are so many fundamental scientific challenges that have to be overcome, we can’t predict when, or if, the scientific community is going to overcome these problems, but most guesses are—and calling it a ‘guess’ is a more accurate term than calling it an ‘estimate’—the guess is that a practical quantum computer is still many decades away. If you think about the timeline from building an individual transistor in the 1940s or early 1950s to modern-day computers, we’re talking about 50 years.”

For all the advancements, quantum computer research is still in its infancy. “This is very far out research. We’re still doing fundamental science in quantum computing. We’re not just trying to build another widget. We’re trying to build a new class of widgets,” Barker says.

WEB RESOURCES
NSA cryptology: www.nsa.gov/about/faqs/heritage_of_cryptology.shtml
NIST Physics Laboratory: http://qubit.nist.gov/
University of Maryland Laboratory for Physical Sciences: www.lps.umd.edu/
Los Alamos quantum cryptography: www.lanl.gov/science/centers/quantum/cryptography.shtml