By Steve Hamm
Patience is one of the most important virtues a researcher can possess, but some scientific pursuits require an almost preternatural calm in the face of monumental challenges. Case in point: quantum computing.
Scientists have been trying to grasp this holy grail of computing ever since Nobel Prize-winning physicist Richard Feynman in 1981 challenged the scientific community to build computers based on quantum mechanics. Matthias Steffen, the manager of an experimental quantum computing project at IBM Research, believes the key to persevering in a project like this is keeping an open mind. ” You can’t stubbornly keep pursuing a path because you’re invested in it personally,” he says. “Take a breather, and be open to making changes in your approach–potentially drastically”
The IBM Research team has produced a series of breakthroughs that have helped push quantum computing research to a turning point. Steffen and other scientists are convinced that enough progress has been made that they can now start creating small but meaningful computing systems based on the science. And, indeed, flexibility has been one of the key recurring themes in IBM Research’s pursuit of the quantum computing riddle.
For Matthias, openness to outside influences comes naturally since he has lived in Europe, Asia and the United States.“I’ve seen a lot of different cultures, and met a lot of people with different backgrounds. It helped me realize that there are many ways of getting something done,” he says.
As an undergraduate physics student at Emory University in the late 1990s, Matthias saw the end of Moore’s Law approaching. But he had no idea what would succeed conventional semiconductor technology until, as a senior, he read an article in the magazine Physics Today about quantum computing. That was the solution, he decided. It became his quest. He went on to do research in quantum computing in graduate school, not as a theoretical exercise but because he wanted to use his knowledge to build something completely new.
Quantum computing may have huge implications for the technology world, but it is not clear how far reaching its applications will be. One likely target is the field of data encryption, because quantum computers can, theoretically, factor large numbers like those used for making sensitive data undecipherable to prying eyes. But the technology will potentially have other uses, as well. For instance, it might be useful in helping people to understand the interactions of complex systems of systems that underlie everything from the human body to cities to the global financial industry.
Quantum computing works fundamentally differently from today’s computing. A traditional computer makes use of bits, where each bit represents either a one or a zero. In contrast, a quantum bit, or qubit, can represent a one, a zero, or both at once. Therefore, two qubits can be in the states 00, 01,10 and 11 at the same time. For each added qubit, the total number of potential states doubles. Hence, the use of qubits in certain kinds of computation could enable us to process exponentially larger quantities of data than is possible with the same number of conventional bits.
A little more than a decade ago, a team at IBM Research – Almaden, in San Jose, Calif., explored an approach to quantum computing called liquid state nuclear magnetic resonance quantum computing. (Matthias, while an electrical engineering PhD candidate at Stanford University, was a junior member of the team.) Besides being a mouthful, it turned out that liquid state NMR had no clear path towards a practical quantum computer. The team’s leaders concluded after several years of work that it wouldn’t take them to a major breakthrough, and the project wound down.
IBM’s research into quantum computing continued at the research lab in Yorktown Heights, New York. The focus was on superconducting qubits, one of a handful of approaches that were beginning to seem most promising.
Yet when Matthias joined IBM Research in 2006, the quantum computing project in Yorktown Heights was stuck. The approach they were taking wasn’t yielding much progress. After much debate, the group decided to rethink everything. They’d start again from scratch. What should their qubits look like? How would they manipulate them? After pressing the reset button, they decided on a different approach, which included a new technique for designing qubits that was based on the best understanding at the time. The field was changing rapidly, and, as a result, Matthias says, the team’s approach had to change with it.
Their immediate challenge at the time was dealing with error rates. In order to perform accurate calculations, qubits must retain their quantum mechanical properties—the delicate state of being both 1 and 0 long enough to suppress error rates. So one of the great challenges is controlling or removing quantum decoherence, the creation of errors in calculations caused by interference from factors such as heat and electro-magnetic waves.
The change of direction ultimately led to the group to the approach they’re taking now. They decided to use techniques in which qubits are coupled to resonators (an electronic equivalent of a pendulum), in hopes of steadily extending the amount of time during which the qubits are stable.
They based one aspect of their work on some pioneering research by a group of at Yale University. The Yale group placed qubits in small containers called three-dimensional microwave cavities, which shield them from external interference. In IBM’s labs, the containers measure 1 inch by ½ inch by 1/2 inch, so, relative to the world of microelectronics, they’re huge. But, as with the early evolution of conventional microelectronics, the researchers are doing experiments on a large scale with the expectation that their inventions will ultimately be shrunk down to the microscopic level.
Using these and other techniques, in three years they produced a 10,000-fold improvement in the performance of their qubits. The team achieved a major milestone in early 2012 when they demonstrated that they could extend the amount of time their qubits retain their quantum states up to 100 microseconds—long enough, theoretically, to correct errors and perform dependable calculations. In order to be practical, however, the lifetimes of quantum states need to be improved by another 10x to 100x.
Today, the team is hand-building containers from small blocks of copper and aluminum in the lab’s machine shop. They gingerly insert single qubits made of layers of aluminum and aluminum oxide onto tiny chips of sapphire. Then they place the chips within the cavities, several qubits per container, and connect them to wires. These tiny devices won’t win any supercomputing performance contests. The best they can do is simple addition. But it’s a start. The goal now is to string together a dozen calculating qubits, then 100, and, someday, one million qubits capable of performing useful computing tasks.
They still have to make further improvements in error correction rates, but they now have a quantum device technology that they believe will be successful over the long haul. So they’re beginning to address the array of quantum computing challenges holistically. The goal is to build an entire computing system by combining a laundry list of capabilities—ranging from the design of the qubits themselves to the way they’re combined to the way the computing process is launched and managed. It’s a tricky endeavor. When they optimize one aspect of the system, they run the risk of degrading others. So they must find just the right balance.
Their primary tool for performing this work is a dilution refrigerator. It’s a cylindrical apparatus about the size of a small car that’s installed in a small room within the lab. The shell of the machine lifts to reveal a collection of smaller cylindrical shields and electrical sensors and connectors. The researchers position their microwave cavities containing qubits within the small cylinders, close the refrigerator, leave the room, flip the switch on the refrigerator and wait approximately 24 hours for the interior of the apparatus to reach a decidedly chilly temperature—10 millidegrees Kelvin, near absolute zero. (That’s about -459 degrees Fahrenheit.)
Obviously, we won’t be able to chill entire, room-size quantum computers down to this extreme temperature, and that’s just one of many signs that the scientific community still has a very long way to go to realize Feynman’s dream. But, at last, steady progress is being made, and there’s no obvious reason why this can’t work. It’s impossible to predict the exact path that discovery will take, or how long it will take. But this much is clear: an incredibly disruptive technology is busy being born. And nobody knows where it will take us.
Matthias is optimistic about the prospects. He thinks computer scientists will produce functional quantum computers with useful applications in 15 to 20 years, if everything goes smoothly. And he’s determined to be one of them.