By Mark Ritter
In 1981, Nobel Prize winner Richard Feynman challenged computer scientists to develop a new breed of computers based on quantum physics. Ever since then, scientists have been grappling with the difficulty of attaining such a grand challenge.
Employing quantum physics for computation is difficult in part because quantum information is very fragile, requiring the quantum elements to be cooled to near absolute zero temperature and shielded from electromagnetic radiation to minimize errors. This is so immensely different than our current approach to computation that the entire infrastructure of computing must be re-imagined and re-engineered.
Still, the challenges haven’t stopped physicists and computer scientists from trying, and an enormous amount of progress is being made. In fact, I believe we’re entering what will come to be seen as the golden age of quantum computing research.
This is important because quantum computers have the potential to be vastly more powerful than today’s fastest supercomputers.
I oversee a group of scientists and engineers at IBM’s T.J. Watson Research Laboratory who are on the forefront of efforts to create the first true quantum computer.
Today, an important paper written by members of the team was published in the prestigious scientific journal Nature Communications, which outlines two critical advances towards the realization of a practical quantum computer. (The authors are Antonio Corcoles, Easwar Magesan, Srikanth Srinivasan, Andrew Cross, Matthias Steffen, Jay Gambetta and Jerry Chow).
For the first time, they showed the ability to detect and measure two kinds of quantum errors simultaneously, as well as demonstrated a new quantum bit (qubit) circuit design that could successfully scale to create large chips capable of powering computers. These two milestones are very exciting developments–building on IBM’s 30-year history of advancing quantum computing research.
Concurrent with our paper, there are two other articles on related topics from researchers at the University of California Santa Barbara, and the Delft University of Technology, in the Netherlands. This trifecta of scientific achievement shows that the research community is focusing in on the most promising avenues of progress in quantum computing and that advances are now coming at a rapid rate.
Other technology giants like Google and Microsoft have assembled teams of scientists and academics working on quantum computing research. For our part, we’re closely aligned with one of the most respected academic researchers in the field, David DiVincenzo, a professor at RWTH Aachen University in Germany, who was a research staff member of IBM Research from 1985 to 2011. While he was still at IBM, David laid out the criteria that must be met by any practical quantum computer.
Quantum computing works fundamentally differently from today’s computers. 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, a phenomenon known as superposition. For each added qubit, the total number of potential states doubles. Hence, the use of qubits in certain types of computation could enable us to perform calculations exponentially faster than is possible with traditional computers.
In order to perform accurate calculations, qubits must retain their quantum mechanical state long enough that error-correcting codes can be used to suppress errors. Therefore, one of the great challenges is controlling or removing quantum decoherence, the term used for errors in calculations caused by interference from factors such as heat and electromagnetic radiation.
The IBM Research team addressed one aspect of this problem in their experiments. They demonstrated error detection operations using a four-qubit square lattice of superconducting qubits, which is roughly one-quarter-inch square. They were the first to detect and measure the two types of quantum computing errors (bit-flip and phase-flip). Previously, it was only possible to address one type of quantum error or the other. The next step in the field is to correct quantum errors, an important step toward building a large quantum computer.
The square lattice design of our circuit is important for scaling to larger systems of qubits. By being the first to use this configuration, which I believe the rest of the research community will need to adopt, the IBM team will be able to add more qubits to get to a working system. We are already conducting tests of eight qubits in a square lattice in our lab.
I have a photo on my computer hard drive that was taken at the famous First Conference on the Physics of Computation at MIT in 1981. That’s the conference where Feynman challenged his fellow scientists to develop quantum computers. The 60-some attendees, Feynman later wrote, believed that “physics and computation were interdependent at a fundamental level.” The photo shows them posing for a group shot. It’s like a who’s who–including people such as Nobel Prize winners Feynman and John Wheeler, and Conrad Zuse, a German computer pioneer. The group included three IBMers, John Cocke, inventor of the RISC architecture, Charles Bennett, a pioneer in quantum encryption technology, and Rolf Landauer, a theorist in the physics of information, who helped organize the meeting.
I keep the photo as a reminder of the potential for multidisciplinary groups of brilliant people to focus their collective intelligence on the world’s most challenging problems. I count among them the Manhattan Project, the Apollo program and this– the quest to develop quantum computers.
In each case, the goal seemed at first to be nearly impossible to achieve. But, again and again, incredible groups of people manage to prove the naysayers wrong. The quantum computing quest is still a work in progress. But I have every confidence in IBM’s exceptional team, and believe that we will be the first to develop practical quantum computers–bringing tremendous benefits for individuals, society and the future of the planet.