Volume 3, Issue 3 April 2003

2003
2002
2001

The science-fiction fantasy of nanotechnology — building novel structures, devices, and materials at the atomic or molecular scale — is becoming a reality. For the great potential of nanoscience and nanotechnology to be fully realized, however, research efforts must cross many disciplines, from electrical engineering, mechanical engineering, materials science, and computer science to bioengineering, chemistry, and physics. Nowhere is this cross-disciplinary approach fostered more than at UC Berkeley. Each month, Lab Notes is proud to present the work of nanotechnology researchers from the College of Engineering and our collaborators across the campus. A Quantum Leap In Computing by David Pescovitz Printer-friendly version This diagram depicts a system of Qubits, the building blocks of quantum computers. Courtesy KB Whaley With quantum processors hyped as the next big thing in post-silicon computers, UC Berkeley researchers have received a National Science Foundation (NSF) grant to prove that the seemingly far-fetched technology will actually work. By harnessing the unusual properties of quantum physics, quantum computers could potentially perform a billion times faster than today's silicon-based processors. For instance, quantum computers could be used to simulate complex biological phenomenon like protein folding, the process by which proteins assemble themselves to carry out specific functions. Understanding protein folding could lead to cures for diseases such as Alzheimer's and cystic fibrosis. In the nearer term, the fabrication of extremely accurate quantum clocks could dramatically improve the precision of radar and the Global Positioning System (GPS). "Quantum computing is still somewhat speculative, so we want to understand what is likely to make this a winning technology," says Shankar Sastry, professor and chair of the Department of Electrical Engineering and Computer Sciences and an investigator on the project. Shankar Sastry is a former director of the Information Technology Office of the Defense Advanced Research Projects Agency (DARPA). Angela Privin photo The $4.5 million NSF grant supports a cross-disciplinary research effort by the College of Engineering, the Physics Department, and the College of Chemistry. Sastry is collaborating with project leader K. Brigitta Whaley, professor of chemistry, on the theory and control of quantum computers. Meanwhile, the experimental physicists — J.C. Seamus Davis, Michael Crommie, Alex Zettl, and John Clarke — are investigating new kinds of qubits. In recent years, researchers have built quantum computers that employ seven quantum bits, or qubits, but the technology is not easily scalable or robust enough to build powerful quantum nanoprocessors with thousands of qubits. Qubits are the fundamental building block of quantum computers, the equivalent of the binary 0 or 1 bits of digital computers. The direction of an electron's spin could be used as a qubit, as could a "quantum dot," a particle whose properties change with the addition or subtraction of an electron. The power of quantum computers lies in a qubit's ability to exist in a one or zero state, or a superposition that is somewhere in the middle, or, oddly, both at one time. This quantum weirdness is what enables quantum computers to process so many data at once. Essentially, each qubit represents two values at one time. As more qubits are strung together, the power of the quantum processor grows exponentially. Additionally, each qubit is entangled with every other one so that manipulating one qubit affects all of them. Einstein called this phenomenon "spooky action at a distance," and scientists still don't understand how it's possible. According to Sastry, quantum entanglement could be exploited to secure the Internet's optical backbone. If photons traveled through the network entangled in quantum states, he says, "the data would be absolutely unsnoopable," or secure from spying eyes. "The problem faced with quantum (technology) though, is that it's impossible to isolate a quantum bit from what's around it," Sastry says. Will a multidisciplinary approach help make quantum processors the next big thing? We want to hear from you... Basically, interfering with the subatomic particle in any way, including reading its state, kills the superposition. This is called decoherence. Sastry and Whaley are developing new procedures based in traditional control theory to correct for decoherence errors. "Decoherence will cause signal degradation over a period of time," Sastry says. "So you need good error correction to allow for that degradation." While the NSF-funded team studies the materials, circuits, and individual devices necessary to build a quantum processor, computer science professor John Kubiatowicz is collaborating with researchers from UC Davis and MIT to combine all the elements together. Sponsored by the Defense Advanced Research Projects Agency (DARPA), the Quantum Architecture Research Center is charged with developing architectures and applications for quantum computers. Also in the computer science division, professor Umesh Vazirani develops novel quantum algorithms so the computers his colleagues are developing can eventually be programmed to tackle useful tasks. The more expertise and cross-pollination, the better, Sastry says. Indeed, a project of this scale with so much disruptive potential requires a true multidisciplinary team working in concert. "In silicon, someone working on one layer of a computer can pretty much forget about the other stuff," he says. "But with quantum computing, the algorithms, the architecture and everything else all interact with the physics." NSF Award Abstract: Exploration and Control of Condensed Matter Qubits KB Whaley Group: Quantum Information Processing Quantum Architecture Research Center "NSF grant to UC Berkeley will fund exploration of new types of quantum computers" by Robert Sanders (Campus Media Relations) Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow. Editor, Director of Public Affairs: Teresa Moore Writer, Researcher: David Pescovitz Designer: Robyn Altman Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu. © 2003 UC Regents. Updated 4/4/03.