PHYSICS ILLINOIS NEWS THE DEPARTMENT OF PHYSICS AT THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN • 2006 NUMBER 1 Quantum Computing without “Computing” BY JAMES E. KLOEPPEL computer did not run (O. Hosten, et al., Nature 439, 949–952 [2006]). y combining quantum Quantum computers have the Bcomputation and quantum potential for solving certain types of interrogation, Bardeen Professor of problems much faster than classical Physics Paul Kwiat and his group have computers. Speed and efficiency are found an exotic way of determining gained because quantum bits can be an answer to an algorithm—without placed in superpositions of 1 and 0, ever running the algorithm. Using an as opposed to classical bits, which optical-based quantum computer, the are either 1 or 0. Moreover, the logic researchers have presented the first behind the coherent nature of quantum demonstration of “counterfactual information processing often deviates computation,” inferring information from intuitive reasoning, leading to about an answer, even though the some surprising effects. “It seems absolutely bizarre that counterfactual computation—using tauffer information that is counter to what The Kwiat research group at the Alma Mater rian S must have actually happened—could y L. B find an answer without running the not run the search algorithm,” said interrogation schemes, and to my mind, entire quantum computer,” said Kwiat. graduate student Onur Hosten, lead quantum mechanics doesn’t get any hoto b P “But the nature of quantum author of the Nature paper. “We also more mysterious than this.” interrogation makes this amazing showed theoretically how to obtain While the researchers’ optical feat possible.” the answer without ever running the quantum computer cannot be scaled Sometimes called interaction-free algorithm, by using a ‘chained Zeno’ up, using these kinds of interrogation measurement, quantum interrogation effect.” techniques may make it possible to is a technique that makes use of Through clever use of beam splitters reduce errors in quantum computing, wave-particle duality (in this case, of and both constructive and destructive Kwiat said. “Anything you can do to photons) to search a region of space interference, the researchers can put reduce the errors will make it more likely without actually entering that region each photon in a superposition of that eventually you’ll get a large-scale of space. Utilizing two coupled optical taking two paths. Although a photon quantum computer.” interferometers, nested within a can occupy multiple places simul- In addition to Kwiat and Hosten, third, Kwiat’s team succeeded in taneously, it can make an actual co-authors of the Nature paper are Paul Kwiat, right, John Bardeen Professor counterfactually searching a four- appearance at only one location. graduate students Julio Barreiro, of Physics and Electrical and Computer element database using Grover’s Its presence defines its path, and that Nicholas Peters, and Matthew Rakher Engineering, and graduate student quantum search algorithm. can, in a very strange way, negate the (BS ’03, now at the University of Onur Hosten have shown that quantum “By placing our photon in a need for the search algorithm to run. California, Santa Barbara). I computation can determine the answer quantum superposition of running “In a sense, it is the possibility that This work was funded by the Disruptive Technologies to an algorithm—without ever running and not running the search algorithm, the algorithm could run that prevents the algorithm. Office and the National Science Foundation. The we obtained information about the the algorithm from running,” Kwiat conclusions presented are those of the authors and answer even when the photon did said. “That is at the heart of quantum not necessarily of the funding agencies. Of Bits and Bytes: Physics Pioneers Computing at Illinois n 1949, the University received In 1964, the Digital Computer the University of Illinois and beyond. Iapproval to build a copy of a Laboratory—comprised mainly of This issue of Physics Illinois News computer being designed at the Physics faculty—was renamed the features interviews with several of the Institute for Advanced Study in Department of Computer Science, central figures in computing history Princeton, New Jersey. The Illinois but the undergraduate degree program at the U of I, and we invite you to computer group was organized as the in computer science wasn’t introduced enjoy this glimpse of our important Digital Computer Laboratory with until 1972. heritage. I Ralph Meagher, a physicist, named In 1985, the National Science chief engineer for the computer project. Foundation established the Center Completed in 1951 and named for Supercomputing Research and ORDVAC, the computer was one of Development and the National Center the fastest in existence—performing for Supercomputing Applications, with an add time of 92 ms and a Abraham Traub and Ralph Meagher with ILLIAC I making Urbana-Champaign the multiplication time of 700 ms. nation’s only university campus with Measuring 10-ft long, 2-ft wide the University’s radio telescope. two supercomputer centers. Larry and 8.5-ft high, the 5-ton machine Using the ILLIAC for brain power, Smarr, an astrophysicist, was named contained 2,800 vacuum tubes. U of I faculty introduced PLATO, the NCSA’s first director. Its successor, dubbed ILLIAC, was nation’s first computer-based program The NCSA would drive the completed in Fall 1952 and was one of instruction. Beginning in 1959, development of computer visualization of the first electronic computers built Physics faculty member and Control software. Physics graduate student and owned entirely by an educational Systems Laboratory Director Daniel Brand Fortner (BS ’77, MS ’82, PhD institution. Operating initially only Alpert championed the idea of Chalmers ’93), co-founder of Spyglass Inc., 8 hours a day, its schedule was Sherwin (also a Physics faculty member) licensed the software from the gradually expanded to 24-hours-per- that computers could be used for University and developed the first day, six-days-a-week operation. ILLIAC instruction, a concept that was to graphical browser for the Internet, would provide the major portion of the emerge as PLATO. About 25 years later, Mosaic®, in 1995. Physics faculty developed a pattern recognition computer services for the University for Lorella Jones would write the country’s The Department of Physics—its computer, which would become ILLIAC III, to 10 years, finding use in the design of first computerized homework problems faculty and alumni—has had an solve the problem of interpreting millions of other research instruments such as on PLATO for an elementary physics enormous influence on the bubble-chamber photographs. high-energy particle accelerators and course at Illinois. development of computing at 2 PHYSICS ILLINOIS NEWS • 2006 NUMBER 1 Message from the Head his is the seventh issue of Physics only 20 percent of the total university system levels will be a TIllinois News and my last as head UIUC budget comes from state multi-year challenge. I am confident of the department. I will be stepping appropriations, a smaller fraction than that the Department of Physics will down as head and retiring from the comes from tuition. Nevertheless, we come out stronger in the end, but it University this summer. At that time, have been able to hire new faculty, the will need help from all of its friends. I will have completed 39 years as a lifeblood of our department, during I am also confident that the member of the faculty and 6 as head. every year that I have been head. Department will play a major role in As I look back, I am amazed how Between January 2005, when Joe assisting the College of Engineering quickly 39 years has passed and how White took office as the new president and the University of Illinois at much the personnel, research, of the University of Illinois system, Urbana-Champaign to meet their teaching styles, and the outreach and Summer 2006, when my challenges and goals as well. I also programs of the Department of successor takes over, there will have know that the new head of the Physics have changed, and at the been a complete turnover of the Department of Physics will struggle same time how the ethos of administrative hierarchy: Head of with the same issues that Wheeler department—the collegial Urbana Physics, Dean of Engineering, Provost, Loomis and every department head spirit—has endured. The latter is the Chancellor, and President. Starting in since have had to deal with—money most important news I have to Spring 2005, the ground work was and space! report, and I am proud of that. laid for a strategic planning process at It has been a great honor to have During my tenure as head, all levels of the University to redefine served as head of the Department of especially in the last four years, the its mission and its relationship to the Physics, and I am deeply humbled to long-standing implicit covenant State and, at the same time, to expand have been entrusted with that between public universities and its national and international reach. opportunity and responsibility. I their state governments has changed The planning process will come to irreversibly, even at land grant completion in June 2006. universities such as ours. In the Executing the strategic plans at the current academic year, for example, departmental, college, campus, and Jeremiah D. Sullivan First Atom-by-Atom Simulation of a Life Form he computing horsepower of one collaborated with crystallographers at Tof the world’s most powerful the University of California, Irvine— supercomputers has been harnessed Alexander McPherson, a professor of by Swanlund Professor of Physics molecular biology and biochemistry, Klaus Schulten and his research group and research specialist Steven Larson. to visualize the behavior of a complete The group’s results were published in life form, the satellite tobacco mosaic the March issue of Structure (P.L.