Biography of Karl Hess BIOGRAPHY

hysicists have strived for centu- back,’’ Hess said. His persistence paid ries to understand the behavior off; in 1977, the University of Illinois of , information crucial offered him a visiting associate profes- P for explaining electricity and the sorship. physical properties of all materials. Al- though electrons are exponentially too Supercomputers, Super small to see, researchers have developed After Hess returned to Illinois, he a variety of techniques for simulating worked to improve the efficiency of electronic nature and movement with charge-coupled devices, computer models. A leader in this field chips that record images in video cam- is Karl Hess, professor of electrical and eras. However, craving more basic study, computer engineering at the University he soon teamed up with engineering of Illinois, Urbana. professor Ben Streetman, now at the With his colleagues, Hess has devel- University of Texas at Austin, to investi- oped numerous tools for dis- gate a broader class of semiconductor cerning the behavior of electrons in materials and devices. The two scientists solids, semiconductor lasers, and other developed the concept of ‘‘real space devices. His work has earned him many Karl Hess. transfer’’ (4), which explains the perfor- grants and accolades, including the rare mance of certain high-frequency transis- dual election to both the National Acad- fessor at the University of Vienna. A tors. Streetman also mentored Hess on emy of Engineering (2001) and the Na- the politics of American university life. tional Academy of Sciences (2003). In year later, he met University of Illinois professor , who was on a His advice helped Hess land a tenured his Inaugural Article (1), published in professorship of electrical and computer lecture tour throughout Europe. A giant MATHEMATICS this issue of PNAS, Hess and mathema- engineering at the University of Illinois tician Walter Philipp discuss certain lim- of electrical engineering, Bardeen coin- vented the transistor in 1947 and was a in 1980, a position he still holds. itations of Bell’s Theorem, a current At about that time, Hess’ expertise cornerstone for quantum theory. The pioneer in the field of superconductiv- ity: the complete disappearance of elec- in semiconductor research caught the authors’ conclusions suggest completely attention of the United States Naval new interpretations of quantum mechan- trical resistance in some substances, especially at very low temperatures. Research Laboratory (NRL), which ics and may help foster the development assigned him confidential military re- of quantum computers. When Bardeen offered Hess a favor in return for some translating work, Hess search. His work with NRL, as well as Combining Science and Technology asked for help finding a postdoctoral his consequent research for the Office of Naval Research and the Army Re- As a young boy in Vienna, , Hess fellowship in the United States. Bardeen didn’t let Hess down. After search Office, was invaluable in shaping became fascinated with electricity. Dur- his future research interests. Although ing his elementary years, he came across receiving a Fulbright scholarship in 1973, Hess left Vienna with his wife and unable to elaborate on the specifics, a book on 19th century inventions in his Hess said, ‘‘It gave me an overview of father’s library. ‘‘I read the book in- two children to join Bardeen at the University of Illinois. Hess soon met what was going on in semiconductor tently, especially the section on electric- research in the United States.’’ ity,’’ he said. Hess continually tinkered Chih-Tang Sah, who was also at the University of Illinois and is coinventor In his nonclassified research, Hess with small electrical devices, building his sought a way to determine electrical first microphone at age 8. of a technology known as compli- mentary metal oxide semiconductor properties, such as conduction, resis- A particularly engaging high school tance, and radar or microwave absorp- teacher encouraged Hess to focus on a (CMOS), now ubiquitous in chip tech- nology. For the next 2 years, Hess and tion, in solids or career in applied physics. With this ad- through computer simulation. Toward vice in mind, Hess studied physics and Sah combined their expertise to solve the Boltzmann transport equation, which this end, he and his graduate students mathematics at the University of Vi- developed the full-band Monte Carlo enna. He continued his education at the describes electronic transport in transis- tors (3). ‘‘I was a little intimidated be- method, a combination of the Boltz- same university, pursuing a doctorate in mann equation and applied physics under the mentorship of cause I was surrounded by these famous (5). Quantum theory dictates that elec- solid-state physicist Karlheinz Seeger. people, Bardeen and Sah,’’ said Hess. trons are both a particle and a wave; For his thesis, Hess investigated elec- ‘‘But at the same time, I was also enor- however, previous attempts to predict tronic transport in semiconductors, crys- mously excited because this was the the path of electrons through a solid talline materials with conductivity place where they did what I liked most, neglected the particle’s wave-like nature, between that of a metal and an insula- combining science and technology.’’ yielding imprecise results. Hess and his tor. The work was partly experimental In 1974, Hess moved back to Vienna students used supercomputers to include and partly theoretical: by irradiating with his family. For the next 3 years, he electrons’ wave structures into their cal- semiconductors with microwaves, thus worked as an assistant professor and culations, creating simulation methods exciting electrons, Hess developed theo- lecturer at the University of Vienna. ries on how the electrons interacted However, he strove to retain connec- with each other and with the semicon- tions to Illinois, communicating often This is a Biography of a recently elected member of the ductor’s lattice structure (2). with Bardeen and Sah. ‘‘My wife, Sylvia, National Academy of Sciences to accompany the member’s After earning his doctoral degree in liked it there, and so did my children, Inaugural Article on page 1799. 1970, Hess worked as an assistant pro- Ursula and Karl. We wanted to move © 2004 by The National Academy of Sciences of the USA

www.pnas.org͞cgi͞doi͞10.1073͞pnas.0400379101 PNAS ͉ February 17, 2004 ͉ vol. 101 ͉ no. 7 ͉ 1797–1798 Downloaded by guest on October 2, 2021 that provided accurate predictions for as MINILASE (6, 7). The program accu- To construct a quantum computer, electronic transport in semiconductors. rately simulates quantum well laser researchers must first understand the Now a popular simulation technique design adjustments and cuts down basis of quantum information, a topic used throughout electrical engineering, calculation time. closely related to the work of British the full-band Monte Carlo method physicist John Bell. Bell’s famous 1964 forms the base of several commercial Bell’s Theorem, Revised Theorem (11), which sprang from a de- software packages, such as IBM’s bate between and Niels Hess credits the evolution of his current Bohr, appears to show that an event in DAMOCLES and Integrated Systems research interests to the influence of his one location could instantaneously af- Engineering’s DESSIS programs. work environment at the Beckman Insti- fect a second, nonlocal event, a phe- A chance opportunity prompted Hess tute for Advanced Science and Technol- nomenon sometimes referred to as to focus his engineering and computer ogy at the University of Illinois. In 1984, ‘‘spooky .’’ In his simulation skills on optoelectronics, a philanthropists Arnold and Mabel Beck- Inaugural Article, found on page 1799, branch of electronics that deals with man offered the University of Illinois a Hess and mathematician Walter Philipp devices for emitting, modulating, trans- generous grant to build an interdiscipli- argue that Bell’s Theorem breaks down given certain parameters. This finding mitting, and sensing light. When Hess’s nary science center to combine physical University of Illinois colleague Nick Ho- could influence current understanding and biological research interests. Hess lonyak, Jr., was unable to attend a 1984 of the flow of quantum information and chaired one of two faculty committees meeting of high-level scientists inter- might even lead to new interpretations at Illinois that wrote a proposal for this ested in optics technologies, Hess went of quantum mechanics. Hess acknowl- center, and, in 1989, the Beckman Insti- in his place. ‘‘I got the feeling [at the edges that this conclusion has already stirred a heated debate throughout the meeting] that the field of optoelectron- tute opened its doors with Hess serving as associate director. Since then, Hess’s field of quantum physics; however, he is ics was in need of computer-aided de- confident in his work and plans to build sign and simulation tools,’’ he said. Over close involvement with life scientists has stimulated an interest in nanostructures on these findings in future research. the next several years, Hess and his stu- ‘‘I’ve worked on this [Bell’s Theorem and biomolecules. He has published sev- dents developed a program to simulate research] more than anything else. For quantum well laser diodes, tiny lasers eral papers reflecting this new curiosity the last 4 years, I dream of it, I go to found in bar-code scanners, CD players, over the last decade (8–10). However, bed with it, and I wake up with it. It’s and fiber-optic technology. Previous re- rather than pursue applications of nano- close to driving me crazy, but I think search had supplied a basic design for structures in the biological sciences, I’ve come now to a conclusion about it,’’ these lasers. However, engineers were Hess became interested in applying he said. ‘‘It might be my greatest contri- faced with hours of laborious calcula- nanoscience to quantum computing. bution to science.’’ tions to predict the effects of new design Currently only a theoretical concept, Special thanks are extended to David Ferry, modifications, which frequently led to quantum computation is based on the Regents’ Professor of Electrical Engineering inaccurate results. To improve the accu- simultaneous interaction of its compo- at Arizona State University, for help in re- racy and speed of these calculations, nent devices, in contrast to standard searching this biography. Hess’s team created a new algorithm computing machines that work their de- and incorporated it into software known vices in sequence. Christen Brownlee, Science Writer

1. Hess, K. & Philipp, W. (2004) Proc. Natl. Acad. 5. Shichijo, H. & Hess, K. (1981) Phys. Rev. B 23, 9. Hess, K., Register, L. F., Tuttle, B., Lyding, J. & Sci. USA 101, 1799–1805. 4197–4207. Kizilyalli, I. (1998) Phys. E Low-Dimens. Syst. 2. Hess, K. & Seeger, K. (1968) Z. Phys. 218, 431– 6. Grupen, M. & Hess, K. (1998) IEEE J. Quantum Nanostruct. 3, 1–7. 436. . 34, 120–140. 10. Hess, K. (2003) in Nanoscience, Engineering, and 3. Hess, K. & Sah, C. T. (1974) Phys. Rev. B 10, 7. Klein, B., Register, L. F., Grupen, M. & Hess, K. Technology, eds. Goddard, W., III, Brenner, D., 3375–3386. (1998) Opt. Express 2, 163–168. Lyshevski, S. & Iafrate, G. (CRC, Boca Raton, 4. Hess, K., Morkoc, H., Shichijo, H. & Streetman, 8. Macucci, M., Hess, K. & Iafrate, G. J. (1997) Phys. FL), pp. 2-1–2-7. B. G. (1979) Appl. Phys. Lett. 35, 469–471. Rev. B 55, 4879–4882. 11. Bell, J. S. (1964) Physics 1, 195–200.

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