Tucker's theory employed by Herschel and ALMA telescopes

Ever wonder how stars, galaxies, or even the universe were formed? Within the next few years, you may no longer have to speculate. By 2012, astonishing advances in astronomy will be achieved due to the recent development of two powerful telescopes.

While the Herschel Space Observatory will orbit far from earth, the Atacama Large Millimetre Array (ALMA) will be built on the top of the Chilean Andes. Both telescopes employ superconductor-insulator-superconductor (SIS) receivers based on a theory that ECE Professor John R Tucker developed from 1974 to 1980. All (sub) millimeter-wave receivers on telescopes are designed with the ‘Tucker theory,’ and the ultimate limit of physics is approached in sensing signals due to its unanticipated prediction of noiseless amplification.

"People would like to know how the universe has evolved, and there is a lot to be learned," Tucker said. "When you have the ultimate receivers, then you have the ultimate tool to open up a big part of the early universe."

The Herschel Space Observatory is expected to reveal new information about the earliest, most distant stars and galaxies, as well as those closer to home in space and time. The device, which will be a large part of the European Space Agency’s Horizon 2000 program, is scheduled to launch later this year, and return in 2011 or 2012. The United States and nine other countries have contributed to its overall design and completion.

The pre-launch testing for Herschel was ongoing during the 19^th International Symposium on Space Terahertz Technology conference (ISSTT), April 27 through April 30, in Groningen - the home of the Netherlands Space Agency (SRON). At the conference banquet, Tucker gave a presentation on early work leading up to the SIS receivers on Tuesday, April 29. People from all of the organizations involved in Herschel, ALMA, and a dozen smaller projects attended from around the world.

The Atacama Large Millimeter Array (ALMA) will consist of 64 moveable 12 meter antennas with more than 1,000 SIS receivers working together as a giant telescope. The 16,500 foot site in Chile was selected to utilize their quantum sensitivity. Funded by approximately $1.3 billion from an international partnership between North America and Europe, research and development of ALMA began in June 1998. Final construction is scheduled to take place in 2012. According to the National Research Council of Canada’s Web site, the ALMA will "hold the key to understanding such processes as planet and star formation, the formation of early galaxies and galaxy clusters, and the formation of organic and other molecules in space." Tucker said the origins of life may also be connected to this work.

"They are both huge projects, and it’s really fantastic," Tucker said. "There’s just been so much technology put into this; and these are two of the biggest projects in astronomy."

Tucker earned his bachelor’s degree in physics from the California Institute of Technology in 1966 and his PhD from Harvard University in 1971. During his last year at Harvard, he served as a resident visitor and consultant in the theoretical physics group at Bell Telephone Laboratories. He completed his postdoctoral research with Leo Kadanoff at Brown University.

In 1973, Tucker became a technical staff member of the Electronics Research Laboratory at the Aerospace Corporation in Los Angeles, California. He arrived just as his co-workers had developed their super-Schottky diode detector based on tunneling from a semiconductor to a superconductor.

"They kept lowering the temperature, and it got more and more nonlinear," Tucker said. "The people who were doing this asked me, ‘Is there any limit to its sensitivity?’ In a minute or two, photon-assisted tunneling came to mind."

While the effect was known in SIS junctions about 10 years prior to their research, no one had developed it. Tucker created a theory that showed how to reach the ultimate limit in sensing millimeter wave signals based on photon-assisted tunneling. The full quantum mixer theory was published in 1979.

In 1980, Tucker predicted noiseless amplification of incoming signals in a heterodyne SIS mixer. This gain effect was confirmed at University of California, Berkeley, in a few weeks. By reducing (instead of amplifying) the noise from the output amplifier, the quantum limit could be closely approached in SIS receivers.

That year, groups at University of California, Berkeley, the California Institute of Technology, the NASA Goddard Institute in New York, and Chalmers University in Sweden began developing SIS receivers for use in astronomy.

"Immediately, they were more successful than all of the other receivers there had been before," Tucker said.

In 1981, John Bardeen brought Tucker to the University of Illinois to work with him on current transport in charge-density-wave materials. Bardeen's idea that tunneling was involved in CDWs did not prove out, and Tucker went on to explore silicon-based electronics at the atomic level.