Super-cooled, neutral atoms may replace transistors
08/01/1999
Poul Jessen envisions that super-cooled neutral atoms in a "quantum mechanical computer" will be used when transistor-based binary-computing hits its limit. Jessen, assistant professor of optical sciences at the University of Arizona (UA) in Tucson, says, "In fifty years, quantum information may be the new paradigm for information processing. There are no fundamental laws that says this cannot be done."
Jessen is a former student of William Phillips, who is the recipient of the 1997 Nobel Prize for his work in laser cooling. Now, Jessen heads one of the most active groups in the US, at the UA Optical Sciences Center, studying optical lattices or standing waves of light that trap and control single atoms. This group, in collaboration with colleagues at the University of New Mexico, has begun experiments to test theories that neutral or chargeless atoms, trapped like individual eggs in an egg carton by a lattice created by interfering laser beams and super-cooled to the point of zero motion, will work for quantum computing.
The group has succeeded in cooling light-trapped atoms to the zero point of motion, a crucial pure vibrational state and the logical zero for a quantum mechanical computer. "Cooling atoms is no small achievement," says Jessen. "These atoms are colder than liquid helium by roughly the same factor that liquid helium is colder than the center of the sun."
Jessen's scheme involves stacking atom-filled optical lattices so neutral atoms will sufficiently interact to make logic operations possible. "If the scheme works, the big advantage is that atoms can be easily accessible for laser manipulation, but remain isolated from the surrounding environment. Random outside forces that act on tiny quantum bits is perhaps the greatest problem to confront when trying to build a real quantum computer," Jessen says.
"A quantum computer, very loosely speaking, would allow you to enter all possible inputs at one time and perform all the corresponding computations in parallel," notes Jessen. "However, this is a very simplistic way of putting it. The laws of quantum physics only allow you to observe one of the many possible outputs each time you run the computer, so you have to be very clever about how you look at the results."
Researchers have discovered that several classes of computational problems can be solved in ways that take advantage of quantum parallelism. How powerful is it? A quantum computer would simultaneously carry out a number of computations equal to two to the power of the number of input bits. In other words, if you were to feed a modest 100 bits of information into such a computer, the machine would process in parallel 2100 different inputs simultaneously. The higher the number of bits fed into such a computer, the exponentially greater advantage a quantum mechanical computer has over a classical computer.
Jessen confesses, "It's important to be honest and say that physicists and computational scientists are far from done with the study of quantum information. It's not yet known what kinds of problems such computers might do better than a classical computer."