Schrödinger's SQUID; October 2000; Scientific American Magazine; by Graham P. Collins; 2 Page(s)

Schrodinger's cat turned 65 this year, but instead of thinking about retirement, the quantum feline is making increasingly bolder appearances. Recently two independent groups have demonstrated the largest examples of Schrodinger's cat states by using superconducting loops. In the original thought experiment, quantum effects and a Rube Goldberg-like poison apparatus rendered the cat simultaneously alive and dead inside its sealed torture chamber. In the new experiments, an electric current stood in for the cat and flowed both ways around a loop at the same time. Tony Leggett of the University of Illinois at Urbana-Champaign, one who suggested in the 1980s that such large quantum mechanical systems could be demonstrated, calls the research "a milestone in experimental quantum physics."

The key phenomenon at work is superposition of waves-similar to the way different individual sound waves from people chatting at a party overlap and add up to a total sound wave that goes into our ears. In quantum mechanics, matter itself behaves like a wave: electrons and other particles can exist in superpositions of different states.