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Quantum phenomena are usually only observable on microscopic scales. A typical macroscopic object is so strongly coupled to its environment that it rapidly decoheres into a classically well-defined state. In the early 1980, Leggett and collaborators proposed that under suitable conditions, some macroscopic systems, most notably superconductors, could be sufficiently well isolated from their environment to be put into a superposition of macroscopically distinct states, a la Schroedinger's cat. I will present recent experimental evidence* that a SQUID (Superconducting QUantum Interference Device) can be put into a superposition of magnetic-flux states that differ by ~1 microampere in current and ~1010 Bohr magnetons in magnetic moment. Using pulsed microwaves, we psuedo-spectroscopically measure the energy levels of the SQUID and find a level anticrossing at the point where the two flux states would classically become degenerate. At the anticrossing the eigenstates of the SQUID have become the symmetric and antisymmetric superpositions of the macroscopically distinct flux states. I will discuss current efforts to observe the quantum coherent oscillations of the SQUID's flux between these two states.
* J. R. Friedman et al., Nature, 406 , 43 (2000).