I make reference to this often in various discussion groups, so I thought I should have it here in one place so that it is handy.
These are the papers that clearly show the Schrodinger Cat-type states (alive+dead, and not alive or dead). All the relevant details are there and anyone interested should read them. Also included is the reference to a couple of review articles which are easier to read, and the reference to two Leggett's papers, who was responsible in suggesting this type of experiments using SQUIDs in the first place. Again, the papers have a wealth of citations and references.
The two experiments from Delft and Stony Brook using SQUIDs are:
C.H. van der Wal et al., Science v.290, p.773 (2000).
J.R. Friedman et al., Nature v.406, p.43 (2000).[ArXiv version can be found here]
Don't miss out the two review articles on these:
G. Blatter, Nature v.406, p.25 (2000).
J. Clarke, Science v.299, p.1850 (2003).
However, what I think is more relevant is the paper by Leggett (who, by the way, started it all by proposing the SQUIDs experiment in the first place):
A.J. Leggett "Testing the limits of quantum mechanics: motivation, state of play, prospects", J. Phys. Condens. Matt., v.14, p.415 (2002).
A.J. Leggett "The Quantum Measurement Problem", Science v.307, p.871 (2005).
This paper clearly outlines the so-called "measurement problem" with regards to the Schrodinger Cat-type measurements.
I may add more to this post if more new experiements/reviews are reported, so this entry may grow over time.