Schroedinger's cat experiment has been performed in the lab, although the part of the cat was played by a relatively large atom. In this case, the experiment was conducted using a principle called entanglement. This is where two atomic structures become so entwined that they become effectively identical, regardless of how far apart they are placed. For example, two entanged neutrons could be placed as far apart as you like, but when one is measured and it collapses to a single state, rather than a superposition one, it's "twin" will also collapse to a single position instantly.

Strangely, entanglement appears to defy the light speed barrier rule. It doesn't appear to matter how far apart the particles are placed, they react to each other instantly. For more information, see the EPR Paradox experiment, or search for Bell-Aspect experiments, which describe how information cannot be transmitted faster than light speed.

Many quantum theorists have speculated that this is evidence of parallel universes. One particle is in our universe and it's twin is in the closest parallel¹ universe. One big question is, if we can see a particle from another universe, why can't we see a person or a table? The answer is that they are there, but are rotated at 90^o to our "reality." This is a metaphor, a lie to children to explain something difficult to describe. Imagine that our universe (3 space dimentions + 1 time dimension + possible others) was a flat sheet. The nearest universe is not another sheet lying on top, but rather a sheet that intersects ours at a 90^o angle. The next universe intersects that universe again, and so on, so that no two univserse are lying on top of each other. For more information, look up Brane (or M-Brane²) theory.

Experiments have placed "massive" objects into superposition, buckyballs, commonly known as Carbon 60. These are tiny compared to you or I, but are a spherical cage built of 60 carbon atoms. In 1999, Anton Zeilinger at the University of Vienna showed that a buckyball could travel through two parallel slits at the same time (see Young's Slits experiment above). This is quite a break through, and again, like Schrodinger, the boundaries of superposition have become "blurry." A further experiment is planned, which will use a nanotube, much larger than a buckyball, but still tiny, like an atomic sized hair strand. It will involve magnetic attraction to bend to tube towards the magnet, yet should also stay unbent, thereby being in a superposition state. Unfortunately this experiment must be performed in space, gravity and vibrations would overwhelm the experiment's sensitivity.

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¹ The term derives from alternate time line, such as a timeline when Hitler defeated the Allies, the time line would run parallel to ours if drawn on a blackboard. See Back To The Future Part II for more information.
² It's sort of a physicists joke.^3
3 Say it out loud. Brane is prounounced the same as brain.