Schrödinger's cat
In 1935 Schrödinger proposed a thought experiment in which a cat inside a box could be both dead and alive at the same time. In 1996 researchers at NIST in the US created a "Schrödinger cat" state in which a beryllium ion could be in two places at once. The NIST team started with an ion in a quantum superposition of two internal electronic states. Lasers then coupled these internal states to vibrational states in the trap: the wave packet associated with one internal state started moving to the left, while the other started moving to right. At their widest separation the wave packets, which measure 7 nm across, were 80 nm apart. The ion itself is only about 0.1 nm across (C Monroe et al. 1996 Science 272 1131).