An optical analogue to Schrödinger’s cat

Erwin Schrödinger’s cat gedanken experiment of 1935 presented the possibility of entanglement between microscopic and macroscopic physical systems and the resulting quantum behavior of macroscopic objects. In the years since, researchers have realized analogous systems with entanglement between microscopic and macroscopic structures—for example, the entanglement between a trapped ion and the vibrational state in the trap described in David Wineland’s Nobel Prize–winning work. However, the resulting macroscopic quantum superposition states typically had limited utility because their creation had a low probability or they had short transmission distances. Now Gerhard Rempe of the Max Planck Institute of Quantum Optics in Germany and his colleagues have deterministically produced a macroscopic light pulse with a controlled superposition state.