Quantum theory is one of the two revolutions in modern day physics. However, its underlying root is still very much a mystery. Here we revisit the Stern-Gerlach Experiment, a paradigm of quantum theory, and by using modern technology have managed to shed new light on this fundamental spin quantization experiment. Most notably, we have shown that the Stern-Gerlach splitting of a single object so that it occupies two locations simultaneously (a superposition state), is a real and coherent process.

Nobel laureate Richard Feynman noted that “nobody really understands quantum mechanics”. Indeed, 100 years after its conception it is vital to re-examine its most basic premises. On a fundamental level this will eventually enable to form a more accurate extension to quantum mechanics, and on a practical level, it will help advance the new era of quantum technology. In the 100 years since the Stern-Gerlach Experiment, there was an enormous debate on whether the splitting they saw was actually quantum (i.e. coherent). Numerous theoretical papers voted against. Heroic experiments have tried to give an answer. But only now, with the new technology of the atom chip, we were able to give a clear answer. More so, we have shown that the Stern-Gerlach effect may be used to test Quantum Mechanics in new regimes (superposition of large masses), and furthermore to probe one of the most important open questions in physics, namely, the interface between the two revolutions of modern physics, Quantum Mechanics and General relativity (gravity).

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