Quantum Uncertainty Limit for Stern-Gerlach Interferometry with Massive Objects.

We analyze the fundamental coherence limit of a nano-object with an embedded spin in a Stern-Gerlach interferometer. This limit stems from the which-path information provided by the object's rotational degrees of freedom due to the evolution of their quantum uncertainty. We show that such interferometry is straightforward in a weak magnetic field and short duration. Large wave packet separation is made possible with proper fine-tuning over long durations. This opens the door to fundamental tests of quantum theory and quantum gravity. The results and conclusions are extendable to any type of interferometry with complex objects.