Realization of a complete Stern-Gerlach interferometer

Understand

The Stern-Gerlach (SG) effect, discovered almost a century ago, has become a paradigm of quantum mechanics.

• Surprisingly there is little evidence that the original scheme with freely propagating atoms exposed to gradients from macroscopic magnets is a fully coherent quantum process.
• Specifically, no high-visibility spatial interference pattern has been observed with such a scheme, and furthermore no full-loop SG interferometer has been realized with the scheme as envisioned decades ago.
• On the contrary, numerous theoretical studies explained why it is a near impossible endeavor.