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. Previously, we have presented the first spatial SG interference pattern [1]. Here we demonstrate for the first time both a high-visibility spatial SG interference pattern and a full-loop SG interferometer, based on an accurate magnetic field, originating from an atom chip, that ensures coherent operation within strict constraints described by previous theoretical analyses [2]. Achieving this high level of control over magnetic gradients may facilitate technological applications such as large-momentum-transfer beam splitting for metrology with atom interferometry, ultra-sensitive probing of electron transport down to shot noise and squeezed currents, as well as nuclear magnetic resonance and compact accelerators. Recently the SG interferometer allowed us to put a clock in a spatial superposition [3,4], and to realize a universal quantum work meter [5].

[1] Shimon Machluf, Yonathan Japha & Ron Folman, Coherent Stern–Gerlach momentum splitting on an atom chip, Nat. Commun. 4:2424 (2013).

[2] Yair Margalit, Zhifan Zhou, Or Dobkowski, Yonathan Japha, Daniel Rohrlich, Samuel Moukouri & Ron Folman, Realization of a complete Stern-Gerlach interferometer, arXiv:1801.02708 (2018).

[3] Yair Margalit, Zhifan Zhou, Shimon Machluf, Daniel Rohrlich, Yonathan Japha & Ron Folman, A self-interfering clock as a “which path” wit- ness, Science 349, 1205 (2015).

[4] Zhifan Zhou,Yair Margalit, Daniel Rohrlich, Yonathan Japha & Ron Folman, Quantum complementarity of clocks in the context of general relativity, Class. Quantum Grav. 35, 185003 (2018).

[5] Federico Cerisola, Yair Margalit, Shimon Machluf, Augusto J. Roncaglia, Juan Pablo Paz & Ron Folman, Using a quantum work meter to test non-equilibrium fluctuation theorems, Nat. Commun. 8:1241 (2017).