Stern-Gerlach Interferometry with the Atom Chip

Abstract

In this invited review in honor of 100 years since the Stern-Gerlach (SG) experiments, we describe a decade of SG interferometry on the atom chip. The SG effect has been a paradigm of quantum mechanics throughout the last century, but there has been surprisingly little evidence that the original scheme, with freely propagating atoms exposed to gradients from macroscopic magnets, is a fully coherent quantum process. Specifically, no full-loop SG interferometer (SGI) has been realized with the scheme as envisioned decades ago. Furthermore, several theoretical studies have explained why it is a formidable challenge. Here we provide a review of our SG experiments over the last decade. We describe several novel configurations such as that giving rise to the first SG spatial interference fringes, and the first full-loop SGI realization. These devices are based on highly accurate magnetic fields, originating from an atom chip, that ensure coherent operation within strict constraints described by previous theoretical analyses. Achieving this high level of control over magnetic gradients is expected to facilitate technological applications such as probing of surfaces and currents, as well as metrology. Fundamental applications include the probing of the foundations of quantum theory, gravity, and the interface of quantum mechanics and gravity. We end with an outlook describing possible future experiments.

A century ago the Stern-Gerlach experiment ruled unequivocally in favor of Quantum Mechanics

“…In the 1990s, a renaissance began in atomic physics, nurtured by the development of techniques to cool and trap atoms [121][122][123]. Based on a combination of molecular beams with laser cooling, these techniques enabled the realization of quantum degeneracy in atomic gases [124][125][126][127][128], optical manipulation of quantum systems [129][130][131], addressing foundational questions [132], examination and quantum simulation of condensed-matter systems [133][134][135][136][137][138][139][140], prototype quantum computers [141,142] and, last but not least, they transformed metrology [143], including the testing of aspects of gravity [96,144].…”

“…Over the past decade, Ron Folman and his group, have demonstrated experimentally that the Stern-Gerlach splitting of a beam of freely propagating atoms subject to macroscopic magnets is a "fully coherent quantum process" [96,97] and implemented a full-loop Stern-Gerlach matter-wave interferometer. A key element of their setup is an atom-chip beam splitter that makes use of a minimum-uncertainty atomic sample derived from a Bose-Einstein condensate of atoms ( 87 Rb) that are stateprepared in an equal superposition of two hyperfine Zeeman states.…”

“…2 of Ref. [96]. In the vertical (1D, longitudinal) arrangement of their experiment, Folman et al let the separated wavepackets freely propagate under gravity and eventually overlap as they spread.…”

“…4 of Ref. [96]. Even in the absence of environmental decoherence, in order to maintain spin coherence at the recombination point, the wavepackets have to be brought together with a spatial, ∆Z, and momentum, ∆P Z , precision such that ∆Z ≪ σ Z and ∆P Z ≪ σ p , where σ Z and σ P are the corresponding uncertainties of .…”

A complete analysis of spin coherence in the full-loop Stern Gerlach interferometer using non-squeezed and squeezed coherent states of the Quantum harmonic oscillator

“…It must be noted that the authors denote the visibility by C in [3]. A key point to observe is that the visibility in the SG interferometer undergoes a Gaussian decay with increasing spatial and momentum splitting between the wave-packets [4]. This result however, suffers from a major drawback, due in part to the fact that it does not account for the temporal evolutions of the spatial and momentum splitting ∆z(t) and ∆p z (t) between the split wave-packets respectively, namely that the consequences arising from Eq.…”