Realization of a complete Stern-Gerlach interferometer: Toward a test of quantum gravity.

Yair Margalit,Carsten Henkel,Samuel Moukouri,Yonathan Japha,Zhifan Zhou,Omer Amit,Daniel Rohrlich,Sougato Bose,Or Dobkowski,Anupam Mazumdar,Ron Folman

doi:10.1126/sciadv.abg2879

Abstract

The Stern-Gerlach effect, found a century ago, has become a paradigm of quantum mechanics. Unexpectedly, until recently, there has been little evidence that the original scheme with freely propagating atoms exposed to gradients from macroscopic magnets is a fully coherent quantum process. Several theoretical studies have explained why a Stern-Gerlach interferometer is a formidable challenge. Here, we provide a detailed account of the realization of a full-loop Stern-Gerlach interferometer for single atoms and use the acquired understanding to show how this setup may be used to realize an interferometer for macroscopic objects doped with a single spin. Such a realization would open the door to a new era of fundamental probes, including the realization of previously inaccessible tests at the interface of quantum mechanics and gravity.

Highlights

The discovery of the Stern-Gerlach (SG) effect [1, 2] was followed by ideas concerning a full-loop SG interferometer (SGI) consisting of a beam of atoms exposed to field gradients from macroscopic magnets [3]
As we extend the delay time Td1, the wave packets start to split in space and we observe a decay in visibility that cannot be restored using T2 alone, as the distance between the wave packets becomes larger than their coherence length lz
While some proposals exist with the goal of probing gravity with atoms [20, 21, 47, 48], here, we aim at using a superposition of a macroscopic object

Summary

Introduction

The discovery of the Stern-Gerlach (SG) effect [1, 2] was followed by ideas concerning a full-loop SG interferometer (SGI) consisting of a beam of atoms exposed to field gradients from macroscopic magnets [3]. Schwinger, and Scully [6,7,8,9] analyzed the problem in more detail and coined it the Humpty-Dumpty (HD) effect. They too concluded that for substantial coherence to be observed, exceptional accuracy in controlling magnetic fields would be required. While atom interferometers based on light beam splitters enjoy the quantum accuracy of the photon momentum transfer [10], the SGI magnets have no such quantum discreteness and suffer from inherent lack of flatness due to Maxwell’s equations. Claims have even been made that no coherent splitting is possible at all [12]

Methods

Results

Conclusion