Abstract
Stern-Gerlach and/or matter-wave interferometry has garnered significant interest amongst members of the scientific community over the past few decades. Early theoretical results by Schwinger et al. demonstrate the fantastic precision capabilities required to realize a full-loop Stern-Gerlach interferometer, i.e., a Stern-Gerlach setup that houses the capability of recombining the split wave-packets in both, position and momentum space over a certain characteristic interferometric time. Over the years, several proposals have been put forward that seek to use Stern-Gerlach and/or matter-wave interferometry as a tool for a myriad of applications of general interest, some of which include tests for fundamental physics (viz., quantum wave-function collapse, stringent tests for the Einstein equivalence principle at the quantum scale, breaking the Standard Quantum Limit (SQL) barrier, and so forth), precision sensing, quantum metrology, gravitational wave detection and inertial navigation. In addition, a large volume of work in the existing literature has been dedicated to the possibility of using matter-wave interferometry for tests of quantum gravity. Inspired by the developments in this timely research field, this Perspective attempts to provide a general overview of the theory involved, the challenges that are yet to be addressed and a brief outlook on what lays ahead.
Highlights
Stern-Gerlach interferometry is considered to be by some, an ideal candidate for possibly testing theories of quantum gravity in simple table-top experiments
Significant progress has been made in the area of optomechanical cavity cooling in recent years, making such sensitive experiments feasible [67,68,69]
The idea that Stern-Gerlach and/or matterwave interferometry could be used as a tool for the detection of gravitational waves has seen much development over the recent years
Summary
Stern-Gerlach interferometry is considered to be by some, an ideal candidate for possibly testing theories of quantum gravity in simple table-top experiments. Consider the proposal put forward by Bose et al (see [5]), that suggests the use of two mesoscopic test masses initially trapped in two spatiallyseparated harmonic potential wells that are later released into two spatially-separated Stern-Gerlach interferometers, one corresponding to each harmonic trap These masses each contain an embedded spin-1/2 (see [4]) that undergo spatial and momentum splitting once after entering the SG interferometers (i.e., in the presence of an applied magnetic field gradient). The scheme proposed in [5] (using two adjacently-placed SG interferometric setups) entails the following steps: we take two test masses containing embedded spin-1/2 particles and split them spatially by exploiting the Stern-Gerlach effect (through the application of magnetic field gradients in the adjacently-placed SG interferometric setups). The scheme proposed in [5] in essence attempts to realize the idea that if two quantum systems (in our case, we have test masses whose spatial degrees of freedom exist in a quantum superposition) get entangled through the interaction with a third mediator (in our case, this is the gravitational field) [15], the third mediator must be quantum in nature, for which the authors in [15] provide an explicit information theoretic proof
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