Gravitational Aharonov-Bohm effect

{{Main article|Aharonov–Bohm effect}}

{{Main article|Aharonov–Bohm effect}}

There are many variants of the Aharonov-Bohm effect in electromagnetism. Here we review an electric version of the Aharonov-Bohm effect that is most similar to the gravitational effect which has been experimentally observed. This electric effect is caused by a charged particle (say, an electron) being in a superposition of traveling down two different paths. In both paths, the [[electric field]] that the electron sees is zero everywhere along the path, but the scalar [[electric potential]] that the electron sees is not the same for both paths.

There are many variants of the Aharonov-Bohm effect in electromagnetism. Here we review an electric version of the Aharonov-Bohm effect that is most similar to the gravitational effect which has been experimentally observed. This electric effect is caused by a [[charged particle]] (say, an electron) being in a superposition of traveling down two different paths. In both paths, the [[electric field]] that the electron sees is zero everywhere along the path, but the scalar [[electric potential]] that the electron sees is not the same for both paths.

[[File:ElectricAB.png|frameless|upright=3.0]]

[[File:ElectricAB.png|frameless|upright=3.0]]

== Gravitational effect ==

== Gravitational effect ==

Just as there are many variants of the Aharonov-Bohm effect in electromagnetism, there are many variants of the gravitational effect. The simplest version of the gravitational effect is analogous to the electric effect above, with the electron replaced by a small test mass such as an atom, and the 2 charges that create an electric potential replaced by 2 masses that create a gravitational potential.

Just as there are many variants of the Aharonov-Bohm effect in electromagnetism, there are many variants of the gravitational effect. The simplest version of the gravitational effect is analogous to the electric effect above, with the electron replaced by a small test mass such as an atom, and the 2 charges that create an electric potential replaced by 2 masses that create a [[gravitational potential]].

[[File:GravAB.png|frameless|upright=3.0]]

[[File:GravAB.png|frameless|upright=3.0]]

In January 2022, a team led by Mark Kasevich announced that they had experimentally observed a gravitational Aharonov-Bohm effect with an experiment broadly similar to the one outlined above.{{Cite journal |last=Overstreet |first=Chris |last2=Asenbaum |first2=Peter |last3=Curti |first3=Joseph |last4=Kim |first4=Minjeong |last5=Kasevich |first5=Mark A. |date=2022-01-14 |title=Observation of a gravitational Aharonov-Bohm effect |url=https://www.science.org/doi/10.1126/science.abl7152 |journal=Science |language=en |volume=375 |issue=6577 |pages=226–229 |doi=10.1126/science.abl7152 |issn=0036-8075|url-access=subscription }}

In January 2022, a team led by Mark Kasevich announced that they had experimentally observed a gravitational Aharonov-Bohm effect with an experiment broadly similar to the one outlined above.{{Cite journal |last=Overstreet |first=Chris |last2=Asenbaum |first2=Peter |last3=Curti |first3=Joseph |last4=Kim |first4=Minjeong |last5=Kasevich |first5=Mark A. |date=2022-01-14 |title=Observation of a gravitational Aharonov-Bohm effect |url=https://www.science.org/doi/10.1126/science.abl7152 |journal=Science |language=en |volume=375 |issue=6577 |pages=226–229 |doi=10.1126/science.abl7152 |issn=0036-8075|url-access=subscription }}

The source of the gravitational potential in their experiment was a single 1.25 kg tungsten mass. The test masses were [[rubidium]]-87 atoms. The tungsten mass was fixed, so the gravitational field caused by the tungsten mass was not zero everywhere along the paths of the ⁸⁷Rb atoms. This means that the phase shift of the rubidium atoms between the 2 paths was not caused by a gravitational potential energy difference alone, but also by a difference in the gravitational force felt by the atoms in the 2 paths. By detecting a difference in the phase shift between when the tungsten mass is present and when it is not present, they observed a phase shift consistent with that predicted by the Aharonov-Bohm effect.

The source of the gravitational potential in their experiment was a single 1.25 kg tungsten mass. The test masses were [[rubidium]]-87 atoms. The tungsten mass was fixed, so the gravitational field caused by the tungsten mass was not zero everywhere along the paths of the ⁸⁷Rb atoms. This means that the phase shift of the rubidium atoms between the 2 paths was not caused by a gravitational [[potential energy]] difference alone, but also by a difference in the gravitational force felt by the atoms in the 2 paths. By detecting a difference in the phase shift between when the tungsten mass is present and when it is not present, they observed a phase shift consistent with that predicted by the Aharonov-Bohm effect.

The "beamsplitters" and "mirrors" used to make the ⁸⁷Rb atoms interfere are not solid-state components as would be the case with standard interferometers with light. Rather, they consisted of laser pulses that coherently transfer momentum between the atoms and photons.{{cite journal |last1=Cronin |first1=Alexander D. |last2=Schmiedmayer |first2=Jörg |last3=Pritchard |first3=David E. |title=Optics and interferometry with atoms and molecules |journal=Reviews of Modern Physics |date=28 July 2009 |volume=81 |issue=3 |pages=1051–1129 |doi=10.1103/RevModPhys.81.1051|hdl=1721.1/52372 |hdl-access=free |arxiv=0712.3703 }}

The "beamsplitters" and "mirrors" used to make the ⁸⁷Rb atoms interfere are not solid-state components as would be the case with standard interferometers with light. Rather, they consisted of laser pulses that coherently transfer momentum between the atoms and photons.{{cite journal |last1=Cronin |first1=Alexander D. |last2=Schmiedmayer |first2=Jörg |last3=Pritchard |first3=David E. |title=Optics and interferometry with atoms and molecules |journal=Reviews of Modern Physics |date=28 July 2009 |volume=81 |issue=3 |pages=1051–1129 |doi=10.1103/RevModPhys.81.1051|hdl=1721.1/52372 |hdl-access=free |arxiv=0712.3703 }}