Synopsis: Skydiving Spins

Atom interferometry shows that the free-fall acceleration of rubidium atoms of opposite spin orientation is the same to within 1 part in 10 million.

It’s textbook physics: Let go of two objects of different mass in the absence of friction forces, and the objects fall at the same rate. This concept, known as universality of free fall, has been verified in a variety of methods and systems. Zhong-Kun Hu, from Huazhong University of Science and Technology in China, and co-workers have tested the principle with rubidium atoms of opposite spin orientation. They found that spin orientation doesn’t matter—the atoms still fall at the same rate.

Testing the universality of free fall isn’t just a fun exercise. Almost all quantum theories of gravity, which attempt to describe gravity using quantum mechanics, predict the violation of the principle, with free-fall acceleration depending on a quantum particle’s properties, such as its spin. Studies with quantum particles could provide a means to constrain these theories.

Hu and colleagues used atom interferometry to measure the free-fall acceleration of rubidium-87 atoms. In this technique, atomic beams are split and then recombined to produce an interference signal from which the atoms’ gravitational acceleration can be deduced. The team showed that the free-fall acceleration of rubidium-87 atoms of opposite spin is the same to within 1 part in 10 million. The study comes on the heels of other atom interferometry experiments that verified universality of free fall for different atomic species and isotopes to a similar level of precision.

This research is published in Physical Review Letters.

–Ana Lopes

Ana Lopes is a Senior Editor of Physics.


Features

More Features »

Announcements

More Announcements »

Subject Areas

GravitationAtomic and Molecular Physics

Previous Synopsis

Next Synopsis

Fluid Dynamics

Forming Granular Plugs

Read More »

Related Articles

Viewpoint: Black Hole Evolution Traced Out with Loop Quantum Gravity
Particles and Fields

Viewpoint: Black Hole Evolution Traced Out with Loop Quantum Gravity

Loop quantum gravity—a theory that extends general relativity by quantizing spacetime—predicts that black holes evolve into white holes. Read More »

Synopsis: Satellite Mishap Provides Chance for Relativity Test
Gravitation

Synopsis: Satellite Mishap Provides Chance for Relativity Test

Two satellites erroneously placed in elliptical orbits have been used to test general relativity with unprecedented precision. Read More »

Synopsis: Making Mixtures of Magnetic Condensates
Atomic and Molecular Physics

Synopsis: Making Mixtures of Magnetic Condensates

A condensate mixing two species of strongly magnetic atoms provides a new experimental window into many-body phenomena. Read More »

More Articles