Could Gravitational Waves Be Detectable With a Single Atom?

A new paper from Stockholm University lays out an intriguing idea: What if the spontaneous radiation emitted by single atoms is actually affected by passing gravitational waves? And what if those effects could be read out to create a detection of the gravitational wave in question?
Let’s go back to the nature of current gravitational wave detectors. Right now, there are detectors all over the planet that use laser interferometry to detect nanometer-scale movements. Using this approach, scientists can detect tiny movements and vibrations caused by passing gravitational waves—but only when comparing two detections taken at the same instant.
As a result, LIGOs (Laser Interferometer Gravitational-Wave Observatories) are now all over the world. In principle, the size of the overall LIGO detector (or the sum of these parts) is equal to the distance between each observatory, which means that the largest possible terrestrial detector would be the diameter of the Earth itself.
LIGO has led to an incredible uptick in the pace of new discoveries, but it’s also limited by Earth’s physical size. To detect the largest waves, produced by larger events, detectors have had to get bigger, too.
That is what led to the ESA’s latest big project: the Laser Interferometer Space Antenna, or LISA. LISA aims to increase the distance between the detectors by putting them both on satellites orbiting not the Earth, but the Sun. In so doing, they hope to put the detectors a cool million kilometers apart.
But that requires a different type of detector than the ones back on Earth, bringing us to the astonishing level of effort required to create a gravitational wave detector that will work in space. To make an interferometer work in a moving system like two orbiting spacecraft, the team has had to figure out how to float a weight in 100% flawless sync with the spacecraft around it, serving as a “test mass” to prove perfect free-fall.
Using these test masses, the satellites can coordinate well enough to enable laser interferometry at up to a million times the scale of one on Earth. The overall project to launch and coordinate two such detectors on two satellites could take as long as 40 years from inception to completion.
Here, we turn to the more recent paper on spontaneous atomic emissions, which proposes that deviations in emission frequency could reveal much the same information as a laser interferometer. It would also, crucially, work just fine in space.
This idea would require taking multiple readings over time to monitor the wave’s progression as it passes, but each detector could also be much smaller and, potentially, simpler. Each of LIGO’s interferometers is kilometers long, and each of LISA’s orbiting detectors is obscenely difficult to construct, while this idea focuses on collecting known types of radiation from nano-scale objects.
Right now, this is a theory paper. A detector implementing this idea has yet to be built, even as a proof-of-concept, but the sheer difficulty of existing efforts makes it worth actively pursuing as soon as possible.
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