A team of physicists at Stockholm University has put forward a groundbreaking proposal: a method to detect single gravitons. Interestingly, “these elusive particles were assumed to be too hard to observe” until now.
For context, gravitons are theoretical particles believed to be the building blocks of gravity. Scientists have long been striving to bridge the gap between gravity and quantum mechanics.
“If we believe in quantum theory, even gravity must be made of tiny, quantized particles – gravitons,” says the researchers.
But “single gravitons barely interact with anything at all. They pass nearly all matter as they cross the universe. Detecting them seemed impossible,” the researchers added in a press release.
The proposed solution
Now, the research team, led by Stevens physics professor Igor Pikovski, has “worked out how to build a single-graviton-detector” that could enable the detection of gravitons .
Their method leverages the recent progress in the field of quantum sensing and the study of macroscopic quantum objects.
These objects, large enough to be seen with the naked eye yet displaying quantum behavior, are ideal for detecting gravitons due to their strong interaction with gravity.
The team’s proposal builds upon existing technologies, such as acoustic resonators and Weber bars.
The detector functions by cooling a macroscopic quantum object to its lowest energy state and then exposing it to gravitational waves.
“We need to cool the material and then monitor how the energy changes in a single step, and this can be achieved through quantum sensing,” explained postdoctoral researcher Sreenath Manikandan.
The “gravito-phononic effect”
The scientists hypothesize that when a graviton interacts with the object, it will cause a discrete change in its energy, a phenomenon they call a “quantum jump.”
This distortion is usually too tiny to notice, but by meticulously monitoring these quantum jumps, the team believes they can pinpoint the absorption of a single graviton.
This “gravito-phononic effect” mirrors the photoelectric effect, where light interacts with matter in discrete steps or photons.
“Our solution mimics the photoelectric effect, but we use acoustic resonators and gravitational waves that pass Earth,” said PhD student Germain Tobar. “We call it the ‘gravito-phononic’ effect.”
Utilizing LIGO data
To increase their chances of detecting gravitons, the team suggests using data from the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO is renowned for its groundbreaking detection of gravitational waves , but it cannot directly detect individual gravitons.
Notably, as per the team, detecting a single graviton requires extremely energetic gravitational waves. This is because the interaction between a single graviton and matter is expected to be incredibly weak.
Besides, we can’t simply create gravitational waves whenever we want in a lab. They are produced by massive cosmic events like colliding black holes or neutron stars.
However, by meticulously correlating LIGO’s data with their proposed detector’s measurements, the researchers believe they can isolate and confirm the signature of a single graviton interaction.
“We can solve both problems by using existing gravitational wave observatories,” asserted PhD student Thomas Beitel.
“We wait until LIGO detects a passing gravitational wave and observe how it produces quantum jumps in our detector at the same time.”
Quest for unified theory
While the theoretical framework of the experiment is robust, the technology to detect these gravitons remains a formidable challenge. The required level of quantum sensing capabilities is yet to be fully developed.
That said, the team is optimistic and is now focused on designing a concrete experiment using data from gravitational waves detected on Earth.
The research on detecting gravitons has been ongoing for over a century. Einstein’s theory of relativity revolutionized our understanding of gravity, describing it as a curvature of spacetime.
However, gravity remains the only fundamental force that hasn’t been fully explained by quantum theory. The successful detection of a graviton would mark a significant step toward a unified “theory of everything.”
Local News
