Dark matter is one of the biggest mysteries in science.
Astronomers believe it makes up most of the matter in the universe, yet no one has ever directly seen it.
It does not reflect, emit, or absorb light, which makes it completely invisible to telescopes. Scientists can only tell it exists because of its gravitational pull on stars and galaxies.
Now, researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) are developing powerful new quantum sensing techniques that could finally help detect this elusive substance.
The team is exploring how to measure incredibly tiny signals using the strange rules of quantum physics.
Their work focuses on quantum optical sensing, a method that uses specially prepared light to detect movements so small they would normally be drowned out by noise.
By pushing measurement technology to new limits, the researchers hope to spot signs of dark matter interacting with matter here on Earth.
One approach involves tiny mechanical devices called optomechanical sensors. These devices can be imagined as microscopic drums or membranes that vibrate when a force pushes on them.
Scientists suspect that if dark matter particles pass through Earth, they might cause these membranes to move ever so slightly. Detecting that motion, however, is extraordinarily difficult because the effect would be extremely weak.
To improve sensitivity, the ORNL team uses a special form of light called squeezed light. In quantum physics, even light has natural fluctuations, known as quantum noise, that limit how precisely measurements can be made.
Squeezed light reduces this noise in a controlled way, allowing scientists to measure smaller changes than would otherwise be possible.
The researchers also use entanglement, a phenomenon in which particles of light become linked so that measuring one immediately affects the other, even at a distance. Combining squeezing and entanglement provides a powerful boost in precision.
In their experiment, the scientists used two sensors placed apart from each other and connected them using entangled light beams.
By measuring signals from both sensors together, they were able to detect changes more accurately than with a single sensor alone. Their results show that a network of quantum-connected sensors could act like a giant, ultra-sensitive detector. If dark matter interacts with all sensors simultaneously, the combined measurement would make the signal easier to spot.
This method may be especially useful for searching for a type of dark matter known as ultralight dark matter. Some theories suggest these particles behave more like waves than individual particles.
If such a wave passes through Earth, many sensors could feel it at the same time, producing a shared signal. Averaging the readings from multiple sensors would reduce random noise and highlight the real effect.
The researchers compare the search for dark matter to mapping the ocean floor while looking for a lost ship. Each experiment explores only a small area, and scientists around the world are scanning different regions.
As techniques improve, they can examine smaller details within areas that were once thought empty. Quantum sensing allows scientists to “zoom in” further than ever before, potentially revealing signals that were previously too faint to notice.
Interferometers, instruments that measure tiny changes in waves of light, play a key role in this effort. When combined with quantum-enhanced light, these devices become even more precise. The ORNL team’s work demonstrates that using entangled and squeezed light together can significantly improve the ability to detect extremely weak signals.
Although this research does not yet prove the existence of dark matter, it lays the groundwork for future discoveries.
Finding dark matter would transform our understanding of the universe, from how galaxies formed to the fundamental laws of physics. It could reveal new particles, new forces, or entirely new ideas about how the cosmos works.
For now, scientists continue to refine their tools and techniques, patiently scanning the invisible.
Each improvement brings them a little closer to answering one of humanity’s most profound questions: What is most of the universe actually made of?
