2D quantum crystal sensor could chase dark matter particles
Dark matter should be all around us, but dark matter is frustrating and elusive. Today, physicists at the National Institute of Standards and Technology (NIST) have developed a new sensor that could help us detect certain hypothetical dark matter particles, using a two-dimensional quantum crystal.
Decades of astrophysical observations suggest that there is much more mass in the cosmos than we can see. This has led scientists to hypothesize that the universe is dominated by a strange substance that we call dark matter, which does not reflect, refract or interact in any way with light, and only influences ordinary matter. by its strong gravitational pull.
In space, observational evidence of this stuff keeps piling up, but it’s hard to spot it directly. And it’s not for lack of trying – experiments are constantly being offered or conducted, designed to detect different candidate particles based on the different properties they may or may not have. Many use huge underground reservoirs filled with fluids that could detect a collision by a passing dark matter particle, while others could chase their gravitational pull on tiny pendulums.
One of the main candidates is a hypothetical particle called an axion. The models suggest that the axions have a neutral electric charge, have almost no mass, drift in waves and, most importantly, have weak influences on electromagnetism. Experiments have looked for this type of interaction using “axionic radios”, quantum bits in cavities or donut-shaped magnets.
And now the NIST team has developed a new type of axionic sensor. It’s made up of 150 beryllium ions trapped inside a magnetic field, forcing them to organize into a flat plane just 200 microns thick. When exposed to an electric field, the plane of atoms would move up and down like a drum – so if they are isolated from any external electric field, spotting this movement could indicate that an axion or a other dark matter particle has passed through.
The team claims the sensor would be 10 times more sensitive than other similar experiments, capable of detecting an electric field of 240 nanovolts per meter in one second. This might help him spot axions over a wider range of frequencies.
This extra sensitivity comes from the frightening world of quantum physics. Any displacement an axion would have on the ions would be extremely small and difficult to measure, so the researchers used quantum entanglement to amplify the signal.
The team zapped the ions with intersecting laser beams, causing the movement of the ions to become inextricably linked to an electronic property called “spin.” All the ions were made to spin “up”, so that any change in their collective rotation could reveal any shift in their motion, caused by an axion. And conveniently enough, measuring their spin is relatively easy – if the ions are in a spin up state, the crystal will fluoresce, but if they are in a spin down state, it will remain dark.
The fluorescence of this quantum crystal can then reveal whether an axion has passed through the instrument.
The researchers say that future work could improve the detector’s sensitivity 30 times, by making 3D crystals containing 100,000 ions. If this experience ever joins the hunt for dark matter, it could help unravel one of the most enduring cosmic mysteries.
The research was published in the journal Science.