Dark matter is an elusive substance that is spread across the universe. But, it remains impossible to detect in experiments.
To drastically accelerate the search for one candidate for dark matter in the lab, a team of scientists used an innovative technique called “quantum squeezing.”
Scientists on a project called, fittingly, the Haloscope At Yale Sensitive To Axion Cold Dark Matter (HAYSTAC) experiment report that they’ve improved the efficiency of their hunt past a fundamental obstacle imposed by the laws of thermodynamics. The group includes scientists at JILA, a joint research institute of the University of Colorado Boulder and the National Institute of Standards and Technology (NIST).
The study mainly depends on axion. A theory suggests that axion makes a really good dark matter candidate. Axions are likely billions to trillions of times smaller than electrons. They may have been created during the Big Bang in humungous numbers—enough to explain the existence of dark matter potentially.
Kelly Backes, one of two lead authors of the new paper and a graduate student at Yale University, said, “It’s a doubling of the speed from what we were able to do before.”
Using the new approach, scientists could separate the incredibly faint signals of possible axions from the random noise that exists at extremely small scales in nature, sometimes called “quantum fluctuations.”
Study co-author Konrad Lehnert, a NIST Fellow at JILA, said, “The team’s chances of finding the axion over the next several years are still about as likely as winning the lottery.”
“Once you have a way around quantum fluctuations, your path can just be made better and better.”
Daniel Palken, the co-first author of the new paper, explained that what makes the axion so difficult to find is also what makes it such an ideal candidate for dark matter—”it’s lightweight, carries no electric charge, and almost never interacts with normal matter.”
“They don’t have any of the properties that make a particle easy to detect.”
“But there’s one silver lining: If axions pass through a strong enough magnetic field, a small number of them may transform into waves of light—and that’s something that scientists can detect.”
Scientists have launched efforts to find those signals in powerful magnetic fields in space. The HAYSTAC experiment, however, is keeping its feet planted on Earth. The experiment uses an ultra-cold facility on the Yale campus to create strong magnetic fields, then try to detect the signal of axions turning into light. It’s not an easy search.
Scientists have predicted that axions could exhibit an extremely wide range of theoretical masses, each of which would produce a signal at a different frequency of light in an experiment like HAYSTAC. To find the real particle, then, the team may have to rifle through a large range of possibilities—like tuning a radio to find a single, faint station.
Palken said, “If you’re trying to drill down to these feeble signals, it could end up taking you thousands of years.”
The laws of quantum mechanics themselves, specifically Heisenberg Uncertainty Principle acts as the biggest obstacle- it restricts how accurate scientists can be in their observations of particles.
In this case, the team can’t accurately measure two different properties of the light produced by axions simultaneously.
The trick comes down to using a tool called a Josephson parametric amplifier. Scientists developed a way to use these small devices to “squeeze” the light they were getting from the HAYSTAC experiment.
Palken explained that the HAYSTAC team doesn’t need to detect both properties of incoming light waves with precision—just one of them. Squeezing takes advantage of that by shifting uncertainties in measurements from one of those variables to another.
“Squeezing is just our way of manipulating the quantum mechanical vacuum to put ourselves in a position to measure one variable very well. If we tried to measure the other variable, we would find we would have very little precision.”
Scientists tested their method by running a trial at Yale. They explored the particle over a specific range of masses. They didn’t find it, but the experiment took half the time than it usually would.
Backes said, “We did a 100-day data run. Normally, this paper would have taken us 200 days to complete, so we saved a third of a year, which is pretty incredible.”
Lehnert added that the group is eager to push those bounds even farther—coming up with new ways to dig for that ever-elusive needle.
“There’s a lot of meat left on the bone in just making the idea work better.”