Scientists are developing a new, faster method to detect dark matter

For nearly a century, scientists have worked to unravel the mystery of dark matter – an elusive substance that spreads throughout the universe and is likely to make up much of its mass, but so far cannot be discovered in experiments. Now a team of researchers has used an innovative technique called “quantum squeezing” to dramatically speed up the search for a dark matter candidate in the laboratory.

The findings, published today in the journal Nature, centered on an incredibly lightweight and yet undiscovered particle called the axion. According to the theory, axions are likely billions to trillions times smaller than electrons and could have been created in gigantic numbers during the Big Bang – enough to possibly explain the existence of dark matter.

Finding this promising particle, however, is a bit like looking for a single quantum needle in a very large haystack.

There may be some relief in sight. Researchers on a project called, appropriately, the Haloscope At Yale Sensitive To Axion Cold Dark Matter (HAYSTAC) experiment report that they have improved the efficiency of their hunt beyond a fundamental obstacle imposed by the laws of thermodynamics. The group includes scientists from JILA, a joint research institute of the University of Colorado Boulder and the National Institute of Standards and Technology (NIST).

“It’s doubling the speed of what we could before,” said Kelly Backes, one of the new paper’s two lead authors and a graduate student at Yale University.

The new approach allows researchers to better separate the incredibly weak signals from possible axions from the random noise that exists in nature on extremely small scales, known as “quantum fluctuations”. The team’s chances of finding the axion in the coming years are still about as likely as winning the lottery, said study co-author Konrad Lehnert, a NIST Fellow at JILA. But those opportunities are only getting better.

“Once you’ve found a way to get around quantum fluctuations, your path can just keep getting better,” said Lehnert, also an adjunct professor in the department of physics at CU Boulder.

HAYSTAC is led by Yale and is a partnership with JILA and the University of California, Berkeley.

Quantum Laws

Daniel Palken, the co-lead author of the new paper, explained that what makes the axion so difficult to find also makes it such an ideal candidate for dark matter – it’s lightweight, carries no electrical charge, and almost never interacts with normal matter. .

“They don’t have any of the properties that make a particle easy to detect,” says Palken, who are Ph.D. from JILA in 2020

But there’s one silver lining: If axions pass through a strong enough magnetic field, a small number of them can turn into light waves – and that’s something scientists can detect. Researchers have made attempts to find those signals in powerful magnetic fields in space. The HAYSTAC experiment, however, keeps its feet planted.

The project, which published its initial findings in 2017, uses an ultra-cold facility on the Yale campus to create strong magnetic fields and then detect the signal from axions turning into light. It is not an easy quest. Scientists have predicted that axions could exhibit an extremely wide range of theoretical masses, each of which would produce a signal with a different light frequency in an experiment like HAYSTAC. To find the real particle, the team may need to sift through a myriad of possibilities – such as tuning a radio to find a single, weak station.

“If you try to get to these really weak signals, it could take thousands of years,” Palken said.

Some of the biggest obstacles the team faces are the laws of quantum mechanics themselves, namely the Heisenberg uncertainty principle, which limits how accurate scientists can be in their observations of particles. In this case, the team cannot accurately measure two different properties of the light produced by axions at the same time.

However, the HAYSTAC team has landed in a way to slip past those immutable laws.

Shifting uncertainties

The trick boils down to using a tool called a Josephson parametric amplifier. JILA scientists have developed a way to use these tiny devices to “squeeze” the light they received from the HAYSTAC experiment.

Palken explained that the HAYSTAC team does not need to accurately detect both properties of incoming light waves – just one of them. Squeezing responds to this 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,” Palken said. “If we tried to measure the other variable, we would find that we would have very little precision.”

To test the method, the researchers took a test drive at Yale to find the particle over a specified range of masses. They didn’t find it, but the experiment took half the time than usual, Backes said.

“We performed a 100-day data run,” she said. “Normally it would take us 200 days to complete this paper, so we saved a third of a year, which is pretty incredible.”

Lehnert added that the group is eager to push those boundaries even further – invent new ways to dig for that ever-elusive needle.

“A lot of meat is left on the bone to make the idea work better,” he said.