Scientists develop new, faster method of finding dark matter

Scientists have been working for almost a century to unravel the mystery of dark matter – an elusive substance that spreads throughout the universe and probably makes up much of its mass, but has so far proved impossible to detect in experiments. Now a team of researchers has used an innovative technique called ‘quantum squeezing’ to dramatically speed up the search for one candidate for dark matter in the laboratory.

The findings, published today in the journal Nature, centers on an incredibly lightweight and yet undiscovered particle called the action. According to the theory, actions are probably billions to trillions of times smaller than electrons and were created in large numbers during the big bang – enough to explain the existence of dark matter.

However, finding this promising particle is just like searching for a single quantum needle in one big haystack.

There may be some relief in sight. Researchers of a project called the Haloscope At Yale Sensitive To Axion Cold Dark Matter (HAYSTAC) experiment report that they have improved the efficiency of their hunting, 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 a doubling of the speed we were able to do before,” said Kelly Backes, one of the two lead authors of the new article and a graduate student at Yale University.

The new approach enables researchers to better separate the incredibly faint signals of possible action from the random noise that exists on extremely small scales in nature, sometimes also called “quantum fluctuations”. The chance that the team will find the action in the next few years is still as likely as winning the lottery, said Konrad Lehnert, a NIST fellow from JILA. But the chances are only going to get better.

“Once you have a way of quantum fluctuations, your path can only get better and better,” said Lehnert, also a 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 Law

Daniel Palken, co-author of the new article, explained that the action is so hard to find, also making it the ideal candidate for dark matter – it is lightweight, carries no electric charge and almost never works with normal matter does not interact.

“They do not have any of the properties that a particle can easily detect,” Palken said. from JILA in 2020

But there is one silver lining: if actions move through a strong enough magnetic field, a small number of them can turn into waves of light – and this is something scientists can detect. Researchers have made efforts to find the signals in powerful magnetic fields in space. However, the HAYSTAC experiment keeps its feet planted on the ground.

The project, which published its first findings in 2017, uses an ultra-cold facility on the Yale campus to create strong magnetic fields, and then attempts to detect the signal of actions changing into light. This is not an easy search. Scientists have predicted that actions can display a very wide range of theoretical masses, each of which will deliver a signal at a different light frequency in an experiment such as HAYSTAC. To find the right particle, the team may then have to go through a wide range of possibilities, such as turning off a radio to find a single, dim station.

“If you try to drill down to these weak signs, it can take thousands of years,” Palken said.

Among the biggest obstacles the team faces are the laws of quantum mechanics itself, 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 actions simultaneously.

However, the HAYSTAC team ended up in a way of slipping past the unchanging laws.

Uncertainties shift

The trick comes down to using a tool called a Josephson parametric amplifier. JILA scientists have developed a way to use these small devices to “print” the light they receive from the HAYSTAC experiment.

Palken explained that the HAYSTAC team does not need to detect both characteristics of incoming light waves with precision – just one of them. Persing exploits this by shifting uncertainties in the measurements from one of the variables to another.

“Pressing is just our way of manipulating the quantum mechanical vacuum to enable us 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 conducted a test run on Yale to search for the particle over a certain mass of mass. They did not find it, but the experiment took half the time it would normally do, Backes said.

“We did a 100-day data run,” she said. “Normally this paper would have taken us 200 days to complete, so we saved a third of a year, which is quite incredible.”

Lehnert added that the group is eager to push these boundaries even further – with new ways to dig into that ever-elusive needle.

“There’s a lot of meat left over to make the idea work better,” he said.