Is it possible to manipulate dark matter?

Dark matter: "Quantum press" helps with the Axion search

Heisenberg's uncertainty tricked: Researchers have developed a method that could significantly advance the search for dark matter particles. Because with the help of a “quantum press” they circumvent the limits set by Heisenberg's uncertainty and quantum fluctuations. Among other things, this technology makes the HAYSTAC detector more sensitive to signals from axions - the currently favored candidates for dark matter particles.

What is dark matter made of? Physicists have been puzzling over this question for almost 100 years. There are plenty of candidates for possible particles of this exotic form of matter - the spectrum ranges from weakly interacting massive particles (WIMPs) to dark bosons and particles with exotic quark combinations and to rather lightweight candidates such as sterile neutrinos or the currently favored axions.

Search for axions

Axions are hypothetical elementary particles that are billions of times lighter than an electron and have no charge or spin. In addition, these particles hardly interact with normal matter and are therefore only noticeable through their collective gravitational effects - according to the theory. Too bad: "The axions do not have any of the properties that make it easy to find a particle," explains co-first author Daniel Palken from the JILA Institute at the University of Colorado.

However, there is one feature that could give the axions away: when they fly through a strong magnetic field, a small fraction of them interact with the electromagnetic field and form a photon. These tiny light signals can be amplified in special resonator chambers and thus made visible to highly sensitive detectors. One of these detectors is the HAYSTAC experiment in New Haven.

"Squeezing" against quantum noise

But the previous axion detectors have a big problem: The light signals of the axions are so weak that they are largely drowned in the quantum noise. In addition, Heisenberg's uncertainty principle prevents the researchers from recording both the position and the energy of the resulting photons with the same precision - according to the principle, only one of them works because the measurement changes the parameters.

Palken, Kelly Backes from Yale University and their colleagues have now found a solution. They developed a technique by which the light from the HAYSTAC resonator is “squeezed” quantum-physically. The quantum fluctuations are increased in the case of a feature of the light signals that is not required for the measurement, as a result of which the noise in another feature is pushed below the otherwise applicable quantum limit.

A similar “quantum press” has already increased the sensitivity of the LIGO gravitational wave detectors and made it possible for physicists to detect even the macroscopic effects of quantum noise.

More sensitivity and bandwidth

“With squeezing, we can manipulate the quantum mechanical vacuum in such a way that we can measure a variable in our signal very precisely,” explains Palken. “However, if we wanted to measure the other variable, we would find very little precision.” Specifically, the “squeezing” of the light achieved on the HAYSTAC detector means that the quantum noise for the relevant parameter is reduced by four decibels.

As a result, the researchers can now detect such light signals over a broad bandwidth with greater sensitivity. This in turn increases the chances of capturing the rare signal of a transformed axion in less time. "It doubles our previous search speed," says Backes. In an initial test, the team only needed 100 instead of 200 days to search a specific energy range for axion signals.

First step towards further optimization

According to the researchers, the quantum physical "upgrade" of detectors increases the chances of a future detection of axions considerably. "Our work demonstrates that the incompatibility of sensitive quantum technology and harsh practice in the search for new particles can be overcome," said Backes and her colleagues.

Igor Irastorza from the University of Zaragoza sees it similarly. In an accompanying comment in “Nature” he writes: “This improvement may seem relatively small, but it paves the way for further advances in sensitivity. Depending on the quality of the squeezing, almost unlimited improvements are possible. ”The work of Backes and team is therefore an important first step towards quantum-optimized particle searches. (Nature, 2021; doi: 10.1038 / s41586-021-03226-7)

Source: University of Colorado at Boulder

February 11, 2021

- Nadja Podbregar