Dark matter: “Quantum press” cooperates Axion search

Dark matter: “Quantum press” cooperates with the Axion search. Squeezed light makes the detector more sensitive to signals from dark matter particles.

The previously hypothetical axions could be detected with strong magnetic fields – if the detectors suppress the quantum noise. That is better possible in the future.

Heisenberg’s Uncertainty Tricked

Researchers have produced a method that could significantly improve the search for the bits of dark matter. Because with the guidance of a “quantum press” they circumvent the deadlines set by Heisenberg’s uncertainty and quantum fluctuations. Among other things, this technology offers the HAYSTAC detector more sensitive to signals from axions – the currently favoured candidates for dark matter scraps.

What is dark matter made of? Physicists have been perplexing over this question for approximately 100 years. There are plenty of candidates for permissible particles of this fascinating form of matter. The spectrum ranges from weakly communicating massive particles (WIMPs) to dark bosons and particles with strange quark combinations and relatively lightweight candidates such as sterile neutrinos or the currently favoured axions.

Search for Axions

Axions are hypothetical fundamental particles that are billions of times more moderate than an electron and have no charge or spin. According to the theory, these particles hardly interact with ordinary matter and are, therefore only noticeable through their collective gravitational effects. “The axions do not possess any of the characteristics that make it easy to find a particle,” explains co-first author Daniel Palken from the JILA Institute at the University of Colorado.

However, one feature could give the axions away: when they fly through a strong magnetic field, a small division of them interact with the electromagnetic field and create a photon. These tiny light signals can be augmented in extraordinary resonator chambers and made visible to sensitive detectors. One of these indicators is the HAYSTAC agreement in New Haven.

“Squeezing” against Quantum Noise

But the preceding axion detectors have a big problem: The axions’ light signals are so weak that they are primarily drowned in the quantum noise. Besides, Heisenberg’s uncertainty principle prevents the researchers from recording both the position and the resulting photons’ energy with the same precision – according to the regulation, 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 enhanced in the case of a feature of the light signals not required for the measurement. The noise in another feature is pushed beneath the otherwise appropriate quantum limit.

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

Added Sensitivity and Bandwidth

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

As a result, the researchers can now recognize such light signals over a broad bandwidth with greater sensitivity. This, in turn, increases the chances of capturing a transformed axion’s rare gesture in less time. “It doubles our previous search rate,” says Backes. In an initial test, the team only needed 100 instead of 200 days to search for 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 future detection of axions considerably. “Our work demonstrates that it can overcome the incompatibility of sensitive quantum technology and harsh practice in the search for new particles,” 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 insensitivity. Depending on the quality of the squeezing, improvements of almost any size are possible.” The work of Backes and team is, therefore, an essential first step towards quantum-optimized particle searches.