Axions and Photons: Quantum Enhancement of Dark Matter Detection Methods.

The search for dark matter and dark energy continues to drive innovation in particle physics, with axions, hypothetical subatomic particles, remaining prime candidates for constituting these enigmatic phenomena. Detecting these weakly interacting particles presents a significant challenge, prompting researchers to explore novel methods for enhancing conversion probabilities between photons and axions, a process facilitated by magnetic fields. A new theoretical framework, detailed in a recent publication, investigates the potential of utilising squeezed coherent states – a type of non-classical light – to amplify this conversion. Taiki Ikeda, Sugumi Kanno, both from Kyushu University, and Jiro Soda from Kobe University, present their findings in the article, “Enhancing photon-axion conversion probability with squeezed coherent states”, demonstrating that the addition of even a modest number of photons within these squeezed states can substantially improve the likelihood of photon-to-axion conversion, offering a potential pathway towards more sensitive axion detection experiments.

Researchers are actively investigating the detection of axions, hypothetical elementary particles considered a leading candidate for dark matter, alongside advancements in gravitational wave detection techniques. A central theme within this research is the exploitation of photon-axion conversion, a process where photons transform into axions and vice versa, as a key mechanism for axion detection. This conversion relies on strong magnetic fields and resonant cavities to enhance the probability of interaction.

Crucially, these investigations emphasise the application of quantum techniques, specifically the utilisation of squeezed states of light, to enhance detection sensitivity. Conventional light possesses inherent quantum noise, limiting the ability to detect faint signals. Squeezed states, however, redistribute this noise, reducing it in the phase of light most sensitive to the axion signal. This reduction effectively lowers the detection threshold, improving the probability of observing the elusive particle. Several studies formulate the photon-axion conversion process within a rigorous field-theoretical framework, demonstrating that squeezed coherent states, containing an added number of photons, significantly boost conversion probability. This enhancement arises from the manipulation of quantum fluctuations, increasing the likelihood of detecting the axion signal and actively addressing the limitations of treating this conversion as a purely classical process.

Beyond axion detection, the research explores innovative approaches to gravitational wave astronomy, particularly for high-frequency gravitational waves. Current gravitational wave detectors, such as LIGO and Virgo, operate most effectively in the lower frequency range. Detecting higher frequency waves requires different technologies. Researchers propose utilising magnons, quantised spin waves in magnetic materials, as a medium for detecting these waves. Theoretical formalisms detail how magnons interact with gravitational waves, causing subtle changes in their properties. Experiments aim to build detectors leveraging this interaction, potentially expanding the observable gravitational wave spectrum. Microwave cavities also feature as potential gravitational wave detectors, utilising resonant amplification to enhance signal detection and providing an alternative pathway for capturing faint signals. The principle relies on the cavity resonating at a specific frequency, amplifying any incoming gravitational wave signal.

This research program actively connects these investigations to early universe cosmology. The properties of axions, including their mass and interaction strength, are intrinsically linked to the conditions prevailing shortly after the Big Bang. Furthermore, the generation of gravitational waves in the early universe, potentially arising from processes like inflation or phase transitions, provides a complementary probe of these conditions. By analysing the characteristics of these primordial gravitational waves, scientists aim to reconstruct the universe’s earliest moments and test cosmological models. For example, the spectrum of primordial gravitational waves can reveal information about the energy scale of inflation.

By combining theoretical modelling, experimental development, and interdisciplinary approaches spanning particle physics, quantum optics, and materials science, this body of work pushes the boundaries of our ability to detect dark matter and explore the universe’s most enigmatic phenomena. The integration of quantum technologies with established detection methods promises to unlock new insights into the fundamental constituents of the universe and the processes that shaped its evolution.