Dark matter: the strategic role of quantum sensing in modern particle physics

 Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) are currently spearheading innovative efforts to facilitate the discovery of dark matter. By pioneering novel measurement approaches within the quantum realm and utilizing sophisticated quantum optical sensing techniques, ORNL scientists are developing the essential methodologies required to transcend conventional observational limits. Their primary objective is to detect this enigmatic and invisible substance that appears to permeate the entire universe.

Advancements in dark matter research at oak ridge national laboratory

ORNL remains committed to fostering an innovative quantum future while simultaneously enhancing national energy security and competitiveness. By leveraging extensive institutional expertise, the laboratory is engineering solutions that are more secure, efficient, and reliable at the quantum scale. Advanced quantum sensing capabilities hold the transformative potential to reveal previously unobservable phenomena, ranging from novel material properties to the most fundamental constituents of the physical universe.

In a significant technical achievement, researcher Claire Marvinney and Group Leader Alberto Marino of ORNL’s Quantum Sensing and Computing Group, in collaboration with international colleagues from South Korea, have successfully executed a distributed sensing experiment. The team utilized a two-mode squeezed light source integrated into a nonlinear interferometric configuration to measure two optical phase shifts. This process relied on the strategic reduction of quantum noise to achieve unprecedented levels of precision.

The research further involved a theoretical expansion from a two-mode system to an M-mode configuration. This distributed and entangled sensing setup allows for the measurement of parameters across geographically separated sensors with an accuracy that surpasses established classical limits. The results demonstrated that this entangled multi-sensor approach provides a quantum measurement enhancement that exceeds the capabilities of single-mode squeezing alone, marking a pivotal step forward in the detection of subtle cosmic signals.

The role of optomechanical sensors in dark matter detection

According to Alberto Marino, optomechanical sensors function similarly to microscopic membranes or drums that oscillate in response to external forces. The underlying hypothesis suggests that dark matter interacts with these membranes, causing subtle displacements. By utilizing laser light to illuminate these structures, researchers can monitor their motion with extreme precision. The integration of quantum light—specifically squeezed light, which possesses reduced noise properties—significantly enhances the sensitivity of these measurements, allowing for the detection of movements that would otherwise remain obscured.

Despite the prevailing theory that dark matter constitutes the vast majority of the universe's mass, its constituent particles remain hypothetical. Because dark matter does not interact with electromagnetic radiation, it is effectively invisible to traditional telescopes and light-based detection instruments. Its presence is inferred solely through its gravitational influence on visible celestial objects. Consequently, classical detection methods lack the necessary sensitivity to identify these elusive particles, necessitating a transition toward quantum-enhanced methodologies.

The research team successfully utilized a distributed network of two sensors by exploiting two primary quantum resources: squeezing and entanglement. Squeezing refers to the reduction of quantum noise below the classical optical limit, while entanglement involves the establishment of complex quantum correlations between optical beams. Researcher Claire Marvinney emphasized that achieving the sensitivity thresholds required for dark matter detection is impossible through classical means; therefore, these quantum resources provide a demonstrable advantage in proof-of-principle experiments.

The implemented detection scheme employs optomechanical systems to measure the collective signal across multiple independent sensors. By utilizing entangled light to monitor these minute mechanical movements, the system can determine the average signal from the entire network. This collective approach enhances sensitivity to distributed signals that interact with all sensors simultaneously, far exceeding the capabilities of isolated measurement devices.

The ongoing efforts are specifically tailored to search for ultralight dark matter, a candidate with a mass as small as ten-billionths of a trillionth of an electron's mass. Theoretical models suggest that this form of dark matter behaves more like a wave than a particle. In high-density environments, this bosonic dark matter would interact collectively with an array of sensors, producing a uniform signal across the entire network.

By developing techniques to detect these waves through a hypothesized "fifth force" interaction, the researchers are aligning their work with established theoretical frameworks such as the 2022 Snowmass Windchime white paper. The use of a two-mode squeezed light source, where modes are entangled directly at the origin, represents a novel frontier in quantum sensing. These advancements pave the way for ultra-sensitive phase measurements that could eventually confirm the existence of dark matter and provide a deeper understanding of the post-Big Bang universe.

The precision of interferometry in particle physics

The pursuit of infinitesimal particles demands both rigorous instrumentation and profound patience. Interferometers serve as the primary tools for such high-precision measurements, capable of identifying minute fluctuations in wave interference patterns caused by the displacement of a mirror. By observing these subtle shifts, researchers can infer the presence of particles or fields interacting with the sensory apparatus. These instruments act as the foundational architecture upon which more complex quantum enhancements are built.

While classical interferometry provides a baseline for measurement, quantum sensing approaches incorporating squeezing and entanglement offer a level of precision that transcends traditional limitations. By utilizing squeezed light, which exhibits reduced quantum noise, and further leveraging entanglement within the sensor's probing light, scientists can dramatically improve joint measurement sensitivity. This quantum advantage is essential for detecting exceptionally weak signals that were previously unobservable, thereby deepening the scientific understanding of fundamental particle behavior.

The search for dark matter is often compared to mapping a vast seabed in a grid pattern to locate a lost vessel. In this international effort, various research teams examine individual squares within the grid, systematically eliminating regions where the elusive particles are not found. However, increasing the sensitivity within a single square—much like sharpening the resolution of a sonar image—allows for the detection of even smaller fragments. By reducing noise through nonlinear interferometry, the ORNL team has effectively magnified their "viewing area," enabling the observation of features that were once considered too small to be perceived.

A critical component of this enhanced sensitivity is the use of a two-mode squeezed state, which consists of two entangled optical beams. The quantum correlations between these beams result in a significant reduction of noise during joint measurements. Alberto Marino explains that this squeezing property is harnessed to suppress background interference, thereby making the optomechanical sensors far more responsive. By probing these sensors with entangled states, the researchers can improve the signal-to-noise ratio, revealing faint cosmic signatures that might represent the fragmented "pieces" of the dark matter puzzle.

This meticulous reductive process ensures that even the most minute characteristics within the analyzed quadrant can be highlighted. As researchers continue to refine these quantum resources, they move closer to identifying signals that have historically remained below the detection threshold. The integration of entanglement not only refines current measurements but also sets a precedent for future experiments, providing a clearer and more detailed map of the physical world at its most fundamental level.

Collective measurement in quantum sensor arrays

According to Alberto Marino, the management of sensor arrays can be approached through two distinct quantum methodologies. The first involves analyzing each sensor independently using individual quantum states of light to achieve noise reduction. However, a more advanced strategy leverages entanglement to establish quantum correlations across multiple sensors—or optical beams—enabling a collective measurement. This integrated approach facilitates a significantly greater quantum enhancement than what could be achieved by treating each component in isolation.

The eventual detection of dark matter is expected to catalyze a transformative shift in the scientific landscape, whether it reveals previously unimagined particles, refines the current understanding of gravity, or provides new insights into the mechanics of black holes. Such a breakthrough would likely resolve long-standing mysteries across the fields of astronomy and galactic formation, offering a clearer picture of the invisible forces that govern the behavior of infinite particles. Ultimately, these findings are poised to alter the Standard Model of physics and fundamentally rewrite the collective human understanding of the cosmos.

Marino emphasizes that while the ultimate goal remains the direct detection of dark matter, the current priority is the development of the necessary technical foundations. This phase of research focuses on fundamental experiments and proof-of-concept demonstrations that serve as the bedrock for future discovery. Although this initial "seabed mapping" approach is inherently meticulous and time-intensive, each incremental advancement in measurement tools—such as squeezing and entanglement—progressively sharpens the sensitivity of the search.

The confirmation of dark matter will do more than just explain the birth of the universe; it will provide a comprehensive catalog of its most elusive components. As Claire Marvinney notes, this research is instrumental in helping the scientific community grasp fundamental physics and the existence of additional particles and forces. These ongoing advancements in quantum sensing represent a critical step toward unveiling the governing principles of reality and the hidden structures that define the physical world.

The study is published in the journal Physical Review Research.