Researchers boost dark matter detection using nuclear spins and superradiance with scaling rates

The search for dark matter and other elusive cosmic relics receives a significant boost from new research demonstrating a pathway to dramatically enhance detection rates using the collective behaviour of atomic nuclei. Marios Galanis, from the Perimeter Institute for Theoretical Physics, Onur Hosten of the Institute of Science and Technology Austria (ISTA), and Asimina Arvanitaki, also at the Perimeter Institute, alongside Savas Dimopoulos from the Leinweber Institute for Theoretical Physics at Stanford, present a protocol that achieves an unprecedented level of signal amplification. Their work leverages a process akin to superradiance, where the combined effect of numerous nuclear spins dramatically increases the interaction with weakly interacting particles, potentially revealing the existence of dark matter candidates like axions and dark photons. The team demonstrates a method to achieve 48 decibels of ‘spin squeezing’, effectively magnifying the signal by a factor of over 250, and paving the way for ultra-sensitive detectors capable of probing the faintest interactions from cosmic sources, including the elusive cosmic neutrino background.

Clear spin ensembles prepared in coherent spin states can dramatically enhance the interaction rates of weakly interacting cosmic relics, such as dark matter and the cosmic neutrino background, through collective quantum effects analogous to Dicke superradiance, where the de-excitation and excitation rates scale as the square of the number of spins, N. These processes are termed superradiant interactions. The spins are first initialised, and then manipulated to create a collective quantum state optimised for detecting these faint signals.

Spin Squeezing Beats Standard Quantum Limit

Researchers are striving to overcome the fundamental limits of precision in measurement, a barrier known as the standard quantum limit. This work describes a method for achieving higher precision using large groups of spins, such as those found in atoms or nuclei, to reduce measurement noise and amplify signals from distant or weakly interacting sources. This is achieved by a technique called ‘squeezing’, which reduces uncertainty in one aspect of the spin state at the expense of another, and by carefully controlling potential sources of error. The analysis identifies several factors that can degrade measurement precision, including mechanical vibrations, thermal fluctuations, and imperfections in radiofrequency signals.

The collective behaviour of the spin ensemble, specifically spontaneous emission, also contributes to noise. The team carefully models these noise sources and develops strategies to mitigate their effects. The results demonstrate that measurement precision is strongly influenced by the stability of the experimental setup and the quality of the radiofrequency signals. There is an upper limit to the number of spins that can be used effectively; simply adding more spins does not always improve precision. This detailed analysis provides valuable insights into the factors limiting precision in spin-based measurements and guides the development of more sensitive experimental designs.

Spin Ensembles Amplify Weak Cosmic Signals

Researchers have demonstrated a groundbreaking method for enhancing the detection of weakly interacting cosmic relics, such as dark matter and the cosmic neutrino background, by leveraging the collective behavior of nuclear spins. This innovative approach, termed “superradiant interactions,” dramatically amplifies signals that would otherwise be too faint to detect, potentially revolutionizing searches for these elusive components of the universe. The team achieved this enhancement by preparing macroscopic ensembles of nuclear spins in a coherent state and coupling them to superconducting circuits, creating a system where interaction rates scale with the square of the number of spins. Experiments revealed that this protocol can reduce the standard variance of spin measurements by up to 4.

8 orders of magnitude, equivalent to 48 decibels of squeezing, for circuits exhibiting quality factors exceeding 10 6 . This extraordinary level of squeezing is achieved through a carefully orchestrated process involving initialization of the spins and manipulation of the spin-circuit interaction, effectively minimizing quantum noise. The data demonstrates that this squeezing can be further utilized to magnify the imprinted signal, easing the requirements for highly sensitive readout systems. This breakthrough delivers a significant boost to the potential of axion and dark photon dark matter searches, extending the reach of existing experiments to probe previously inaccessible couplings. Furthermore, this technique paves the way for detecting coherent inelastic interactions from other cosmic relics, most notably the cosmic neutrino background, establishing nuclear-spin-based systems as a new class of ultra-low-threshold detectors. By manipulating the system’s energy levels and exploiting the collective behavior of the spins, researchers have created a powerful tool for unraveling the mysteries of the universe and probing the fundamental nature of dark matter and other elusive phenomena.

Squeezed Spins Enhance Relic Signal Detection

The research demonstrates a novel method for enhancing interactions with weakly interacting cosmic relics, such as dark matter and the cosmic neutrino background, by leveraging collective effects within macroscopic nuclear spin ensembles. By initializing these ensembles into coherent spin states and coupling them to superconducting circuits, the team achieved significant squeezing of the spin system, reducing variance by up to 48 decibels. This squeezing amplifies the potential for detecting subtle signals from these elusive relics, potentially accelerating searches for axions and dark photons and opening avenues for detecting the cosmic neutrino background. The protocol relies on carefully controlling the interaction between the nuclear spins and the superconducting circuits, favouring systems with large ensembles and high-quality circuits to overcome spin relaxation and dephasing.

The results show a substantial improvement in sensitivity, although the authors acknowledge limitations stemming from approximations made in modelling the system, such as assuming linear magnetic field gradients and small spin displacements. Future work will focus on refining these models and exploring the practical challenges of implementing this technique in real-world experiments, potentially leading to a new class of ultra-low-threshold detectors for cosmic relics. This research represents a significant step towards unlocking the secrets of the universe and understanding the nature of dark matter and other elusive phenomena.