Researchers Forecast Sensitivities to Cosmic Neutrino Background Overdensity Using Large Spin Ensembles

The cosmic neutrino background, a relic of the early universe, represents a fundamental yet elusive target for modern physics, and detecting it poses a significant experimental challenge. Yeray Garcia del Castillo, Giovanni Pierobon, Dipan Sengupta, and colleagues at the Sydney Consortium for Particle Physics and Cosmology now demonstrate a promising pathway towards this goal by modelling how these faint neutrinos interact with ensembles of nuclear spins. Their work extends previous studies by incorporating realistic experimental imperfections into a sophisticated computational framework, allowing them to forecast the sensitivity of future experiments, such as CASPEr, to the density of these relic neutrinos. The results indicate that CASPEr, originally designed to search for dark matter, possesses the potential to constrain the cosmic neutrino background overdensity, offering a novel approach to probing fundamental physics beyond the Standard Model.

Collective Spin Dynamics with Neutrino Interactions

Researchers are investigating the complex behaviour of collective spin systems, groups of atoms or quantum bits acting together, when interacting with neutrinos. This work explores how neutrinos influence the evolution of these systems, focusing on phenomena like superradiance, where the group emits radiation more intensely than individual atoms. The team uses detailed computer simulations to model this interaction, providing insights into the fundamental physics governing these systems and exploring the potential for new quantum technologies.

A collective spin system consists of many two-level quantum systems that interact, with the overall behaviour often more important than that of individual components. Superradiance, a key phenomenon under investigation, arises from the correlated emission of radiation by this collective. The authors validate their simulations by comparing results obtained from both packages, ensuring the accuracy and reliability of their findings.

The simulations demonstrate that collective effects, such as superradiance, significantly influence the system’s dynamics, and neutrino interactions can alter these dynamics, leading to new and potentially observable phenomena. These findings underscore the importance of numerical simulations for understanding complex quantum systems and highlight the value of developing specialised software tools like OpenNu and qutip.

Cosmic Neutrino Detection via Spin Ensembles

Scientists are exploring innovative methods to directly detect the cosmic neutrino background, a faint relic of the early universe predicted to exist alongside the cosmic microwave background. This research focuses on modelling how coherent neutrino interactions affect large, polarised spin ensembles, offering a potential pathway for detection and paving the way for forecasting the sensitivity of future experiments. This approach could provide valuable insights into the properties of these elusive particles and the conditions of the early universe.

Experiments like CASPEr, originally designed to search for axion dark matter, could also be repurposed to constrain the local density of cosmic neutrinos. The results demonstrate that CASPEr, with its current configuration, could limit the neutrino overdensity parameter to approximately 10 9 to 10 11 , and optimising the experiment further could potentially improve this sensitivity down to 10 7 . This research builds upon existing theoretical frameworks and complements other methods used to constrain the cosmic neutrino background.

Current constraints limit the local neutrino overdensity to around 10 11 , but the proposed approach offers a complementary pathway with the potential to reach even greater sensitivities. This research underscores the growing interest in exploring multiple avenues for directly detecting the cosmic neutrino background and furthering our understanding of the universe’s earliest moments.

Neutrino Background Detection with Polarised Spins

Researchers are extending studies of cosmic neutrino background detection by modelling coherent transitions within polarised nuclear spin ensembles. They employ an open system framework and the Lindblad master equation to describe the interactions, incorporating realistic experimental imperfections such as local dephasing and imperfect polarisation. The team developed a computationally efficient method to solve the equation for a large number of spins, enabling them to forecast the sensitivity of future experiments designed to detect these faint signals.

The findings demonstrate that a future experiment, similar to CASPEr, could potentially constrain the cosmic neutrino background overdensity parameter, achieving a sensitivity within currently planned configurations, and even down to in an optimised scenario. This research builds upon existing theoretical frameworks and complements other methods used to constrain the cosmic neutrino background.

Future research could focus on mitigating effects and incoherent local effects that can degrade the signal to further improve sensitivity and explore the feasibility of detecting the cosmic neutrino background with greater confidence. The developed computational methods also provide a valuable tool for modelling and optimising future experiments designed to search for this elusive signal. Continued advancements in quantum sensing technologies are crucial for unlocking the secrets of the universe’s earliest moments.