Superradiant Interactions of Weakly Interacting Particles with Matter

Core Concepts

Coherent inelastic interactions, termed "superradiant interactions," offer a novel approach to detecting weakly interacting particles like the Cosmic Neutrino Background and dark matter by significantly enhancing interaction rates and providing new observables beyond traditional energy exchange.

Abstract

This research paper explores the potential of superradiant interactions for detecting weakly interacting particles. The authors establish the conditions for achieving macroscopic coherence in inelastic scattering processes, drawing parallels with Dicke superradiance in photon interactions.

The paper focuses on calculating superradiant interaction rates for various cosmic relics, including:

• Cosmic Neutrino Background (CνB): The authors demonstrate that the CνB can interact with a rate of O(Hz) when scattering off a 10 cm spin-polarized sphere, representing a substantial enhancement compared to incoherent inelastic contributions. They also investigate the possibility of detecting neutrino mass eigenstate transmutations during scattering, offering a unique CνB signature.
• Dark Matter: The paper examines both scattering and absorption of dark matter candidates. For scattering, they calculate upper bounds on interaction rates for fermionic and bosonic dark matter with spin-polarized targets. For absorption, they focus on axion-like particles, highlighting the similarities and differences with photon interactions and emphasizing the importance of coherence time.

The authors propose that superradiant interactions can manifest as detectable noise in quantum systems, offering observables sensitive to the total interaction rate rather than just the net energy exchange. This approach could lead to the development of ultra-low threshold detectors for weakly interacting particles.

The paper concludes by acknowledging limitations and suggesting future research directions, including developing concrete experimental protocols and exploring the impact of light mediators on interaction rates.

Stats

The CνB interacts with a rate of O(Hz) when scattering off a 10 cm liquid or solid-state density spin-polarized sphere.
This interaction represents a O(10^21) enhancement compared to the incoherent inelastic contribution.
For QCD axion dark matter, similar rates can be achieved with much smaller samples, N ∼O(10^15)(m/2×10^−8 eV)^−1/2, where m is the axion mass.
The local dark matter density is ρDM ≈0.3 GeV/cm3.
The velocity dispersion of virialized DM in the galaxy is v0 ≈235 km/s.

Quotes

"Superradiant interactions may provide a new avenue for detection by enhancing the interaction rate, as well as providing new observables associated with the excitation of the internal state of the system."
"These considerations point to new observables that go beyond traditional net energy exchange. These observables are sensitive to the sum of the excitation and de-excitation rates – instead of the net energy exchange rate which can be very suppressed – and can be viewed as introducing diffusion and decoherence to the system."
"While we postpone to upcoming work proposing a concrete protocol that extracts these effects from a macroscopic ensemble of atoms, the effects presented in this paper may point to a new class of ultra-low threshold detectors."

Key Insights Distilled From

Superradiant Interactions of the Cosmic Neutrino Background, Axions, Dark Matter, and Reactor Neutrinos

by Asimina Arva... at arxiv.org 11-06-2024

https://arxiv.org/pdf/2408.04021.pdf

Deeper Inquiries

What are the practical challenges in creating and maintaining the required quantum states (like the Dicke state) for macroscopic targets in a real-world experimental setup?

Creating and maintaining macroscopic quantum states like the Dicke state for superradiant interactions pose significant experimental hurdles. Here's a breakdown of the challenges:

Entanglement Generation: Dicke states require entangling a large number of particles. Achieving this high degree of entanglement over macroscopic scales is extremely difficult. Existing methods, like those used in quantum optics, struggle to scale up to the vast number of atoms needed for these detectors.
Decoherence: Macroscopic quantum states are incredibly fragile. Interactions with the environment, even at the quantum level (e.g., stray electromagnetic fields, thermal fluctuations), can easily destroy the delicate superposition and entanglement, leading to decoherence. This collapses the system into a classical state, eliminating the superradiant enhancement.
Maintaining Uniformity: The theoretical calculations often assume uniform density and perfect alignment of spins within the target material. In reality, achieving this level of uniformity is a major challenge. Imperfections and variations within the material can disrupt the coherence necessary for superradiant interactions.
Energy Splitting Control: Precisely controlling and maintaining the energy splitting (ω₀) of the two-level system is crucial. Fluctuations in magnetic fields or other environmental factors can shift ω₀, throwing off the delicate energy matching required for resonant interactions with low-energy particles like neutrinos.
Timescales: The coherence time of the prepared state needs to be long enough compared to the interaction time with the weakly interacting particles. For particles like CνB neutrinos, this demands exceptionally long coherence times, pushing the boundaries of what's currently achievable.
Overcoming these challenges demands significant advancements in quantum control techniques, material science, and experimental design.

Could the proposed detection method based on superradiant interactions be susceptible to background noise from other sources, and how could this noise be mitigated?

Yes, detectors based on superradiant interactions are inherently susceptible to various background noise sources, potentially mimicking or obscuring the faint signals of interest. Here are some key noise sources and mitigation strategies:

Thermal Noise: At finite temperatures, thermal fluctuations can excite the two-level systems, creating a background noise floor. Mitigation involves operating at extremely low temperatures (cryogenic environments) to suppress thermal excitations.
Electromagnetic Interference (EMI): Stray electromagnetic fields can couple to the spins, causing unwanted transitions and noise. Shielding the experiment from external EMI using Faraday cages and employing careful grounding and filtering techniques are essential.
Vibrations and Mechanical Noise: Physical vibrations can mechanically disturb the target material, introducing decoherence and noise. Using sophisticated vibration isolation systems and operating in seismically quiet environments can help minimize this noise.
Cosmic Rays and Natural Radioactivity: Cosmic rays and radioactive decay from materials in the detector and surroundings can produce background events that might be misidentified as signals. Placing the experiment deep underground to shield from cosmic rays and using materials with low intrinsic radioactivity can reduce this background.
Spontaneous Emission: Even in the absence of external stimuli, the two-level systems can spontaneously decay from the excited state, emitting radiation that contributes to noise. Choosing systems with long spontaneous emission lifetimes and optimizing the detector geometry to minimize the collection of this emitted radiation can help.
Discriminating the signal from these backgrounds will require a combination of strategies:

Energy and Momentum Matching: Carefully selecting the energy splitting (ω₀) to match the expected energy transfer from the particles of interest provides a primary filter.
Signal Timing and Correlation: Exploiting any known temporal characteristics of the signal, such as the coherence time of axion dark matter, can help distinguish it from random noise.
Directional Information: If possible, designing detectors that can provide directional information about the incoming particles can help differentiate signals from isotropic backgrounds.
Multiple Detector Vetoes: Employing an array of detectors and using coincidence techniques—where only events registered in multiple detectors are considered—can significantly reduce the impact of localized noise sources.

If successful, what other fundamental physics questions could be explored using detectors based on superradiant interactions?

The successful development of detectors based on superradiant interactions could open exciting avenues for exploring fundamental physics beyond the Standard Model. Here are some compelling possibilities:

Precision CνB Cosmology: Detecting the Cosmic Neutrino Background (CνB) and measuring its properties with high precision would provide a direct window into the early universe, offering insights into Big Bang nucleosynthesis, neutrino physics, and the processes that shaped the cosmos in its infancy.
Dark Matter Properties: Superradiant detectors could potentially probe the nature of dark matter in unprecedented ways. By tuning the energy splitting, these detectors might be able to identify different dark matter candidates, measure their masses, and study their interactions with ordinary matter, shedding light on this elusive component of the universe.
Neutrino Mass Hierarchy: The distinct energy signatures of neutrino up-conversion and down-conversion processes in superradiant interactions could provide a novel method for determining the neutrino mass hierarchy—a crucial unknown in neutrino physics.
Search for Sterile Neutrinos: The enhanced sensitivity of superradiant detectors might enable the search for hypothetical sterile neutrinos—particles that interact even more weakly than standard neutrinos. Their discovery would have profound implications for particle physics and cosmology.
Quantum Gravity Tests: Some theoretical models suggest that quantum gravitational effects might manifest as tiny violations of fundamental symmetries, such as Lorentz invariance. Superradiant detectors, with their extreme sensitivity to energy and momentum transfer, could potentially serve as platforms for testing these subtle violations and probing the interplay between gravity and quantum mechanics.
The development of superradiant detectors represents a challenging but potentially revolutionary frontier in experimental physics, promising to illuminate some of the most profound mysteries of the universe.