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Quantum Sensing Radiative Decays of Neutrinos and Dark Matter Particles

This paper proposes using highly sensitive quantum devices, such as superconducting qubits and trapped ions, to detect the faint electromagnetic signals from radiative decays of cosmic neutrinos and dark matter, demonstrating that current technology can probe dark matter candidates while future scalable architectures are needed to exceed limits on neutrino magnetic moments.

Original authors: Zhongtian Dong, Doojin Kim, Kyoungchul Kong, Myeonghun Park, Miguel A. Soto Alcaraz

Published 2026-09-24

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CC0 1.0

Original authors: Zhongtian Dong, Doojin Kim, Kyoungchul Kong, Myeonghun Park, Miguel A. Soto Alcaraz

Original paper dedicated to the public domain under CC0 1.0 (http://creativecommons.org/publicdomain/zero/1.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The universe is filled with invisible things that shape everything we see, yet remain stubbornly out of reach. Among the most elusive are dark matter, the mysterious substance that holds galaxies together, and the cosmic neutrino background, a faint sea of ghostly particles left over from the Big Bang. For decades, scientists have tried to catch these particles, but they interact so weakly with ordinary matter that they pass through detectors like light through glass. Traditional methods rely on waiting for a rare collision, but when the signal is this faint, the wait can be endless. Recently, a new approach has emerged from the world of quantum technology, where scientists are learning to build devices sensitive enough to feel the tiniest whisper of energy. Instead of waiting for a crash, these new tools listen for a subtle shift, a tiny vibration caused by a particle decaying and releasing a single photon of light.

A team of physicists has now explored how these ultra-sensitive quantum devices could be used to detect the radiative decays of dark matter and cosmic neutrinos. They focused on two specific types of hardware: superconducting circuits that act like artificial atoms, and trapped ions, which are single atoms held in place by electric fields. The researchers imagined a scenario where a heavy, invisible particle slowly breaks apart into a lighter version of itself and a single photon. Even though this photon is incredibly faint, the team calculated that it would create a tiny, rhythmic electric field. If a quantum sensor is tuned to the exact frequency of this field, it could absorb the energy and jump from a calm, resting state to an excited one. By watching for these jumps, scientists could effectively count the decays of these invisible particles.

The study shows that this method is already powerful enough to test certain theories about dark matter. The researchers found that current quantum sensors, using existing technology, could probe the decay of dark matter candidates with masses around a few ten-thousandths of an electron volt. This is a region of physics that has been difficult to explore with other tools. The team also looked at the cosmic neutrino background, which is even harder to detect because the particles are lighter and the signals are weaker. Their analysis suggests that while today's devices are not quite sensitive enough to see these neutrino decays, the path forward is clear. If scientists can build larger systems with thousands of quantum sensors working together, and if they can keep these sensors stable for longer periods, they could eventually reach the sensitivity needed to detect the neutrino magnetic moment, a property that has never been measured directly.

To make this work, the researchers had to solve a tricky problem: how to describe a single photon that appears randomly from a decay, rather than a steady beam of light. In the quantum world, a single photon does not act like a continuous wave; it is a discrete packet of energy. However, the team demonstrated that for the purpose of calculating how a sensor reacts, they could treat the photon's effect as a smooth, oscillating electric field. This allowed them to use well-understood physics to predict how likely a sensor is to absorb the energy. They found that the probability of a sensor catching a signal grows rapidly if the sensor stays coherent, or stable, for a longer time. This means that improving the stability of these quantum devices is the key to unlocking new discoveries.

The team also investigated a way to make the sensors even more powerful by using a technique called entanglement. By linking multiple sensors together in a special quantum state, they showed that the collective response to a signal could be much stronger than the sum of individual sensors. This "collective enhancement" could allow a large array of sensors to detect a signal that would be invisible to a single device. While building such a large, entangled system is a significant engineering challenge, the researchers outlined a roadmap for how it might be achieved in the coming years. They noted that current experiments are already setting limits on what is possible, and their work provides a clear target for future improvements.

One of the most important findings of the paper is the distinction between what is possible now and what requires future technology. For dark matter, the results are encouraging: the decay of certain heavy dark matter particles could be within reach of devices that are already being built or tested. For the cosmic neutrino background, the situation is more demanding. The signals from neutrino decays are so faint that detecting them will require a massive leap in scale, potentially involving hundreds of thousands of sensors working in unison. The researchers also considered constraints from previous experiments, noting that their proposed method must respect the limits already set by other observations. They found that their approach does not contradict existing data but rather opens up new windows to look at the same phenomena.

The study concludes that quantum sensing represents a promising new frontier for particle physics. By treating the faint electric fields from particle decays as a signal that can be amplified and measured, scientists can move beyond the limitations of traditional detection. The work does not claim to have found dark matter or neutrinos yet; instead, it maps out the territory where these discoveries might happen. It suggests that with continued progress in making quantum devices more stable and scalable, we may soon be able to listen to the faintest echoes of the universe's earliest moments. The path forward involves refining these sensors, scaling them up, and waiting for the moment when the noise of the background falls away, leaving only the clear signal of a particle decaying in the dark.

Technical Summary: Quantum Sensing Radiative Decays of Neutrinos and Dark Matter Particles

Problem Statement
The paper addresses the challenge of detecting extremely weakly interacting particles, specifically the radiative decays of Dark Matter (DM) candidates and the Cosmic Neutrino Background (CνB). Traditional detection methods struggle with these signals due to their low interaction cross-sections and faint electromagnetic signatures. While quantum devices (such as superconducting transmon qubits and trapped ions) have been proposed for detecting bosonic DM (e.g., axions and hidden photons), their potential to detect radiative decays of fermionic or scalar particles into Standard Model photons remains largely unexplored. The authors aim to evaluate whether current and near-future quantum sensor architectures can probe these specific decay channels, particularly focusing on the transition from ground to excited states induced by decay photons.

Methodology
The authors develop a theoretical framework to model the interaction between decay photons and quantum sensors. Key methodological components include:

Effective Field Modeling: Instead of assuming decay photons form a coherent classical wave, the authors model the interaction using a response-level parametrization. They derive an effective electric field, $\vec{E}^{(\text{eff})}$ , induced by the decay photons. This field is treated as a near-resonant sinusoidal drive, justified by analyzing the field two-point correlation function ( $G^{(1)}$ ) rather than the one-point expectation value. This approach correctly captures the detector response for incoherent, single-photon events in the few-photon limit.
Sensor Platforms: The study evaluates two specific quantum platforms:
- Transmon Qubits: Modeled as anharmonic oscillators where the effective electric field modifies the Hamiltonian, inducing transitions between ground ( $|g\rangle$ ) and excited ( $|e\rangle$ ) states.
- Trapped Ions: Modeled as harmonic oscillators where the electromagnetic field couples to the ion's mechanical motion via the Coulomb interaction.
Measurement Protocol: The detection strategy involves a cyclic process of initialization, free evolution under the potential decay field, and readout. The authors calculate the transition probability ( $p^*$ ) within the coherence time ( $\tau$ ) and map this to a counting statistics problem. They account for background noise (dark counts) arising from readout errors and thermal excitation.
Signal Enhancement: The paper investigates the potential for collective enhancement using symmetric Dicke states. By preparing $n_q$ qubits in an entangled state, the transition probability can theoretically scale as $n_q^2$ (superabsorption), although the authors note practical challenges regarding amplitude damping and phase coherence for sporadic decay events.

Key Contributions

Theoretical Framework for Radiative Decays: The authors provide the first detailed mapping of radiative decay signals (from DM and CνB) to the response of quantum sensors, establishing the relationship between particle decay rates, number densities, and the effective electric field amplitude sensed by qubits.
Justification of Sinusoidal Approximation: A rigorous derivation is provided showing that modeling a single-photon decay event as a sinusoidal drive is valid for estimating transition probabilities, provided the analysis relies on the normally ordered field correlator ( $G^{(1)}$ ) rather than the field expectation value.
Parameter Space Mapping: The study translates theoretical decay rates into experimental observables, defining the accessible parameter space for DM mass ( $m_2$ ), mass splitting ( $\Delta m^2$ ), and coupling strengths ( $\mu$ ) for both transmon and trapped ion systems.

Results

Dark Matter Decay:
- The authors analyze a two-component DM scenario ( $X_2 \to X_1 + \gamma$ ).
- They demonstrate that current quantum technologies (specifically transmon qubits with existing coherence times and readout fidelities) can effectively probe radiative decays of DM candidates.
- By reinterpreting recent results from the DarQ collaboration (which searched for hidden dark photons), the authors derive exclusion limits on the DM mass ( $m_2 \gtrsim 4.15 \times 10^{-5}$ eV) and coupling parameter ( $\mu$ ) for specific resonance frequencies.
- For trapped ions, the analysis shows sensitivity to different mass ranges, with transition probabilities calculated for specific ion species (e.g., $^{171}\text{Yb}^+$ , $^{43}\text{Ca}^+$ ).
Cosmic Neutrino Background (CνB):
- The study evaluates the detection of neutrino radiative decays ( $\nu_i \to \nu_j + \gamma$ ) driven by transition magnetic moments ( $\mu_\nu$ ).
- Current Limitations: The authors find that current quantum devices lack the sensitivity to detect the CνB or probe neutrino magnetic moments beyond existing experimental bounds (e.g., $\mu < 10^{-11} \mu_B$ ).
- Future Requirements: Probing the CνB requires scalable quantum architectures with collective enhancement. The authors present a "futuristic" scenario utilizing $10^5$ qubits (motivated by IBM's roadmap) and Dicke state engineering. In this scenario, 5 $\sigma$ discovery significance becomes achievable for specific mass splittings ( $\Delta m^2 \sim 10^{-5}$ eV $^2$ ) in the 1–10 GHz range.
Dicke State Enhancement: While the paper outlines a quantum circuit for preparing symmetric Dicke states to achieve $n_q^2$ scaling, it explicitly cautions that practical implementation is challenging due to intrinsic noise and amplitude damping, and that the sporadic nature of decay events may hinder the maintenance of phase coherence required for such enhancement.

Significance and Claims
The paper claims that quantum sensors offer a novel and viable pathway for exploring radiative decays of Dark Matter, a regime previously inaccessible to traditional detectors. The authors assert that:

DM Detection is Feasible: Existing quantum technology can already probe radiative DM decays, with current experiments like DarQ already constraining specific parameter spaces.
CνB Detection is Conditional: Detecting the CνB or probing neutrino magnetic moments beyond current limits is not possible with single-qubit or small-scale devices. It strictly requires scalable quantum systems with collective enhancement (e.g., large-scale qubit arrays and Dicke states).
Methodological Validity: The use of an effective sinusoidal field to model incoherent decay photons is a robust approximation for calculating detector response, bridging the gap between quantum optics formalism and phenomenological sensor modeling.

The authors conclude that while practical implementation faces significant hardware challenges (coherence times, noise, scalability), continued progress in quantum hardware could soon make these detection strategies experimentally realizable, opening a new frontier for fundamental physics.

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