Quantum Metrology with Symmetric Dicke States Enables Enhanced Dark Matter Sensitivity

The search for wave-like dark matter receives a significant boost from new research identifying symmetric Dicke states as optimal tools for its detection, a finding that promises to enhance the sensitivity of current and future experiments. Ping He, Jing Shu from Peking University, and Bin Xu, alongside Jincheng Xu, demonstrate that these states maximise the information gained from short-baseline arrays of sensors, offering a robust advantage over other entangled states. The team’s work reveals that Dicke states maintain their collective sensitivity even in noisy environments, unlike more fragile alternatives, and they discover that incorporating a spatial-correlation phase further improves detection capabilities for closely spaced sensors. This framework, applicable to a range of stochastic bosonic fields including gravitational waves, paves the way for implementation using various quantum technologies such as superconducting qubits and atomic ensembles.

This work leverages the unique properties of these states to maximise the Fisher information, a measure of how precisely a quantity can be determined, for short-baseline arrays of sensors. The team implemented an ensemble-averaged metrological framework, accounting for the random phases and finite coherence inherent in the dark matter field, to enhance sensitivity. This framework allows for a robust enhancement of signal detection, scaling with the number of sensors used in the array.

The study demonstrates that Dicke states maintain a collective advantage even in the presence of amplitude-damping noise, a common source of signal degradation, while other entangled states, like GHZ states, rapidly lose sensitivity under similar conditions. For sensor separations comparable to the dark matter’s coherence length, the team discovered that incorporating an additional spatial-correlation phase into the optimal entangled state further improves performance, exceeding the capabilities of both Dicke and independent probes. This enhancement relies on precise control over the quantum state of the sensors and accurate measurement of the resulting signal. Researchers validated the feasibility of this approach by demonstrating that the required components, including the preparation of symmetric Dicke excitations and population-resolving measurements, are compatible with existing quantum technologies.

Specifically, the team highlights successful implementations using trapped ions, cold atoms, superconducting qubits, and nitrogen-vacancy centers, all of which naturally provide access to the necessary quantum states and measurement techniques. These advancements pave the way for realistic, noise-robust quantum-enhanced searches for wave-like dark matter and other spatially coherent fields with random phases, offering a promising new avenue for unraveling the mysteries of the universe. The framework developed applies broadly to the detection of stochastic bosonic fields, including gravitational waves, and is compatible with various quantum sensing platforms such as superconducting qubits, atomic ensembles, and nitrogen-vacancy centers. The authors acknowledge that their analysis focuses on specific noise models, namely phase and amplitude damping, and that a more comprehensive treatment of environmental noise may be necessary. They also note that the optimal performance relies on precise control of the spatial-correlation phase, which presents a practical challenge. Future work could explore strategies for mitigating these limitations and extending the framework to more complex noise environments, potentially leading to even more sensitive dark matter detectors.