Residual coherence dominates entanglement in neutrino oscillation, study finds

Residual Coherence Outshines Entanglement in Neutrino Oscillations

A recent theoretical analysis by Dr. Donovan Lekhashri Konwar and collaborators at IIT Jodhpur and partner institutions shows that the residual l₁‑norm coherence of a neutrino flavor state remains a stronger indicator of quantum correlation than traditional entanglement measures such as Concurrence Fill and the three‑π entanglement. The work, posted on arXiv (https://arxiv.org/abs/2611.16709v1), extends the standard plane‑wave treatment of neutrino propagation by employing a wave‑packet formalism and incorporating constant matter density, using the DUNE experimental configuration as a realistic benchmark.

Wave‑Packet Formalism and Matter Effects

Neutrinos are produced and detected as localized wave packets rather than infinite plane waves. By assigning a finite spatial width σₓ to the packet, the authors capture decoherence that arises during long‑distance travel. Their calculations reveal that smaller σₓ (higher measurement precision) accelerates the damping of oscillatory features, smoothing the energy dependence of survival probabilities. Adding a constant matter potential further modifies both the amplitude and position of oscillation peaks, illustrating a non‑trivial interplay between decoherence and matter‑induced refraction.

Quantifying Quantum Correlations

Three correlation measures are evaluated for an initial muon‑flavor state:

1. Residual l₁‑norm coherence – a basis‑dependent coherence metric derived from the density matrix.
2. Concurrence Fill – an extension of two‑qubit concurrence to multipartite systems.
3. Three‑π entanglement – a multipartite entanglement monotone.

All three are expressed analytically in terms of transition probabilities P(νₐ→ν_γ). Across a range of wave‑packet widths and matter potentials, the residual coherence consistently retains larger values and shows weaker sensitivity to the CP‑violating phase, while the entanglement measures drop more rapidly as decoherence sets in.

Beyond the DUNE Baseline

The study pushes the analysis past DUNE’s nominal 1300 km baseline, exploring propagation distances up to several thousand kilometers. At sufficiently long distances, the three correlation measures converge to constant, baseline‑independent values, indicating that the quantum‑correlation signature becomes dominated by residual coherence regardless of the specific experimental configuration.

Implications

These findings suggest that, for realistic neutrino experiments, coherence‑based descriptors may provide a more robust handle on quantum‑correlation effects than entanglement‑based ones. This could influence the design of future long‑baseline neutrino facilities and the interpretation of precision oscillation data, especially when wave‑packet effects cannot be ignored.

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The authors acknowledge that their results rely on the chosen wave‑packet parameters and a simplified constant‑density matter model. Experimental validation will require dedicated studies of decoherence in actual neutrino beams.