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arXiv:2610.12334

Quantum Co-Design of Inhomogeneous Many-Body Neutrino Fast Flavor Transformation

Zoha Laraib, Sherwood Richers, Alessandro Baroni, Kathleen Hamilton, In-Saeng Suh

quant-phastro-ph.HESubmitted Oct 8, 2026• Announced Oct 9, 2026• 0 citations
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Abstract

Dense-neutrino flavor evolution is a quantum many-body problem whose fully correlated treatment becomes rapidly more expensive with increasing particle number and spatial structure. We develop a \texttt{QCNO} quantum simulation code that maps a inhomogeneous forward-scattering neutrino Hamiltonian with advection and finite-range interactions to TEBD2 product-formula quantum circuits, and connects ideal many-body simulation, backend-aware execution, and fault-tolerant resource estimation within the same physical model. We reproduce the exact many-body evolution of the suppressed mean-field-like transverse fast flavor instability through $N=30$ and show that even a single open-boundary interaction generates Rënyi entanglement and non-stabilizer magic, although noisy backends still produce polarization RMSEs of order $0.1$--$0.3$. The restricted active interaction graph of this problem allows us to estimate the circuit depth and $T$ gate cost through $N=50$ for both NISQ and fault-tolerant approaches. The measured TEBD2 error in our fiducial ideal simulation of order $10^{-3}$ motivates a synthesis tolerance $\varepsilon_{\rm syn}\sim10^{-7}$, corresponding to about $70$ $T$ gates per $R_Z$ rotation. The generated circuit contains $1.4\times10^4$ $T$ gates per qubit for open boundaries (twice that for closed boundaries), requiring an application-level logical-$T$ error target of order $10^{-7}$ for early fault-tolerant architectures.

Comments
26 pages. 14 Figures. Applies to both the astrophysics and quantum computing field

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Dense-neutrino flavor evolution is a quantum many-body problem whose fully correlated treatment becomes rapidly more expensive with increasing particle number and spatial structure. We develop a \texttt{QCNO} quantum simulation code that maps a inhomogeneous forward-scattering neutrino Hamiltonian with advection and finite-range interactions to TEBD2 product-formula quantum circuits, and connects ideal many-body simulation, backend-aware execution, and fault-tolerant resource estimation within the same physical model. We reproduce the exact many-body evolution of the suppressed mean-field-like transverse fast flavor instability through N=30N=30N=30 and show that even a single open-boundary interaction generates Rënyi entanglement and non-stabilizer magic, although noisy backends still produce polarization RMSEs of order 0.10.10.1--0.30.30.3. The restricted active interaction graph of this problem allows us to estimate the circuit depth and TTT gate cost through N=50N=50N=50 for both NISQ and fault-tolerant approaches. The measured TEBD2 error in our fiducial ideal simulation of order 10−310^{-3}10−3 motivates a synthesis tolerance εsyn∼10−7\varepsilon_{\rm syn}\sim10^{-7}εsyn​∼10−7, corresponding to about 707070 TTT gates per RZR_ZRZ​ rotation. The generated circuit contains 1.4×1041.4\times10^41.4×104 TTT gates per qubit for open boundaries (twice that for closed boundaries), requiring an application-level logical-TTT error target of order 10−710^{-7}10−7 for early fault-tolerant architectures.
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