Quantum Magic Reveals CP Phases Invisible to Entanglement in Spin-0 Decays

TL;DR

This paper demonstrates that standard quantum information measures are insensitive to CP phases in spin-0 decays, but stabilizer magic reveals these phases and offers practical CP detection methods.

Contribution

It introduces stabilizer magic as a new tool to detect CP phases in spin-0 decays, overcoming limitations of traditional entanglement measures.

Findings

Stabilizer Rénnyi entropy peaks at maximal non-Clifford mixing.

Magic-inspired CP witnesses are more efficient than previous methods.

Discovery-level sensitivity achieved at HL-LHC for H→τ+τ− decays.

Abstract

All standard scalar quantum-information measures -- concurrence, negativity, entanglement entropy, the optimized CHSH bound, and quantum Fisher information -- are CP-blind in ideal \\ spin-0 $\to f\bar f$ decays because the two-qubit spin state is maximally entangled for every CP angle. We show that stabilizer magic, fixed in the physical Pauli frame of spin analysis, escapes this blind spot: the stabilizer R\'enyi entropy admits an exact closed form, vanishing at CP-definite and Clifford phases and peaking at maximal non-Clifford mixing. Two experimentally accessible, magic-inspired CP witnesses follow; the linear amplitude is $14.3\times$ more efficient than its quartic counterpart and reaches discovery-level sensitivity at the HL-LHC for $H\to\tau^+\tau^-$.