Quantum geometric tensor determines the pure-state i.i.d. conversion rate in the resource theory of asymmetry for any compact Lie group

Quantifying physical concepts in terms of the ultimate performance of a given task has been central to theoretical progress, as illustrated by thermodynamic entropy and entanglement entropy, which respectively quantify irreversibility and quantum correlations. Symmetry breaking is equally universal, yet lacks such an operational quantification. While an operational characterization of symmetry breaking through asymptotic state-conversion efficiency is a central goal of the resource theory of asymmetry (RTA), such a characterization has so far been completed only for the $U(1)$ group among continuous symmetries. Here, we identify the complete measure of symmetry breaking for a general continuous symmetry described by any compact Lie group. Specifically, we show that the asymptotic conversion rate between many copies of pure states in RTA is determined by the quantum geometric tensor, thereby establishing it as the complete measure of symmetry breaking. As an immediate consequence of our conversion rate formula, we also resolve the Marvian-Spekkens conjecture on conditions for reversible conversion in RTA, which has remained unproven for over a decade. Leveraging the connection between symmetry breaking and the theory of quantum reference frames, we also systematically introduce a standardized reference state for frameness based on our asymptotic conversion theory. In addition, by applying our analysis to a standard quantum-thermodynamic scenario, we show that asymptotic state conversion in contact with heat baths generally requires macroscopic coherence in the thermodynamic limit.

💡 Research Summary

The paper tackles a long‑standing open problem in the resource theory of asymmetry (RTA): identifying a complete monotone that fully characterizes the asymptotic interconversion rate between many copies of pure quantum states when the symmetry group is a general compact Lie group. While such a characterization existed only for the abelian U(1) case, the authors prove that the quantum geometric tensor (QGT) – the matrix comprising the quantum Fisher information and the Berry curvature – serves as the unique, complete measure of symmetry breaking for any compact Lie group.

The central result (Theorem 1) states that for two pure states |ψ⟩ and |φ⟩, the optimal i.i.d. conversion rate R(ψ→φ) is given by the largest scalar λ such that the QGT of the source dominates λ times the QGT of the target in the Löwner order: \