The quantum Rabi model (QRM) is a fundamental model for light-matter interactions; the finite-component quantum phase transition (QPT) in the QRM has established a paradigmatic application for critical quantum metrology (CQM). However, this paradigmatic application is restricted to a local regime of the QPT which has only a single critical point. In this work we propose a globalized CQM in the QRM by introducing an auxiliary nonlinear term which is realizable and can extend the critical point to a continuous critical regime. As a consequence, high measurement precision is globally available over the entire coupling regime from the original critical point of the QRM down to the weak-coupling limit, as demonstrated by the globally accessible diverging quantum Fisher information in the dynamics. We illustrate a measurement scheme using quadrature dynamics, with globally criticality-enhanced inverted variance as well as the scaling relation with respect to finite frequencies. In particular, we find that the globally high measurement precision still survives in the presence of decoherence. Our proposal paves the way to break the local limitation of the QPT of the QRM in CQM and enables a broader application, with implications for applicability in realistic situations.

Close

PrevNext

View figure in article

• Light-matter interaction
• Quantum metrology
• Quantum phase transitions