Entanglement-Enhanced Quantum Metrology via Alternating In-Phase and Quadrature Modulation

Quantum metrology harnesses quantum entanglement to improve measurement precision beyond the standard quantum limit. Although nonlinear interaction is essential for generating entanglement, during signal accumulation, it becomes detrimental and therefore must be suppressed. To address this challenge, we propose an alternating in-phase and quadrature modulation (AIQM) scheme, designed to operate under a fixed nonlinear interaction. During signal accumulation, our time-interleaved approach sequentially applies the in-phase and quadrature driving fields, thereby eliminating the effects of nonlinear interaction. Our AIQM scheme achieves better metrological performance than conventional schemes, particularly under strong nonlinear interaction and prolonged signal accumulation, with pronounced robustness against parameter variations. Furthermore, we propose a full-stage AIQM protocol in which the one-axis twisting interaction remains fixed throughout the procedure. This protocol exhibits significantly better metrological performance than the protocol without AIQM, and demonstrates strong robustness against detection noise. By selectively eliminating and utilizing nonlinear interactions via AIQM, our work enables high-precision and high-accuracy entanglement-enhanced measurement without requiring active control of the nonlinear interaction for realistic quantum sensing and many-body metrology.