Fig. 2: SMSS performance.

Performance (a, b) versus squeezing gain G with N_T = 10⁻² fixed; c, d versus thermal background photon number N_T with G = 40 dB fixed. a, c Advantage (in dB unit) of T-optimized quantum Fisher information rate \({{\mathcal{R}}}^{\star }\equiv \mathop{\max }\limits_{T}{\mathcal{J}}(T)/T\) over vacuum state input; b, d optimal waiting time T^⋆ normalized by axion coherence time τ_A (in log10 scale). Solid lines: T numerically optimized; Dot-dashed lines: asymptotic prediction with \(T=2\sqrt{2{N}_{{\rm{T}}}}{\tau }_{A}/\Gamma {\tau }_{A}G\). Purple dashed lines: asymptotic prediction of linear advantage Eq. (9) assuming non-saturated strong squeezing G_SAT ≫ G ≫ G_TH, N_T ≪ 1, Γτ_A ≪ 1. In subplot (a, b) we mark G_TH (≃20 dB here) and G_SAT (≃55 dB here) by right-pointing triangle and left-pointing triangle respectively. Gray dashed lines: 0dB advantage and G-saturated advantage Eq. (10). Cavity parameters: Γτ_A = 10⁻⁸.