Fig. 3
Experimental description of Fisher information. Hong-Ou-Mandel interference of frequency entanglement with detunings of a 1.75 THz and (c) 5.34 THz, where the insets show the relative path delay predicted from normalized coincidence probability (for simplicity, only estimation results of blue data points are shown). These parameters enable us to calculate Fisher information in experiments for frequency entanglement with detunings of b 1.75 THz and d 5.34 THz (γ = 0.4 and α = 0.9), where the insets show their theoretical simulation in ideal case (γ = 0 and α = 1), and the red lines represent the ultimate limits of achievable Fisher information calculated from Cramér-Rao bound. The shaded regions bounded by two smoothed curves represent the standard deviation of experimental results estimated by statistical methods assuming a Poisson distribution
