Optimal Estimation in Weak Value Amplification with a Position Pointer

Abstract

We experimentally evaluate five estimators for weak-value amplification (WVA) using a position pointer to measure birefringence time delays. Two general approaches are considered: measuring the position shift $Δx$ and measuring the probability change $ΔP_w$ of successful postselection. Specifically, five estimators are investigated: CCD-detected fringe shift $Δx$, quadrant photodiode (PDQ) transversal voltage difference (XDIFF), and lock-in amplifier output phase $η$ (for $Δx$ measurement), as well as PDQ total output voltage (SUM) and CCD-detected average photon number $N_r$ (for $ΔP_w$ measurement). The measurement precision is characterized by the Allan deviation over a range of input laser powers $P_0$. Generally, measuring the position shift $Δx$ yields higher precision than measuring the probability change $ΔP_w$. At $P_0=0.5$~mW, corresponding to a laser-power-limited regime, direct measurement of the fringe displacement with the CCD achieves a minimum Allan deviation of $(5.30\pm0.10)\times10^{-3}$~as, approaching the corresponding photon-statistical Cramér--Rao bound (CRB). At $P_0=50$~mW, corresponding to a detector-limited regime, PDQ detection combined with lock-in demodulation provides the best precision, reaching $(1.80\pm0.06)\times10^{-3}$~as and remaining close to the corresponding CRB. These results demonstrate that the optimal readout depends on the available optical power, detector dynamic range, and technical noise, providing practical guidance for selecting readout strategies in high-precision WVA-based metrology.