Prefect Protection of Quantum-Enhanced Metrology from Dephasing Noise

One of the main obstacles for quantum-enhanced metrology is that the estimation accuracy enhanced by non-classical states is likely to be obliterated by noises. Here, we consider a scenario of phase estimation suffering from pure dephasing noise which is taken into account after the phase parameter being imprinted, and propose a scheme to effectively protect the quantum enhancement from both correlated and uncorrelated dephasing sources by performing a rotation operation prior to the noise. By invoking the Fisher information approach, we strictly prove that a $\pi /2$ rotation is the ideal one which can completely resist the influence of the phase noise for all real symmetric pure states and the optimal measurement approaching the ultimate sensitivity set by quantum Cramér–Rao bound is presented. Additionally, we numerically study the availability of the scheme with arbitrary angle rotation for different probe states and show that our scheme will still robust for general symmetric pure states even with non-ideal rotation operation. (paper)