Asymmetry-enhanced phase sensing via asymmetric entangled coherent states

We study quantum phase sensing with asymmetric two-mode entangled coherent states (ECSs) in which the two local amplitudes take different values. We find the asymmetry-enhanced phase-sensing phenomenon in which the phase-sensing sensitivity is enhanced with increasing the asymmetry in the ECSs. We indicate that the phase-sensing sensitivity can attain and even surpass the Heisenberg limit in certain regimes of parameters. We further study the effect of decoherence induced by photon loss on the phase-sensing sensitivity. It is shown that the asymmetric ECSs have greater capability against decoherence compared with the symmetric ECSs. It is indicated that the asymmetric ECSs have significant advantages over the symmetric ECSs in quantum phase sensing. We also study the practical phase-sensing scheme with the intensity-difference measurement and show that the asymmetry in the asymmetric ECSs can enhance the phase sensitivity in the practical phase-measurement scheme. Our work reveals the asymmetry in the asymmetric ECSs is a resource for quantum-enhanced sensing and may be applied to ultrasensitive quantum phase sensing in the presence of photon loss.