摘要 : The ultimate achievable phase sensitivity in a Mach-Zehnder interferometer is given by the Heisenberg limit of 1/ N , with N being the number of photons in the interferometer. However, the best-known phase sensitivity as obtained ... 展开 The ultimate achievable phase sensitivity in a Mach-Zehnder interferometer is given by the Heisenberg limit of 1/ N , with N being the number of photons in the interferometer. However, the best-known phase sensitivity as obtained through intensity measurements is approximate to 2/ N . In this work, we provide examples of states that achieve improved phase sensitivity lesser than 2/ N , albeit greater than 1/ N . A modified scheme of the Mach-Zehnder interferometer that uses the first excited Fock state, single-mode squeezers, and an additional beam splitter is presented. It is shown that the modified scheme attains a phase sensitivity lesser than 2/ N , through intensity measurements. The effect of attenuation and noise on phase sensitivity is considered. Phase sensitivity superior to the standard quantum limit is seen to persist for a finite range of attenuation and noise. 收起