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Chinese Physics Letters

Entanglement Manipulation for a Two-Mode Squeezed Vacuum State

Qingping Zhou, Mao-Fa Fang, Xiaojuan Liu, Xiaomei Chen, Qin Wu

Published Aug 4, 2004• 11 citations
Publisher

Abstract

By numerically analysing the entropy of entanglement of the output state from a Mach–Zehnder interferometer for the two-mode squeezed vacuum state input, it is found that if the internal phase shift of the interferometer is adjusted to the value of 0 or π, the entangling characteristic of the input state is efficiently preserved at the output. If the internal phase shift is tuned to the value of π/2, the two-mode squeezed vacuum state is completely disentangled at the output of the setup. If the internal phase shift deviates from the above values, the input state is degraded into a partially entangled output state. Based on these results, a method for optically realizing the entanglement preservation, entanglement degradation, and disentanglement via the interferometer is obtained.

DOI
10.1088/0256-307x/21/9/004

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By numerically analysing the entropy of entanglement of the output state from a Mach-Zehnder interferometer for the two-mode squeezed vacuum state input, it is found that if the internal phase shift of the interferometer is adjusted to the value of 0 or 7r, the entangling characteristic of the input state is efficiently preserved at the output. If the internal phase shift is tuned to the value of Tr/2, the two-mode squeezed vacuum state is completely disentangled at the output of the setup. If the internal phase shift deviates from the above values, the input state is degraded into a partially entangled output state. Based on these results, a method for optically realizing the entanglement preservation, entanglement degradation, and disentanglement via the interferometer is obtained.
We study a scheme for Mach–Zehnder (MZ) interferometer as a quantum linear device by injecting two-mode squeezed input states into two ports of interferometer. Two-mode squeezed states can be changed into two types of inputs for MZ interferometer: two squeezed states and Einstein–Podolsky–Rosen (EPR) entangled states. The interference patterns of the MZ interferometer vary periodically as the relative phase of the two arms of the interferometer is scanned, and are measured by the balanced homodyne detection system. Our experiments show that there are different interference patterns and periodicity of the output quantum states for two cases which depend on the relative phase of input optical fields. Since MZ interferometer can be used to realize some quantum operations, this work will have the important applications in quantum information and metrology.
We study the entanglement between the two beams exiting a Mach-Zehnder interferometer fed by a couple of squeezed-coherent states with arbitrary squeezing parameter. The quantum correlations at the output are functions of the internal phase shift of the interferometer, with the output state ranging from a totally disentangled state to a state whose degree of entanglement is an increasing function of the input squeezing parameter. A couple of squeezed vacuums at the input lead to maximum entangled state at the output. The fringe visibilities resulting from measuring the coincidence counting rate or the squared difference photocurrent are evaluated and compared to each other. Homodynelike detection turns out to be preferable in almost all situations, with the exception of the very-low-signal regime.
By analysing the action of a beamsplitter on squeezed vacuum states (SVSs), it is found that, if the two input light beams of the beamsplitter have the same squeezing amplitude and phase, the output state is a two-mode SVS. If the two input light beams of the beamsplitter have the same squeezing amplitude but a phase difference of π, the output state is a direct product state of two single-mode SVSs. Based on these results, we propose to distill a maximally entangled SVS from a partially entangled SVS by using a 50/50 beamsplitter and photodetectors.
By analysing the action of a beamsplitter on squeezed vacuum states(SVSs),it is found that,if the two input light beams of the beamsplitter have the same squeezing amplitude and phase,the output state is a two-mode SVS,If the two input light beams of the beamsplitter have the same squeezing amplitude but a phase difference of π,the output state is a direct porduct state of two single-mode SVS.Based on these results,we propose to distill a maximally entangled SVS from a partially entangled SVS by using a 50/50 beamsplitter and photodetectors.
We investigate the phase sensitivity of a Mach-Zehnder Interferometer (MZI) with an input of a non-Gaussian quantum entangled state, Two-Mode Photon-Subtracted Squeezed Vacuum states (TMPSSV). Parity detection is carried out at the output of the interferometer to obtain the phase uncertainty, which is a physical parameter that can quantify the sensitivity of interferometry. According to the simulation results, TMPSSV has a smaller phase uncertainty than the Two-Mode Squeezed Vacuum state (TMSV) in the entire range of the squeezing parameter which means the sensitivity of interferometry based on TMPSSV is higher than that of TMSV. Therefore, non-Gaussian entanglement based on TMPSSV provides a promising quantum resource for an ultra-sensitivity optical interferometer far beyond the standard quantum limit.