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Acta Physica Sinica

Amplification of entangled beam based on four-wave mixing process

Xiaoyin Xu, Shengshuai Liu, Jietai Jing

Published Jan 1, 2022• 1 citation
Publisher

Abstract

Two-mode entangled state is an important quantum resource for quantum information. In this paper, the amplification of a single mode of two-mode entangled state (single-mode amplification scheme) and two modes of two-mode entangled state (two-mode amplification scheme) are theoretically proposed. Here, the optical beam splitter model is used to simulate the vacuum noise introduced by the loss in the optical transmission process. By utilizing the positivity under partial transpose criterion, we analyze the effect of the gain of the four-wave mixing process on the entanglement degree of the initial two-mode entangled state in two different amplification schemes. In these two schemes, we set the gain of the initial two-mode entangled state generation process to be 1.5, 2.5 and 50.0 respectively, and then change the gain of the amplification process in a certain range. We also set the transmission efficiency of the amplified beams for each of the two schemes to be a definite value. The results show that the entanglement of the initial two-mode entangled state decreases with the gain increasing under the condition of specific transmission loss in two schemes. When the gain does not exceed a certain value, the entanglement of the initial two-mode entangled state can be maintained. Then, with the increase of the gain, the entanglement of the initial two-mode entangled state will disappear. Moreover, the entanglement of the initial two-mode entangled state of the two-mode amplification scheme disappears faster than that of the single-mode amplification scheme. Our theoretical results pave the way for the experimental realization of the amplification of two-mode entangled state based on four-wave mixing process.

DOI
10.7498/aps.71.20211324

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Quantum vacuum noise is very detrimental for photon propagation and optical quantum memory, which particularly occurs in optically thick atomic media working under the condition of electromagnetically induced transparency (EIT) accompanied by a process of four-wave mixing (FWM). The suppression of quantum vacuum noise becomes now an imperative task for advancing the research and application of quantum memory. Here we present a scheme to suppress quantum vacuum noise and hence to improve the fidelity of photon propagation, by assuming that signal and idler laser fields are initially prepared in a two-mode squeezed vacuum state. With such a scheme, we show that the normal gain mode inherent in the EIT-based FWM system, which contributes optical gain to both the signal and idler fields, can be largely inhibited, giving rise to a significant suppression of the quantum vacuum noise along with their amplification and hence a large enhancement of the fidelity for photon propagation. The results reported here may have promising applications for high-fidelity quantum information processing and transformation, especially for improving the quality of multimode optical quantum memory based on EIT techniques.
Abstract We demonstrate the influence of dressed states on two-mode optical entanglement in a double Λ-type energy level atomic ensemble of parametric amplification four-wave mixing (PA-FWM) processes. By injecting a coherent or Einstein–Podolsky–Rosen field into PA-FWM channels, we investigate the corresponding entanglement. The quantum entanglement may be enhanced or suppressed via a bright state or a dark state. In free space, the two-mode entanglement is determined by nonlinear gain, which can be manipulated by field dressing in an atomic ensemble (i.e. Autler–Towns splitting, dressed enhancement/suppression of entanglement). However, in a ring cavity, the cavity dressing brings about the AT-like splitting of entanglement. Such an entanglement profile may be modified by field dressing through vacuum Rabi splitting, vacuum-induced enhancement and suppression of entanglement.