[论文解读] Multiphoton processes due to XPM nonlinearities in EIT systems:a basic description

Archana Sharma|arXiv (Cornell University)|Sep 5, 2011

Quantum and electron transport phenomena被引用 1

一句话总结

本文在电磁诱导透明（EIT）系统中的交叉相位调制（XPM）里发现了一种新颖的对称性，该对称性使得单个多光子过程可在多个光场中显现，从而产生强关联的时域纠缠光子以及跨场噪声相关性。论文推测存在两种非对称多光子过程，但仅证明其中一种在物理上可行，并揭示了一种此前未被解释的χ⁽⁵⁾吸收共振，其虚部表现出反常行为并可诱导压缩——这与已知的压缩机制截然不同。

ABSTRACT

We have found a novel symmetry for XPM(Cross Phase Modulation) systems .We prove that this symmetry is a necessary condition for a single multiphoton process to be visible in more than one field.We have found, two EIT(Electromagnetically Induced Transparency) systems that show cases of this symmetry.The above process has the possibility of leading to strong sources of temporally entangled photons of different frequency. For cases that do not show this symmetry,more than one species of multiphoton processes can take place and each one is visible in one field only. When there is a symmetry, we predict cross field noise correlations for the scattered fields.Cross field noise correlations have recently been seen in a different situation that can provide interesting variation to our study,namely the generated fields in FWM(Four Wave Mixing). We postulate or conjecture the existence of two types of asymmetric multiphoton processes.We show only one of these is possible. One of systems we use for this purpose generates a $\chi^{(9)}$ absorption resonance that is observable on the same trace that shows linear features, in an experiment described in a previous work but the order of nonlinearity newly interpreted using this work.This high order nonlinearity should be very sensitive to cross field correlations.We show how it can be used to test our conjecture of asymmetric processes. We also come across an important $\chi^{(5)}$ absorption,comparable to linear absorption, that is anomalous.The anomaly is that the Imaginary part of this XPM nonlinearity can cause squeezing.We give a qualitative argument which shows that we don't expect the Imaginary part of the XPM nonlinearities we usually come across, to cause squeezing.This promising source of squeezing, is qualitatively different from the other sources hitherto known.

研究动机与目标

• 识别XPM系统中一种新对称性，以实现多光子过程在多个光场中的可见性。
• 研究基于EIT的XPM系统中跨场噪声相关性出现的条件。
• 探索非线性光学系统中非对称多光子过程的存在性与可行性。
• 以高阶非线性与交叉相关性重新解释先前观测到的χ⁽⁹⁾吸收共振。
• 分析χ⁽⁵⁾非线性中虚部异常行为的机制，其可能诱导量子压缩。

提出的方法

• 对EIT系统中的XPM非线性进行理论分析，推导出多光子过程在多个光场中可见的必要对称性条件。
• 采用两种特定的EIT系统，验证该对称性及其对多光子过程与噪声相关性的影响。
• 应用非线性响应理论，从实验数据中识别并表征高阶非线性极化率，包括χ⁽⁹⁾与χ⁽⁵⁾。
• 通过定性论证表明，XPM非线性中虚部通常不会引起压缩，但χ⁽⁵⁾的异常情况例外。
• 利用新提出的对称性框架重新解释先前实验中观测到的χ⁽⁹⁾共振。
• 将所提出的χ⁽⁵⁾机制与已知的压缩源进行比较，突出其在定性上的独特性。

实验结果

研究问题

• RQ1 在XPM系统中，单个多光子过程在多个光场中可见的必要对称性条件是什么？
• RQ2 由于该对称性，EIT系统中是否可能出现跨场噪声相关性？其与多光子过程有何关联？
• RQ3 是否存在两种类型的非对称多光子过程？如果是，哪一种在物理上是可实现的？
• RQ4 先前观测到的χ⁽⁹⁾吸收共振如何通过高阶非线性与交叉相关性重新解释？
• RQ5 为何χ⁽⁵⁾ XPM非线性中虚部的表现与通常预期相反，反而能诱导压缩？

主要发现

• 识别出XPM系统中一种新对称性，该对称性是单个多光子过程在多个光场中可见的必要条件。
• 该对称性可实现不同频率的强时域纠缠光子的生成。
• 预测在对称XPM系统中将出现跨场噪声相关性，与最近在四波混频（FWM）过程中的观测结果一致。
• 基于理论框架，仅两种推测的非对称多光子过程中的一种在物理上可行。
• 发现χ⁽⁵⁾吸收共振具有异常特性，其虚部可诱导量子压缩——这与已知机制截然不同。
• 先前实验中观测到的χ⁽⁹⁾吸收共振被重新解释为高阶非线性的特征，对跨场相关性敏感。