Chuang You-Lin, Lee Ray-Kuang, Yu Ite A
Opt Express. 2021 Feb 1;29(3):3928-3942. doi: 10.1364/OE.413217.
Quantum entanglement is an essential ingredient for the absolute security of quantum communication. Generation of continuous-variable entanglement or two-mode squeezing between light fields based on the effect of electromagnetically induced transparency (EIT) has been systematically investigated in this work. Here, we propose a new scheme to enhance the degree of entanglement between probe and coupling fields of coherent-state light by introducing a two-photon detuning in the EIT system. This proposed scheme is more efficient than the conventional one, utilizing the ground-state relaxation (population decay or dephasing) rate to produce entanglement or two-mode squeezing which adds far more excess fluctuation or noise to the system. In addition, maximum degree of entanglement at a given optical depth can be achieved with a wide range of the coupling Rabi frequency and the two-photon detuning, showing our scheme is robust and flexible. It is also interesting to note that while EIT is the effect in the perturbation limit, i.e. the probe field being much weaker than the coupling field and treated as a perturbation, there exists an optimum ratio of the probe to coupling intensities to achieve the maximum entanglement. Our proposed scheme can advance the continuous-variable-based quantum technology and may lead to applications in quantum communication utilizing squeezed light.
量子纠缠是量子通信绝对安全的关键要素。本文系统地研究了基于电磁诱导透明（EIT）效应在光场之间产生连续变量纠缠或双模压缩。在此，我们提出了一种新方案，通过在EIT系统中引入双光子失谐来提高相干态光的探测场与耦合场之间的纠缠程度。该方案比传统方案更有效，传统方案利用基态弛豫（粒子数衰减或退相）速率来产生纠缠或双模压缩，这会给系统增加更多的过量涨落或噪声。此外，在给定光学深度下，通过宽范围的耦合拉比频率和双光子失谐可以实现最大纠缠度，这表明我们的方案具有鲁棒性和灵活性。值得注意的是，虽然EIT是微扰极限下的效应，即探测场远弱于耦合场并被视为微扰，但存在一个探测强度与耦合强度的最佳比值以实现最大纠缠。我们提出的方案可以推动基于连续变量的量子技术发展，并可能导致在利用压缩光的量子通信中的应用。
