Generation of indistinguishable single photons from resonantly driven semiconductor quantum dots by quantum frequency conversion to the telecom c-band

该研究项目的目标是在电信C波段（1550 nm）产生不可分辨的单光子，并演示利用这些单光子的光子量子门。电信光子的产生是使用混合方法完成的：起始点是嵌入在平面波导结构中的自组织InGaAs量子点，在光激发时在近红外（900 nm）发射单光子。我们计划使用双激子的共振、相干双光子π脉冲激发来激发量子点，从而导致连续发射的光子的高度不可逆性。在下一步中，我们通过非线性光学差频产生将900 nm处的单光子转换为1550 nm的波长。如最近在申请人的共同努力中所证明的，原始光场的非经典性质在转换过程期间被保留，因此被适当地描述为量子频率转换。这里重要的新目标是测试同一个量子点连续发射的光子的不可逆性是否也在转换过程中保持。这些实验的基本要求一方面是可再现地制造嵌入波导结构中的高质量InGaAs量子点（由斯图加特大学的Institut für Halbleiteroptik und Funktionelle Grenzflächen），另一方面是开发具有高效率和大噪声抑制的便携式频率转换装置（由Saarlandes大学的AG Quantenoptik）。该项目的主要目标是将来自两个空间遥远的共振激发InGaAs量子点的单光子量子频率转换为电信C波段内的共同波长，并演示电信光子的双光子干涉。量子点发射波长的微小变化，自然是由其几何尺寸的微小变化引起的，通过频率转换到共同的目标波长而被消除。在最后一步中，我们证明了不可区分的单个电信光子的适用性，通过使用光纤组件实现量子门（CNOT门）。后者的实验由两个申请人的小组联合进行。在电信波段确定性产生不可区分光子的计划实验对未来量子信息平台的可扩展性特别感兴趣。

The goal of the research project is the generation of indistinguishable single photons in the telecom C band (1550 nm) and the demonstration of a photonic quantum gate which makes use of these single photons. The generation of telecom photons is accomplished using a hybrid approach: starting point are self-organized InGaAs quantum dots embedded in planar waveguide structures emitting single photons in the near infrared (900 nm) upon optical excitation. We plan to excite the quantum dots using resonant, coherent two-photon pi-pulse excitation of the bi-exciton leading to a high degree of indistinguishability of the successively emitted photons. In a next step we convert the single photons at 900 nm via non-linear optical difference frequency generation to a wavelength of 1550 nm. As recently demonstrated in a joint effort of the applicants, the non-classical properties of the original light field are preserved during the conversion process, thus properly described as quantum frequency conversion. The important and new goal here is to test whether the indistinguishability of successively emitted photons of one and the same quantum dot is also preserved in the conversion process. Basic requirements for these experiments on one hand are reproducible fabrication of high quality InGaAs quantum dots embedded in waveguiding structures (by Institut für Halbleiteroptik und Funktionelle Grenzflächen, Universität Stuttgart) and development of portable frequency conversion setups with high efficiency and large noise suppression (by AG Quantenoptik, Universität des Saarlandes) on the other hand. Main goal of the project is quantum frequency conversion of single photons from two spatially remote, resonantly excited InGaAs quantum dots to a common wavelength within the telecom C band and demonstration of two-photon interference of the telecom photons. The small variations of the quantum dots´ emission wavelengths, naturally resulting from small variations of their geometric dimensions, are erased by frequency conversion to a common target wavelength. In a last step we demonstrate the applicability of the indistinguishable single telecom photons by implementing a quantum gate (CNOT gate) using fiber-optic components. The latter experiments are performed jointly by the two applicants´ groups. The planned experiments on deterministic generation of indistinguishable photons in the telecom band are of particular interest for scalability of future quantum information platforms.