Fachrichtung Physik, Universität des Saarlandes, Campus E2.6, 666123, Saarbrücken, Germany.
Nat Commun. 2018 May 21;9(1):1998. doi: 10.1038/s41467-018-04341-2.
Entanglement between a stationary quantum system and a flying qubit is an essential ingredient of a quantum-repeater network. It has been demonstrated for trapped ions, trapped atoms, color centers in diamond, or quantum dots. These systems have transition wavelengths in the blue, red or near-infrared spectral regions, whereas long-range fiber-communication requires wavelengths in the low-loss, low-dispersion telecom regime. A proven tool to interconnect flying qubits at visible/NIR wavelengths to the telecom bands is quantum frequency conversion. Here we use an efficient polarization-preserving frequency converter connecting 854 nm to the telecom O-band at 1310 nm to demonstrate entanglement between a trapped Ca ion and the polarization state of a telecom photon with a high fidelity of 98.2 ± 0.2%. The unique combination of 99.75 ± 0.18% process fidelity in the polarization-state conversion, 26.5% external frequency conversion efficiency and only 11.4 photons/s conversion-induced unconditional background makes the converter a powerful ion-telecom quantum interface.
固定量子系统与飞行量子比特之间的纠缠是量子中继网络的基本要素。已经在囚禁离子、囚禁原子、金刚石中的色心或量子点中得到了证明。这些系统的跃迁波长在蓝色、红色或近红外光谱区域，而远程光纤通信需要在低损耗、低色散的电信波段中使用波长。一种将飞行量子比特在可见光/近红外波长与电信波段连接起来的成熟工具是量子频率转换。在这里，我们使用高效的偏振保持频率转换器将 854nm 连接到 1310nm 的电信 O 波段，以证明囚禁钙离子与电信光子的偏振态之间的纠缠具有 98.2 ± 0.2%的高保真度。偏振态转换的 99.75 ± 0.18%过程保真度、26.5%的外部频率转换效率和仅 11.4 个光子/s 的转换诱导无条件背景的独特组合使得该转换器成为强大的离子-电信量子接口。
