Cui Liang, Su Jie, Li Xiaoying, Ou Z Y
College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Key Laboratory of Optoelectronics Information Technology of Ministry of Education, Tianjin, 300072, China.
Department of Physics, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana, 46202, USA.
Sci Rep. 2017 Nov 2;7(1):14954. doi: 10.1038/s41598-017-14955-z.
Few-mode fibers (FMFs) have been recently employed in classical optical communication to increase the data transmission capacity. Here we explore the capability of employing FMF for long distance quantum communication. We experimentally distribute photon pairs in the forms of time-bin and polarization entanglement over a 1-km-long FMF. We find the time-bin entangled photon pairs maintain their high degree of entanglement, no matter what type of spatial modes they are distributed in. For the polarization entangled photon pairs, however, the degree of entanglement is maintained when photon pairs are distributed in LP mode but significantly declines when photon pairs are distributed in LP mode due to a mode coupling effect in LP mode group. We propose and test a remedy to recover the high degree of entanglement. Our study shows, when FMFs are employed as quantum channels, selection of spatial channels and degrees of freedom of entanglement should be carefully considered.
少模光纤（FMF）最近已被应用于经典光通信中，以提高数据传输容量。在此，我们探索将少模光纤用于长距离量子通信的能力。我们通过实验在1公里长的少模光纤上以时间-bin和偏振纠缠的形式分发光子对。我们发现，无论时间-bin纠缠光子对分布在何种空间模式中，它们都能保持高度纠缠。然而，对于偏振纠缠光子对，当光子对以LP 模式分布时，纠缠度得以保持，但当光子对以LP 模式分布时，由于LP 模式组中的模式耦合效应，纠缠度会显著下降。我们提出并测试了一种恢复高度纠缠的补救方法。我们的研究表明，当将少模光纤用作量子通道时，应仔细考虑空间通道的选择和纠缠自由度。
