Noise suppression in a temporal-multimode quantum memory entangled with a photon via an asymmetrical photon-collection channel
Ya Li, Yafei Wen, Minjie Wang, Chao Liu, Hailong Liu, Shujing Li, Zhongxiao Xu, Hai Wang · Physical Review A · 2022
Quantum interfaces (QIs) that generate entanglement between a multimode atomic memory and a photon form a multiplexed repeater node and could greatly improve quantum repeater rates. Recently, a temporal multimode spin-wave memory entangled with a photon was demonstrated with cold atoms [Wen et al., Phys. Rev. A 100, 012342 (2019)]. However, due to the additional noise generated in a multimode operation, the fidelity of the spin-wave--photon entanglement significantly decreases with the mode number. So far, improvements in the temporal-multimode entanglement fidelity associated with suppressing the additional noise have not been explored. In this work, we propose and experimentally demonstrate a scheme that can suppress the additional noise of a temporally multiplexed QI. The scheme uses an asymmetric channel to retrieve the photons coming from the temporally multiplexed QI. For comparison purposes, we also set up a QI that uses a symmetric channel for photon collection. When the QIs store 14 modes, the measured Bell parameters $S$ for the QIs using the asymmetric and the symmetric photon-collection channels are 2.36 \ifmmode\pm\else\textpm\fi{} 0.03 and 2.24 \ifmmode\pm\else\textpm\fi{} 0.04, respectively, which means that a QI using an asymmetric channel provides a 3% increase in the entanglement fidelity, i.e., a 1.7-fold decrease in the additional noise, compared with a QI using a symmetric channel. In addition, the 14-mode entanglement QIs that use the asymmetric and symmetric collections preserve the violation of a Bell inequality for storage times of up to \ensuremath{\sim}25 and \ensuremath{\sim}20 \ensuremath{\mu}s, respectively, showing that the asymmetric QI has better entanglement storage performance.