CSU achieves long-time storage of multimode quantum states
Guo Guangcan's group has made new progress in the field of long-time spatial multimode quantum state storage: Shi Baoshen and Ding Dongsheng's group has realized the long-time storage of photonic high-dimensional orbital angular momentum states based on cold atomic system synthesis by using magnetic field manipulation technology combined with clock state preparation. The results were published in the journal Physical Review Letters on October 31 under the title "Long-Lived Memory for Orbital Angular Momentum Quantum States".
Quantum memory is the core of quantum relay, which is indispensable for long-range quantum communication. Because of the collective enhancement effect and spectral coherence, cold atomic systems can effectively store the quantum states of photons, and therefore are favored as a highly promising quantum memory medium. Numerous works in academia have shown that the layout of multimode memory into quantum networks can substantially increase the channel capacity, and thus the implementation of multimode quantum memory is of great value for building high-capacity quantum networks. Although important progress has been made in the field of multimode quantum storage, there are still many scientific problems that need to be solved for long-time spatial multimode storage based on cold atomic systems, one of which is the difficulty to guarantee the high fidelity of the stored multimode quantum states after long-time storage: this is caused by the fact that complex spatial modes are more susceptible to interference from the surrounding environment (e.g., magnetic field).
Fig. 1 Schematic diagram of operation. (a) sketch of the experimental setup; (b) schematic diagram of the energy level structure and principle of the symmetric clock state preparation; (c) energy level structure based on electromagnetically induced transparent storage.
The research team led by Baosen Shi and Dongsheng Ding has made important progress in the study of long-time storage of high-dimensional multimode photonic states using the rubidium cold atom system and based on the angular momentum degrees of freedom of photon orbitals. In the present work, the team further extends the storage time by manipulating the polarized magnetic field to suppress the transverse decoherence of spatial modes and by preparing magnetically insensitive states (as shown in Figure 1). The team used a thermal atomic cell with time-controlled reverse-pumped light as a narrow-band filter to achieve filtering and detection of single-photon scale signal light.
The work carried out a long-time storage study with two 3D orbital angular momentum superposition states (as shown in Figure 2), and the absolute fidelity was experimentally found to be much higher than the quantum-classical bound calculated from the pulse-averaged photon number and storage efficiency after a storage time of 400 μs, indicating that the memory can still work in the quantum domain. Meanwhile, the readout efficiency of the memory decays from 10.7% to 4.7% when the storage time is extended from 10 μs to 400 μs, a reduction of less than 60%. The research results have important reference significance for the construction of high-capacity quantum networks.
Fig. 2 Experimental results. (a) variation of fidelity, efficiency with storage time, and quantum-classical bounds, while also demonstrating the variation of the storage pattern with time through ICCD recording of the stored strongly coherent optical signal; (b) density matrix of the reconstructed readout signal.
The results were fully acknowledged by the reviewers: "...No doubt, this work contains valuable results that will have a profound impact on the design and implementation of quantum memories..." (" ...No doubt, the manuscript contains highly relevant results, with high impact on the development of quantum memory design and realization ...").
Yinghao Ye, a postdoctoral fellow at the Key Laboratory of Quantum Information, CAS, and Lei Zeng, a PhD student, are co-first authors of this paper; Dongsheng Ding and Baoshen Shi are co-corresponding authors. The results were supported by the Ministry of Science and Technology, the Foundation Committee, the Chinese Academy of Sciences, a major science and technology project in Anhui Province, and the University of Science and Technology of China.
Article Link：
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.193601
