Shulou(Shulou.com)11/24 Report--

Thanks to CTOnews.com netizen MissBook for the clue delivery! CTOnews.com, November 8, according to the official website of the University of Science and Technology of China, the academician team of the university of science and technology of China has made new progress in the storage of multi-modulus substates in long-time space: the research team of this team, Shi Baosen and Ding Dongsheng, have realized the long-term storage of photon high-dimensional orbital angular momentum states based on cold atomic ensemble by using magnetic field manipulation technology combined with clock state preparation method.

The realization of long-distance quantum communication is inseparable from quantum relay, in which quantum memory is the core of quantum relay construction. Cold atom ensemble is favored as a potential quantum memory medium because of its collective enhancement effect and spectral consistency, which can effectively store the quantum states of photons. A lot of academic work shows that the layout of multimode memory into quantum network can greatly improve the channel capacity, so the implementation of multimode quantum memory is of great value for the construction of high-capacity quantum network. Although important progress has been made in the field of multimode quantum storage, there are still many scientific problems to be solved in long-time spatial multimode storage based on cold atomic ensemble. One of them is that it is difficult to ensure that the stored multimode states still have high fidelity after long-term storage: this is due to the fact that complex spatial modes are more vulnerable to interference from the surrounding environment (such as magnetic field).

Fig. 1 working schematic diagram. (a) the schematic diagram of the experimental device; (b) the energy level structure and principle diagram of symmetrical clock state preparation; (c) the energy level structure based on electromagnetically induced transparency. Using rubidium cold atomic system and based on the degree of freedom of photon orbital angular momentum, the scientific research team led by Sposen and Ding Dongsheng have carried out the study of long-term storage of high-dimensional multimode photon states and made important progress. In this work, the team suppresses the lateral decoherence of the spatial mode by manipulating the polarized magnetic field, and further extends the storage time by preparing magnetic insensitive states (as shown in figure 1). The team uses the thermal atom cell with timing control reverse pump light as a narrow-band filter to filter and detect single-photon signal light.

This work takes the superposition states of two three-dimensional orbital angular momentum (shown in figure 2) as an example to carry out a long-time storage study. it is found that the absolute fidelity after 400 μ s storage time is much higher than the quantum-classical boundary calculated by the pulse average photon number and storage efficiency, indicating that the memory can still work in the quantum field. At the same time, when the storage time is extended from 10 μ s to 400 μ s, the readout efficiency of the memory decreases from 10.7% to 4.7%, which is reduced by less than 60%. The research results have important reference significance for the construction of high-capacity quantum networks.

Fig. 2 results of the experiment. (a) the change of fidelity and efficiency with storage time and the quantum-classical boundary, and the change of storage mode with time is also shown by recording the stored strongly coherent optical signal by ICCD; (b) the density matrix of the reconstructed readout signal. CTOnews.com learned that the relevant results were published in the academic journal Physical Review Letters under the title "Long-Lived Memory for Orbital Angular Momentum Quantum States" on October 31.

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