Recently, the Key Laboratory of Quantum Information of the Chinese Academy of Sciences led by Guo Guangcan, an academician of the Chinese Academy of Sciences at the University of Science and Technology of China, has made new progress in the direction of high-dimensional quantum relay research. The Shi Pusen group of the laboratory has realized the quantum of quantum entanglement of photon orbital angular momentum for the first time in the world. Storage further proves the feasibility of using high-dimensional quantum repeaters to realize long-distance large-quantity quantum information transmission. The results of this study were published in the February 4th Physical Review Letters.
The orbital angular momentum of a photon originates from the helical phase of the electromagnetic wave. The most common light with orbital angular momentum is Laguerre-Gaussian mode light. The wave front of this light is a helicoid. Around the central singularity, the phase of light is increasing. At the same time, the light intensity also has a special spatial distribution. Different orbital angular momentum corresponds to different spatial distribution of light intensity. A complete Hilbert space that forms an infinite dimension. Encoding photons in the orbital angular momentum space can greatly increase the photon information carrying capacity.
In addition, the use of high-dimensional photons of photons can also improve the security of quantum key transmission, realizing quantum information protocols such as quantum holographic teleportation, quantum mirror dense coding, holographic quantum computation, and can also be applied to the basic problems of quantum mechanics. the study. The implementation of long-distance quantum communication must rely on a series of quantum repeaters, where the quantum memory unit is the core of the quantum repeater. By establishing quantum entanglement between adjacent memory cells, quantum relaying technology can be used to realize quantum relays, thereby extending the distance of information transmission.
Therefore, the key problem that must be solved in realizing quantum information transmission with large information and long distance is the storage of quantum high-dimensional entanglement. Although people have successfully implemented single-photon storage with orbital angular momentum information, the research on the orbital angular momentum entanglement storage is still a blank and is a hot research field in the field of quantum information.
In recent years, Prof. Shi Baosen and doctoral student Ding Dongsheng have been working on carrying research on the storage of orbital angular momentum photons. Following the storage of single-photon pulses with orbital angular momentum and spatial structure for the first time in 2013 in the world (Nat. Commun. 4, 2527 (2013)), they recently made important progress in this direction: for the first time The photon orbital angular momentum is entangled between the two memory cells. The team used two magneto-optical traps to prepare two cold-atom clusters. One of the cold-atom clusters used a spontaneous Raman process to create entanglement between single-photon and atomic ensemble.
Then the Raman storage protocol is used to store the photon in another cold atomic mass as a storage medium, so that orbital angular momentum entanglement is stored between two atomic ensembles. In order to test the entanglement properties, they transfer the entanglement between the atomic ensembles to the photons. Quantum tomography technique was used to reconstruct the density matrix of the entangled state. The degree of entanglement was characterized by calculating the storage fidelity, verifying the two-photon CHSH inequality and examining the two-photon interference visibility. The experimental results clearly show that the orbital angular momentum entanglement can be stored with high fidelity. This work is of great significance for realizing high-dimensional quantum relays and long-distance large information quantum information transmission.
This work was funded by the State Fund Committee, the Chinese Academy of Sciences, the Ministry of Science and Technology, and the Center for Quantum Information and Quantum Technology Collaborative Innovation.
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