Recently, Li Chuanfeng and Zhou Zongquan's research group, led by academician Guo Guangcan of the University of Science and Technology of China, realized on-demand quantum storage of photons in the communication band based on erbium-doped waveguides, which is an important step towards the construction of large-scale optical fiber quantum networks. The results were recently published in the international academic journal Physical Review Letters.
Quantum memory is the core device of quantum network. By reading entangled photons on demand, the exponential loss in long-distance optical fiber transmission can be reduced to polynomial loss. In order to use the existing optical fiber network to build a quantum network, the quantum memory should work in the communication band. The rare earth erbium ion has a unique optical transition in the communication band, and is an important candidate material for realizing quantum memory in the communication band. However, the readout time of the existing quantum memory in the communication band is preset before the photon is written, and it is impossible to realize on-demand readout.
The research group of Li Chuanfeng and Zhou Zongquan independently processed the optical waveguide on the erbium-doped yttrium silicate crystal using laser direct writing technology, and directly pasted and integrated ordinary single-mode optical fibers at both ends of the waveguide. In order to achieve on-demand reading, the research team further used electron evaporation technology to process on-chip electrodes on both sides of the waveguide, so as to use the electric field-induced Stark effect to control the coherent evolution of erbium ions in the waveguide in real time. By polarizing the electron spins of erbium ions and initializing their nuclear spin states, the photon storage efficiency is increased to 10.9%, which is a 5-fold improvement compared to previously reported quantum storage for integrated communication bands. The fidelity of the on-demand quantum storage regulated by the electric field reaches 98.3%, far exceeding the classical limit considering the storage efficiency and photon statistics.
This achievement realizes on-demand quantum storage in the communication band based on erbium ions, and this optical fiber integrated device can be directly connected to the existing optical fiber network. In the field of classical communication, the invention of erbium-doped fiber amplifiers has made long-distance optical fiber communication a reality. Similarly, quantum storage based on erbium ions can also be used to overcome the exponential loss in long-distance quantum communication, making it possible for erbium ions to be used again in quantum networks. important role in construction.
This achievement was highly praised by the reviewers: "Compared with previous work, this work has made important progress, especially the direct bonding of the optical fiber to the optical waveguide, which supports stable operation in a low temperature environment."
