Optical Cavity Enhancement Experiment Of DLCZ Writing Excitation Process In Atomic Ensemble

In the 1980 s,with the continuous improvement of quantum theory and scheme,quantum information,as a new research field,has attracted people’s attention.As the most important and core part of quantum information,the most attractive characteristic of quantum communication is that it can realize the secure transmission of information on the physical level,and this security is based on a strange quantum state-photon entangled state.Quantum storage is the key technology to realize long-distance quantum communication and construct optical quantum network.It requires long-time storage and efficient coherent readout of optical quantum states.At present,many physical processes have been used to realize quantum storage,such as electromagnetically induced transparency(EIT),spontaneous Roman scattering(SRS),gradient echo technology,atomic frequency comb(AFC)and far detuning Roman interaction,etc.SRS is an effective method to realize quantum storage technology.Cold atom ensemble has rapidly become the core carrier of quantum storage and quantum communication due to the collective enhancement effect and the longer coherence time compared with hot atom.Since Duan luming and others proposed the Duan-Lukincirac-zoller(DLCZ)scheme to construct the entangled interface between photon and atom by using the spontaneous Raman scattering process in atomic ensemble in 2001,various schemes of quantum repeaters based on DLCZ quantum memory have been proposed one after another,and some of them have been demonstrated in experiments.The field of quantum information based on atoms has made great progress.It is difficult to meet the practical use of quantum repeater due to the low success rate of Raman process in recent years.People began to explore how to improve the generation rate of entangled photons,such as temporal multimode memories,spatial multimode memories and so on.These schemes have successfully doubled the generation rate of entanglement between photons and atom.In 2010,C.Simon and others proposed that the probability of entangled photon pairs can be improved by using the resonance of Stokes photon and optical cavity.In 2020,Lukas Heller et al,realized this scheme for the first time by placing atoms in an optical cavity,and realized the increase of the generation probability of entangled photon pairs.Since then,the scheme of combining DLCZ with cavity has been widely concerned.In this paper,the entanglement of photon and atom is produced by spontaneous Raman scattering in cold atom ensemble.By using the optical cavity to enhance the interaction between photons and atoms,the probability of Stokes photons generation in DLCZ writing process is increased by 8.7 times.Generation of spin-wave-photo entanglement based on spatial multimode memories is fabricated,and the feedback control system of field programmable gate array(FPGA)is used to realize 18 times temporal multimode memories.The main work includes the following parts.(1)Optical cavity enhancement experiment of DLCZ writing excitation process in atomic ensemble.Based on the single-mode DLCZ experiment,the atomic ensemble is placed in a standing wave cavity which resonates with Stokes photons to enhance the coupling strength between Stokes photons and atoms.The experimental results show that the probability of Stokes photons is 8.7 times higher than that without cavity,which is in good agreement with the theory.This work provides an experimental basis for improving the generation of photon atom entanglement.(2)The generation of atom-photon entanglement source based on temporally multimode storage.A series of write pulses applied to the atomic ensemble at different times and space angles.We have obtained 19 photon spin wave mode pairs.Combined with the feedback control system of FPGA,the spin wave modes associated with Stokes photons are read out.Through this scheme,we have obtained a temporally multimode entangled interface between light and atom.The generation probability of entangled photon pair is18.8 times that of single-mode experiment.The lifetime of entangled source is 30 μs,the bell parameter is 2.30 ± 0.02,and the fidelity is 85.9%.This work provides a feasible way to improve the rate of entanglement distribution in quantum repeater.