Quantum Frequency Conversion Based on Resonant-Type Quantum Nonlinear Optics
演講者 : 鄭晉堯 博士候選人 (成大物理系)
演講地點 : 理學教學新大樓物理系3F 36369會議室
演講時間 : 2021 / 10 / 28 14:41
Due to the advantages of fast propagation and weak interaction with the environment, photons or flying qubits have become one of the excellent quantum carriers that scientists are committed to developing in quantum communication and quantum computing. However, in a quantum network connected by photons, the wavelengths of photons applied to various quantum nodes are quite different. To enable all nodes to work under optimal conditions, the realization of efficient quantum frequency conversion (QFC) becomes a key issue in the construction of optical quantum network. In this doctoral dissertation, we propose and demonstrate a high-efficiency QFC based on resonance-type quantum nonlinear optics. This resonant QFC uses a four-wave mixing (FWM) process based on the electromagnetically induced transparency (EIT) mechanism. Unlike far-resonant nonlinear systems, this resonant EIT-based FWM requires a relatively small pump light intensity and medium density. This feature makes the EIT-based QFC not cause additional nonlinear processes and accompanying noise photons, making it have an excellent performance in the fidelity of the quantum state of the converted photons. Furthermore, by leveraging the characteristics of EIT, the spontaneous emission loss, which is the shortage of the resonant system, can be considerably suppressed. Thus, the EIT-based FWM system allows us to take advantage of the strong interaction strength without paying for the spontaneous emission loss, and a high-fidelity low-loss QFC can be implemented. In the theoretical model, we use the general reservoir theory to study a double-Lambda QFC based on a resonant FWM. Due to the effect of EIT, this resonant QFC can considerably suppress vacuum field noise; consequently, the converted photon can inherit the quantum state of the input photon with high fidelity. Our research demonstrates that if the conversion efficiency (CE) of the EIT-based QFC is close to 100%, the wave function and quadrature variance of the converted photon are almost the same as the input probe photon. In addition, the fidelity in the multi-mode case is also studied in our quantum model. Based on our theoretical calculation, a Fock state single photon with a duration of 200 ns can achieve a CE of 92.4% with a fidelity of 0.9 under an optical depth (OD) of 300. In the experiment, we demonstrate the use of EIT-based double-$\Lambda$ FWM for efficient frequency conversion, and achieve a CE of 91.2% with an OD of 130 in cold 87Rb atoms. This doctoral dissertation has carried out a detailed research on the low-loss, high-fidelity QFC of resonant-type quantum nonlinear optics from both theoretical and experimental aspects. The current work provides another promising scheme for the future development of efficient QFC applications in quantum communication, network and computing.