UWSP achieves milestone in optical quantum computing entanglement gate fidelity exceeds 99- for the first time
This work is the first time to improve the purity and full homogeneity of the Rydberg single-photon source to more than 99.9%, and to realize the highest fidelity optical quantum logic gate based on this single-photon source in the world. The research results are expected to open up new prospects for important quantum applications such as optical quantum information processing and distributed optical quantum systems.
Conceptual diagram of an optical quantum logic gate
Single-photon sources are one of the core quantum resources required for quantum information and precision measurement research. Many important quantum optical applications have extremely high requirements on the quality of single photons, for example, to satisfy applications such as all-optical quantum repeaters and cluster state optical quantum computing, the purity of single photons must be more than 99.9% and the full homogeneity must be greater than 99%. In the past decades, different physical systems have been developed to generate single photons, and although the quality of single photons has improved dramatically, achieving a single photon source that satisfies both high purity and high all-identity remains a major challenge.
In recent years, quantum physics research based on Riedberg atoms has achieved rapid development, and the extremely strong and controllable interactions between Riedberg atoms provide new possibilities for efficient quantum manipulation at the single-photon level. Prof. Lin Li's group at Huazhong University of Science and Technology (HUST) has been devoted to the development of quantum information processing and precision measurement technology based on Riedelberg atoms for a long time. In this study, the group has achieved high precision excitation and manipulation of super-atomic quantum states by using the interaction between Riedberg atoms, and prepared a high quality single photon source with 99.95% purity and 99.94% full homogeneity based on this.
Schematic diagram of single photon source preparation and quantum logic gate experiments
The group has also conducted important research on the application of single-photon sources: optical quantum logic gates. Quantum logic gate is the core unit of quantum computing and other important applications, and its fidelity directly affects the scalability of quantum systems. Among the existing quantum bits, photons are the best carriers for long-distance transmission of quantum information, so achieving high-fidelity optical quantum information processing is crucial for building large-scale quantum networks for distributed quantum computing. knill, Laflamme and Milburn proposed in 2001 that photon-photon quantum logic gates can be realized using quantum interferometry and projection measurements (KLM scheme ), but the fidelity of the optical quantum logic gate in this scheme is limited by the quality of the single photon source. To achieve a quantum logic gate with >99% fidelity based on this scheme, the purity of the single photon must be >99.3% and the full homogeneity must be >99%. These stringent specifications have made it impossible to achieve optical quantum logic gates with greater than 99% fidelity.
In this study, Prof. Lin Li's group demonstrated near-perfect two-photon quantum interference using a high-quality Riedberg single-photon source, applied it to an optical quantum logic gate experiment based on the KLM scheme, and successfully increased the truth table fidelity to 99.84%. Using this high-fidelity optical quantum logic gate, the group further demonstrated the establishment of quantum entanglement between two uncorrelated single photons and performed quantum entanglement measurements by quantum lamination and Bell's inequality, etc. The fidelity of the entanglement gate reached 99.69%. Compared with the previous results of similar experiments, this study reduces the error (distortion) of optical quantum logic gates by more than one order of magnitude.
Riedberg Quantum Optics Experimental Facility
The research will contribute to the development of all-optical quantum information processing, in which high-quality single-photon sources and high-fidelity quantum logic gates can be used to prepare important multi-photon entangled states such as cluster states, and to build fault-tolerant optical quantum computing systems. To further increase the number of entangled photons, the group will also explore a new scheme of coupling Riedberg atoms with high-fidelity resonant cavities to enhance the efficiency of optical quantum state generation. In addition, Riedberg atoms are also an excellent platform for quantum computing. Using their excellent light-matter quantum interaction capability, the high quality optical quantum states realized in this study can connect multiple Riedberg quantum nodes, which is expected to build a quantum computing network with higher scalability. The group also developed a high-precision Rydberg atom tuning technique in this research, which lays the foundation for future quantum precision measurements based on Rydberg atoms.
Shuai Shi, a postdoctoral fellow at the School of Physics, and Biao Xu, Gensheng Ye and Associate Professor Kuan Zhang, PhD students at HUST, are the co-first authors of this work, and Professor Lin Li and Associate Professor Su Tochin are the co-corresponding authors. This work was supported by the National Key Research and Development Program of the Ministry of Science and Technology, the National Natural Science Foundation of China, and the National Major Science and Technology Infrastructure for Precision Gravimetry of Huazhong University of Science and Technology.
