Preparation of Large-scale High-fidelity Quantum Entanglement Pairs in Supercooled Atomic Optical Lattice

[ Instrument R&D of Instrumentation Network ] Recently, professors Jianwei Pan and Yuan Zhensheng from the University of Science and Technology of China have made progress in the quantum computing and simulation research of supercooled atoms. They have theoretically proposed and experimentally implemented a new mechanism for deep cooling of atoms. The synchronous preparation of 1250 pairs of high-fidelity entangled states of atoms in the crystal lattice lays the foundation for large-scale quantum calculation and simulation based on the ultracold atomic optical lattice.

Based on the basic principles of quantum mechanics, quantum computing and simulation are considered as subversive technologies that promote high-speed information processing in the post-Moore era, and are expected to solve major scientific and technical problems such as high-temperature superconducting mechanism simulation and password cracking. Quantum entanglement is the core resource of quantum computing. The capacity of quantum computing will increase exponentially with the increase of the number of entangled bits. Therefore, the preparation, measurement and coherent manipulation of large-scale entangled states are the core issues in this research field. The usual way to achieve large-scale entangled states is to first prepare a large number of entangled particle pairs, and then connect them through quantum logic gate operations to form multi-particle entanglement. Therefore, the simultaneous preparation of high-quality entangled particle pairs is the primary condition for achieving large-scale entangled states. Over the past decade, there have been many experiments demonstrating the feasibility of manipulating multiple qubits for information processing in systems such as photons and neutral atoms. However, in previous work, due to the quality of the entangled pair and the manipulation accuracy of the quantum logic gate, the maximum entangled state distance that can be prepared at present is still very entangled in the number of entangled bits and fidelity required for practical quantum computing and simulation. Big gap.

Among the many physical systems that realize qubits, optical lattice supercold atomic bits and superconducting bits have good scalability and high-precision quantum maneuverability, which is the first system that can achieve large-scale quantum entanglement. Since 2010, the research team of the Chinese University of Science and Technology has cooperated with the University of Heidelberg in Germany to carry out joint research on scalable quantum information processing based on the ultracold atomic optical lattice. In the previous study, the team used Rb-87 supercold atoms to prepare more than 600 pairs of supercold atom entangled states with a fidelity of 79% [Nature Physics 12, 783 (2016)], and used the system to control special rings The exchange interaction produces a four-body entangled state, simulating the arbitrary sub-excitation model in topological quantum computing [Nature Physics 13, 1195 (2017)]. In the above experiment, the temperature of the atoms in the lattice is too high (about 10 nK), which makes the filling defects of the atoms in the lattice greater than 10%, which forms a larger polyatomic entangled state and improves the entanglement fidelity for the entangled atom pairs. Have a great impact.

This recent study for the first time proposed a new refrigeration mechanism that uses a staggered lattice structure to soak cold atoms in an insulated state into a superfluid state, through efficient exchange of atoms and entropy between the insulated and superfluid states, The heat in the system is mainly stored in the form of super-fluid low-energy excitation, and then the super-fluid state is removed by precise control means, thereby obtaining a perfectly filled lattice with low entropy. This experiment realized this cooling process, which reduced the entropy of the system by 65 times after cooling, reached a record low entropy, and greatly increased the atomic filling rate in the lattice to more than 99.9%. On this basis, the research developed a two-atom-bit high-speed entanglement gate to obtain 1250 pairs of entangled atoms with an entanglement fidelity of 99.3%.

The new refrigeration technology in this study helps to deep-cool the super-cooled Fermi subsystem, enabling the system to reach the harsh temperature zone that simulates the physical mechanism of high-temperature superconductivity. The research team will also prepare entangled states of tens to hundreds of atomic bits by connecting multiple pairs of entangled atoms for single vector calculation and quantum simulation research of complex strong correlation multi-body systems.

Related achievements were published in "Science" in the form of "First Release". Reviewers believe that this achieves the lowest entropy it knows in atomic bits, and that it is in such a large (10,000 atoms) system; it reports high fidelity in neutral atoms it knows. Bit quantum gate; the development of new lattice quantum gas refrigeration technology is an important goal of studying new physical states and meeting the needs of quantum information processing. This research is a breakthrough to achieve such a large entropy reduction. The research work was supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences, the Ministry of Education, and Anhui Province.