Scientists have successfully prepared scalable polyatomic entangled states

Academician Pan Jianwei and Professor Yuan Zhensheng of University of Science and Technology of China, together with Associate Professor Ma Xiongfeng of Tsinghua University and Associate Researcher Zhou You of Fudan University, prepared polyatomic entanglement states by preparing two-dimensional atomic arrays, generating atomic bit entangled pairs, and connecting entangled pairs step-by-step expansion using ultracold atoms bound in the optical lattice, and regulated and observed their entanglement properties by microscopy, taking an important step towards the preparation and measurement of large-scale neutral atomic entanglement states. The results of this research were recently published in Physical Review Letters.

Schematic diagram of multibody entangled states in quantum gas microscope and crystal lattice Courtesy of China University of Science and Technology

Quantum entanglement is the core resource of quantum computing, and the power of quantum computing will increase exponentially with the increase in the number of entangled bits. Therefore, the preparation, measurement and coherent manipulation of large-scale entangled states are the core problems in this research field. Among the many physical systems that realize qubits, the ultracold atomic bits in the optical lattice have good coherence, scalability and high-precision quantum manipulation, making them one of the ideal physical systems for quantum information processing.

Since 2010, the research team of the University of Science and Technology of China has systematically studied the many-body phase transition, atomic interaction, entropy distribution dynamics, etc. of atoms in the optical lattice, and achieved more than 1,000 pairs of atomic entanglement states with entanglement fidelity of 99.3% in 2020. This series of research work has promoted the improvement of the fidelity of atomic entanglement and the enhancement of the ability of atomic parallel manipulation, laying the foundation for the expansion of the connection into a larger multi-atomic entanglement state, and then the research of quantum computing.

However, in the previous work, due to the insufficient technical ability to manipulate single-atom bits, the large phase drift of the optical lattice, and the lack of effective methods for determining polyatomic entanglement, further connection entanglement pairs and measurement and control of polyatomic entanglement states encountered bottlenecks.

Schematic diagram of the experimental preparation process of one-dimensional and two-dimensional entangled states Courtesy of China University of Science and Technology

In order to solve the above problems, the team of Pan Jianwei and Yuan Zhensheng developed a new isoarm cross-beam interference and spin-dependent superlattice system, and integrated the self-developed single-lattice point resolution, wide-band achromatic quantum gas microscope and multiple sets of digital micromirrors for spot shape editing, which have the ability of multi-atom global parallel and local single-grid point measurement and control, and achieve long-term stability of lattice phase.

On this basis, the team obtained the preparation and in situ observation of the two-dimensional array of atoms with a filling rate of 99.2%, and selected 49 pairs of atoms to prepare entangled Bell states, with an average fidelity of 95.6% and a lifetime of 2.2 seconds.

Further, they used entanglement gates to connect adjacent entangled pairs, and prepared 10-atom one-dimensional entangled chains and 8-atom two-dimensional entangled blocks, which broke through the bottleneck of atom entanglement pair connections and multi-atomic entanglement determination in optical lattices for the first time, and laid a foundation for large-scale optical lattice quantum computing and simulation.

According to the reviewers, “This work is an important step towards measurement-based quantum computing using optical lattice systems. (Source: Wang Min, China Science News)

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