Attaining Scalable Multipartite Entanglement Using Ultracold Atoms Trapped in an Optical Lattice

A team of researchers, including scientists from the University of Science and Technology of China (USTC) at the Chinese Academy of Sciences (CAS), Tsinghua University led by Ma Xiongfeng, and Fudan University led by Zhou You, have made significant progress in creating and measuring scalable multipartite entangled states.

Through the utilization of ultra-cold atoms confined in optical lattices, the research group achieved the preparation of multi-atom entangled states. This was accomplished by forming a two-dimensional atomic array, generating pairs of entangled atom qubits, and subsequently linking these pairs in a sequential manner. The findings of this study have been published in Physical Review Letters, and the American Physical Society recognized this achievement with a feature in Physics Magazine titled “Milestone for Optical-Lattice Quantum Computer.”

Quantum entanglement, a fundamental phenomenon in quantum computing, leads to exponential growth in capabilities as the number of entangled qubits increases. Consequently, the preparation, measurement, and coherent manipulation of large-scale entangled states present significant challenges in the realm of quantum research.

Among the various physical systems utilized for implementing quantum bits (qubits), ultracold atomic qubits in optical lattices exhibit outstanding coherence, scalability, and high-precision quantum control. These characteristics position them as an ideal choice for executing quantum information processing.

Since 2010, the USTC research team has been systematically investigating multibody phase transitions, atomic interactions, and entropy distribution dynamics within optical lattices. By the year 2020, they achieved an entanglement fidelity of 99.3% with over 1,000 pairs of entangled atoms. These studies paved the way for improving the fidelity of atomic entanglement and enhancing the capability of parallel atomic control, providing a foundation for larger multi-atom entangled states and advancing quantum computing research. However, earlier efforts encountered challenges due to limited control over individual atomic qubits, notable phase shifts in optical lattices, and a lack of effective methods for detecting and controlling multi-atom entanglement states.

To overcome these technical hurdles, the team led by Pan Jianwei and Yuan Zhensheng developed an innovative equal-arm, cross-beam interference, and spin-dependent superlattice system. They integrated self-developed single-lattice resolution, wide-band achromatic quantum gas microscopy, and multiple sets of digital micromirrors for shaping spots. This setup enabled both global parallel measurement and control of multi-atom configurations, as well as local measurements at single grid points.

Through this innovative approach, they achieved a 99.2% filling rate of a two-dimensional atomic array and prepared entangled Bell states with an average fidelity of 95.6% and a lifespan of 2.2 seconds. Additionally, they interconnected adjacent entangled pairs to create a 10-atom one-dimensional entangled chain and an eight-atom two-dimensional entangled block.

This groundbreaking work represents a significant stride toward the realization of large-scale quantum computation and simulation utilizing optical lattices.

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