New Method for Generating Quantum Entanglement Using Single-Qubit Rotations

Recent research has introduced a novel protocol for generating symmetric entangled states through single-qubit rotations in a unique quantum system. The study, titled "Entanglement generation via single-qubit rotations in a torn Hilbert space," was conducted by Tao Zhang, Zhihao Chi, and Jiazhong Hu, and is available on arXiv (arXiv:2312.04507).

The authors propose a method that utilizes spin-1/2 qubits placed in a resonator, which can be realized with atoms in optical cavities or superconducting qubits. By directing light or microwaves into the resonator, the system induces AC Stark shifts on specific angular-momentum eigenstates known as Dicke states. This process creates barriers that prevent transitions between adjacent Dicke states, effectively fragmenting the original Hilbert space. As a result, what appears to be a simple global single-qubit rotation becomes a complex operation that generates entanglement across the many-body system.

The researchers demonstrate that by optimally controlling energy shifts on the Dicke states, they can produce arbitrary symmetric entangled states with high fidelity. They also highlight the capability to create various useful states, such as W states, spin-squeezed states, and Greenberger-Horne-Zeilinger (GHZ) states, often in just one or a few steps. Notably, the spin-squeezed states can be generated in a single step, approaching the Heisenberg limit for precision.

This work establishes a pathway for universal entanglement generation using only single-qubit operations, which simplifies the control mechanisms typically required in quantum systems. The findings have direct implications for the development of variational quantum optimizers, which are compatible with existing technology. The full paper can be accessed at arXiv:2312.04507.