Quantum entanglement, a crucial resource in quantum information science, describes a unique type of quantum correlation system. When two or more subsystems are entangled, their states are inseparable. The measurement results of this entangled system exhibit correlations that are fundamentally different from classical statistics, reflecting the non-local nature of quantum entanglement.

In recent years, the rapid advancement of quantum information science has deepened our understanding of the interplay between quantum systems and information science. The concept of a quantum network has emerged in academic circles. A quantum network typically consists of multiple interconnected qubits. Nodes within the quantum network are responsible for generating, processing, and storing quantum information. These nodes are connected through quantum correlation or entanglement channels, enabling high-fidelity quantum state transmission and distributing entanglement across the network.

Quantum entanglement is a key resource for constructing quantum networks and realizing quantum communication, quantum computing, and quantum precision measurement. To meet the demands of complex quantum information processing and quantum network construction, generating and regulating large-scale quantum entangled states across multimode of light, i.e., multimode quantum entanglement, has become a significant research challenge in quantum information science.

This review will focus on theoretical and experimental research regarding the preparation of quantum entangled networks, with a particular emphasis on continuous variable quantum optical systems. We provide an overview of three primary technical pathways for preparing the squeezed states in continuous variable quantum optics including optical parametric oscillator, parametric four-wave mixing, and related integrated quantum optical platforms.

One of the most used approaches for preparing multimode entangled states involves using the optical beam splitter network to couple multiple squeezed sources. However, this technical pathway imposes high requirements for loss and coupling control among the multiple quantum sources and linear optical networks, making it challenging to prepare large-scale entangled states. As a result, researchers have shifted their focus to other multimode methods to prepare large-scale entangled states. The main preparation schemes are based on spatial, temporal, and frequency degree of freedom of light.

Among the schemes based on various spatial modes, typical approaches include combinations of the spatial pixels, orbital angular momentum multiplexing, and cascading non-linear processes, with their quantum correlation characteristics primarily manifested in the spatial dimension. As to temporal modes, the time-domain multiplexing scheme is predominantly used to generate large scale entanglement with the correlation of time series. For frequency modes, optical frequency comb technology is primarily utilized to prepare multimode entanglement associated with the frequency domain.

With the significant development of the field of quantum information and the ongoing progress in experimental technology, the quantum network composed of multimode entangled states has emerged as a crucial quantum resource in the fields of quantum precision measurement and quantum information processing. Such entanglement-based quantum network has demonstrated quantum superiority in numerous experiments and applications, underscoring its growing significance. Therefore, it is imperative to further advance the construction and application of versatile quantum networks.