  The quantum internet is envisioned as the ultimate stage of the quantum
revolution, which surpasses its classical counterpart in various aspects, such
as the efficiency of data transmission, the security of network services, and
the capability of information processing. Given its disruptive impact on the
national security and the digital economy, a global race to build scalable
quantum networks has already begun. With the joint effort of national
governments, industrial participants and research institutes, the development
of quantum networks has advanced rapidly in recent years, bringing the first
primitive quantum networks within reach. In this work, we aim to provide an
up-to-date review of the field of quantum networks from both theoretical and
experimental perspectives, contributing to a better understanding of the
building blocks required for the establishment of a global quantum internet. We
also introduce a newly developed quantum network toolkit to facilitate the
exploration and evaluation of innovative ideas. Particularly, it provides dual
quantum computing engines, supporting simulations in both the quantum circuit
and measurement-based models. It also includes a compilation scheme for mapping
quantum network protocols onto quantum circuits, enabling their emulations on
real-world quantum hardware devices. We showcase the power of this toolkit with
several featured demonstrations, including a simulation of the Micius quantum
satellite experiment, a testing of a four-layer quantum network architecture
with resource management, and a quantum emulation of the CHSH game. We hope
this work can give a better understanding of the state-of-the-art development
of quantum networks and provide the necessary tools to make further
contributions along the way.
