Quantum entanglement is a phenomenon in quantum mechanics where two or more particles become correlated in such a way that the state of one particle cannot be described independently of the state of the other particles. This correlation remains even when the particles are physically separated by large distances.
The concept of entanglement does not depend on the size or nature of the particles involved. It can occur between individual elementary particles such as electrons or photons, as well as larger systems such as atoms, ions, or molecules. In principle, any two or more quantum systems can become entangled if they interact in a way that entangles their states.
However, it is important to note that the size of a system does not necessarily determine the significance or impact of its entanglement. The significance of quantum entanglement lies in its potential applications for quantum information processing, quantum communication, and fundamental tests of quantum mechanics. While there have been notable experiments entangling larger and more complex systems, such as ions or superconducting circuits, there isn't a concept of a "biggest" thing that has been quantum entangled.
In summary, quantum entanglement can occur between particles or systems of any size, and the significance lies in its applications rather than the size of the entangled objects.