No, a single photon cannot be split into four entangled photons simultaneously. The process of splitting a photon typically involves interactions with certain materials or physical systems, such as crystals or nonlinear optical processes. These processes can generate multiple photons from an initial photon, but they do not generate entangled photons by default.
Entangled photon pairs are commonly generated through a process called parametric down-conversion, which involves a nonlinear crystal. In this process, a high-energy photon interacts with the crystal, resulting in the creation of two lower-energy photons known as signal and idler photons. These two photons are typically entangled, with their properties becoming correlated.
While it is possible to generate entangled photon pairs using specific experimental setups, extending this to four entangled photons simultaneously is more complex. It requires additional processes and careful experimental design. Generating entangled states with more than two photons becomes increasingly challenging due to technical limitations and the complexity of maintaining entanglement between multiple particles.
In summary, while it is possible to generate entangled photons, splitting a single photon into four entangled photons simultaneously is not a straightforward process and typically requires more advanced experimental techniques.