Researchers tested the limits of the quantum teleportation.

 Researchers tested the limits of the quantum teleportation. 

The researchers from the University of Stuttgart measured all four Bell states. The Bell states are full correlations between qubits that can be in states 0 or 1 or in superpositions. The reason why Bell states are interesting is that the quantum system requires two-qubit lines and all four states to back and forth communication. The problem with Bell state collapse is that the qubits that transmit information from point A to point B are opposite or mirror position to the qubit that transports information from point B to point A. 

The reason for that mirror symmetry is that the transmitting side of the qubit must be at a higher energy level than the receiving qubit. Only identical qubits can transport information without damaging the informational structure. When two identical qubits are side by side energy travels from the higher energy qubits to lower energy qubits.

"In the Barz group’s experiment with a two-stage interferometer auxiliary photons are used to generate distinct measurement patterns for all four Bell states, increasing the efficiency beyond the traditional limit of 50%. Credit: Jon Heras, Cambridge Illustrators." (ScitechDaily.com/Breaking the Quantum Limit: From Einstein-Bohr Debates to Achieving “Unattainable” Efficiency)

 When a qubit sends energy to another qubit the difference between energy levels decreases and information starts to run slower. Energy runs in a quantum system until both sides are at the same level. And that forms a standing wave between those sides which destroys the qubit. 

We can use the seesaw as the model of Bell states. Each end of those seesaws is one of the Bell states. If we consider that quantum entanglement is like a seesaw where information flows from a higher energy level to a lower one, then a two-way quantum network needs two seesaws that cross together. 

The thing is that information and energy always travel from higher energy levels to lower. When energy levels in the ends of the systems reach the same level it destroys the entire system. And then that thing destroys the quantum entanglement. 

But the thing that causes collapse in Bell states is this. When energy travels out from the higher energy level qubit its energy level decreases. Because there are four states in the qubit pair. That thing causes entropy in energy levels to rise. The reason for that is that there are forming whirls and waves to the qubit. 

Those things destroy the entire qubit and cause the destruction of the Bell states. In tests, the researchers tested the Bell states stability and ability to send information back and forth by using the Bell states. The thing is that the Bell states are a requirement for two-direction communication over the quantum network. 

https://en.wikipedia.org/wiki/Bell_state