Category:Prepare and Measure Network Stage

The second network stage offers end-to-end connection between nodes. Any node here is allowed to prepare one qubit state and transmit the resulting state to any other node, which then can receive and measure it. In this case, the other node can either measure the qubit or conclude that it is lost.

Transmissions and measurements can be post-selected, a signal that the qubit is lost may be generated instead. For instance, the receiving node is allowed to ignore non-detection events and conclude that such qubits are lost. If the sender can prepare an entangled state of two qubits then this stage also includes the case in which the sender can prepare an entangled state and send the two entangled qubits to two different nodes in the network. This entanglement distribution is also post-selected. However this post selected prepare and measure functionality is not equivalent to transmitting arbitrary qubits over the network.

Applications

This stage allows tasks like QKD. Another class of protocols in this stage is in the domain of two-party cryptography. Here, there is no eavesdropper, but rather Alice and Bob themselves do not trust each other.

Relevant Parameters

• Distances ${\displaystyle \epsilon _{T}}$ and ${\displaystyle \epsilon _{M}}$ from the ideal transmission and measurement operations. These distances are diamond norm distance between the states obtained from ideal quantum channels, measurement and real (noisy) quantum channels and measurement.
• Probability ${\displaystyle p}$ that the state is not lost.