## Quantum Layer

When characterizing a quantum key distribution system, the two main figures of merit that come into play are the *Quantum Bit Error Rate (QBER)* and the *Secret Key Rate*.

The **QBER** is the measurement of the error probability in the key distributed across the quantum channel. This value allows the users to estimate the maximum amount of information that an eavesdropper could have on the key. It serves as an input to the key distillation protocol that transforms raw keys into the secret key.

The **Secret Key Rate** is a value that corresponds to the number of secret bits produced by a quantum key distribution system after key distillation. These secrets bits are stored in a key buffer and then passed on to the Quantum key server.

The rate at which keys are exchanged over the three links connecting the CERN, UNIGE and HEPIA is collated from the logs and analysed with respect to parameters such as error probabilities in key distribution & secret key generation with respect to time.

Below is the graphical representation of the QBER and the Secret Key Rate.

### Quantum Bit Error Rate (QBER)

### Secret Key Rate

Please check the Problems. This page lists relevant problems occured on the SwissQuantum network.