A Qubit error rate of QKD BB84 protocol

[Pattarasak]

Hello everyone, I don't know how to measure the QBER of BB84 protocol in a realistic experiment.In the most paper show the data which is only the number but do not show the unit of data, what is the unit of these data?

 

[Cael]

The Quantum Bit Error Rate (QBER) is the measurement of the percentage or probability of bit error across the quantum channel during key distribution. After obtaining the raw key, QBER can be calculated by taking the length of erroneous bits divided by length of raw key. In BB84 protocol, if an Eve intercept every qubits, QBER is 25%. How to calculate: ½(0) + ½(½) = ¼. (simply means half of the time, Eve would have use the correct basis, other half, she would use wrongly and half of that time where she used it wrongly, Eve would be discovered and that is reflected in QBER.