Junaid ur Rehman

Security of a control key in quantum key distribution

Quantum key distribution (QKD) schemes rely on the randomness to exchange secret keys between two parties. A control key to generate the same (pseudo)-randomness for the key exchanging parties incr...

Quantum channel discrimination without entanglement

We address the problem of unambiguous discrimination of quantum channels (UDQC) without entanglement. As our main result, we show that even in the absence of entanglement, partial UDQC (PUDQC) can still be performed—depending on the unknown given channel. We provide a necessary and sufficient condition for PUDQC and put forth a method to perform the PUDQC once the said condition is met. We propose the performance metrics that capture the expected performance of the PUDQC independent of the specific channels to be distinguished. Finally, we perform PUDQC on several qubit channel pairs as concrete examples and derive the proposed performance metrics for these channel pairs.

Quantum key distribution with a control key

Quantum key distribution (QKD) relies on randomness to exchange secret keys among the communicating parties. While ensuring the secrecy of the keys being distributed, independent randomness also causes to reduce the number of key bits that can be shared per quantum signal exchanged. Recently it was shown that it is possible to use pseudo-randomness in place of true randomness in the QKD without compromising the integrity of a QKD scheme. By the virtue of a short secret key — called a control key — shared among the key sharing parties, same pseudo-randomness can be generated at the transmitter and the receiver end that allow to obtain a higher key exchange rate. However, there are certain modifications which are necessary before pseudo-randomness can be safely employed in a QKD procedure. In this paper, we provide a modification of QKD schemes for a secure use with the control key. We modify the prepare-and-measure (BB84) type, and measurement-device independent protocols. We then verify the advantages of use of control key in terms of key rates for the modification of two QKD schemes.