Eavesdropping on a Quantum Channel with a Unitarily Interacting Probe

Eavesdropper tapping communication links is a common problem encountered in communication systems. The famous no cloning theorem and the uncertainity principle are instrumental in ensuring secrecy of classical information when transmitted using quantum states. With Wyner's wiretap channel as motivation, we study the effect of a unitarily interacting probe on the extraction of information by an eavesdropper. We motivate the theoretical results by considering a practical example of a unitary interaction between the transmitted qubit and the probe used by an eavesdropper. The role played by entanglement is also studied in the setting of single shot communication between sender and receiver nodes.