  Securing information transmission is critical today. However, with rapidly
developing powerful quantum technologies, conventional cryptography techniques
are becoming more prone to attacks each day. New techniques in the realm of
quantum cryptography to preserve security against powerful attacks are slowly
emerging. What is important though now is the fidelity of the cryptography,
because security with massive processing power is not worth much if it is not
correct. Focusing on this issue, we propose a method to enhance the fidelity of
quantum cryptography using maximally entangled qubit pairs. For doing so, we
created a graph state along a path consisting of all the qubits of ibmqx4 and
ibmq_16_melbourne respectively and we measure the strength of the entanglement
using negativity measurement of the qubit pairs. Then, using the qubits with
maximal entanglement, we send the modified encryption key to the receiver. The
key is modified by permutation and superdense coding before transmission. The
receiver reverts the process and gets the actual key. We carried out the
complete experiment in the IBM Quantum Experience project. Our result shows a
15% to 20% higher fidelity of encryption and decryption than a random selection
of qubits.
