Quantum cryptography is marches towards secure communication by using quantum protocols. Number of quantum protocols has been evolved based on an entanglement in three decades; similarly during this meanwhile non-entanglement based protocols have been evolved within the same period also. Among number of different protocols a torch bearer was BB84 protocol. Even though different quantum communication protocols exist, the BB84 protocol proved its application by initial experiments whereas most of the other protocols are theoretical which marches towards the practical application yet. But in quantum mechanics principle, cryptography based on an entanglement and superposition of entangled particle. Furthermore, challenges ahead are development and design high sensitive equipments for measurement of an entangled particle position at output end. Particle entanglements open a new door for computation worlds such as speedup, security. In this article, we discuss quantum protocols, their challenges, and applications based on above discussion.

In this note, we look into two quantum algorithms, Deutsch-Josza’s and Shor’s algorithms. An attempt made to analyze classical as well as quantum parts computation. With that, analyze classical as well quantum parts complexities.