While the excitement in the area of quantum computing is fully justified by the new theoretical developments, year by year scientists have discovered new limitations of quantum computing devices. In particular, unitary operation decomposition provides a number of problems including the applications to hardware with fixed topology. Moreover, quantum algorithms have been proved to be sensitive to noise, which may impact the results of the computation. This resulted in the development of a new branch of quantum computing, namely the theory of quantum error-correcting codes. This aspect became even more critical when first commercial quantum computing systems became available. Furthermore, for quantum cryptographic protocols, hardware attacks, based on the security holes of conventional electronics, have been discovered. This demonstrated that the theoretical security confirmed by the laws of physics in the ideal environment could lead to the creation of insecure protocols the real-world applications.

The goal of this project is to develop theoretical methods suitable for analysing the impact of quantum program alternation -- input data modification or imprecise implementation of the algorithm -- on the efficiency of quantum algorithms. Here quantum program is the sequence of quantum operations and the quantum representation of input data which are sent to the quantum processor. In some ceases we can consider quantum program alternation as a action of a malicious party and in this scenario we can understand it as an attack on quantum processor or quantum program.