Impacts of quantum computing on Theoretical Computer Science
One major impact is that quantum computing gave us a polynomial time algorithm to solve the integer factoring problem which is not known to be efficiently solvable on classic computers. This partially motivated the development of public key cryptography that does not depend on the hardness of factoring problem.

Efficient quantum algorithm for an NP-complete problem would have the greatest impact on TCS since it would give us insights into the fundamental differences between the computational power of classical and quantum algorithms (assuming classic deterministic algorithms can not solve NP-complete problems in polynomial time) .