From the MIT Technology Review:
Back in 1996, a quantum physicist at Bell Labs in New Jersey published a new recipe for searching through a database of N entries. Computer scientists have long known that this process takes around N steps because in the worst case, the last item on the list could be the one of interest.
However, this physicist, Lov Grover, showed how the strange rules of quantum mechanics allowed the search to be done in a number of steps equal to the square root of N.
That was a big deal. Searching databases is a foundational task in computer science, used for everything from finding telephone numbers to breaking cryptographic codes. So any speed-up is a significant advance.
Quantum mechanics provided an additional twist.