Do you use online banking? Buy things on Amazon? Or post stories on Facebook? If so, then Quantum Computing can have a major impact on how you do things on the internet. To explain how, we must start with understanding internet security.
Have you ever noticed that some websites, like your banking site for example, start with https and show a little lock next to the address bar, while others start with http and do not have the lock? The https and the lock mean that it is a secure site and any information you enter on a form is guaranteed to only be readable by the official owners of the site. This works through a process of encryption using the secure sockets layer (ssl).
Current encryption techniques work off of a precept that factoring numbers, especially extremely large prime numbers that have been multiplied together, is an extremely hard problem for a computer to solve. Modern encryption techniques multiply two 2048-bit prime numbers together to establish an encryption scheme. The two prime numbers represent the client and server and each one knows the other prime, but no one else listening on the line knows either prime.
To factor such a large prime number will take a nearly infinite time with current computer technology. Every digit must be sampled independently, each taking two steps, and even with the most powerful computers it would take more than the current age of the universe to factor the primes. A good mathematician can factor them by hand in about a decade, by which time your bank transaction information is useless.
This is where quantum computers come into play. A quantum computer works off the concept of a qubit. A qubit can be thought of as a coin flipping in the area, we do not know whether it is heads or tails until we catch it and look. It has equal probability of being either one before it lands. This state is known in the quantum computing world as superposition. Another power of a qubit is called entanglement. Entanglement is where two qubits exactly mirror each other; regardless of what happens, they are always in either equal and opposite states or exactly the same state, depending on how they became entangled.
These two properties of qubits allow a quantum computer to know all the possible outcomes for any possible input instantaneously. As a result, they can factor very large prime numbers very quickly, in effect, breaking modern cryptography. This is bad news for your bank account, but the good news is that this requires a large, fault-tolerant quantum computer.
Today we have small, noisy, intermediate-scale quantum (NISQ) computers. NISQ systems have relatively small qubit counts of less than 50 qubits. The qubits in these systems are noisy and error prone, creating problems with successful results in things like breaking encryption, and they are too small. They can only factor up to 50-bit numbers.
Current predictions are that we are between 10-20 years away from having a fault-tolerant quantum computer, with 2048 qubits capable of breaking modern encryption, and the banking industry is already working on quantum encryption techniques in preparation for the future. So there is no real need to worry for at least a decade.