The reason a quantum computer can achieve performance orders of magnitude faster than a classical computer is because it can exploit the quantum mechanical principles of superposition and entanglement and achieve unprecedented amounts of parallelism without requiring the multiple replication of hardware that would be required in a classical computer.
Superposition can occur when the basic data element in a quantum computer, called a qubit, is in both the 0 and the 1 state simultaneously. Some theorists have proposed this the different states exist in a separate parallel reality or multiverse. Unlike a classical bit which is in either the 0 or the 1 state, but not both, a logical operation performed on a qubit can provide results for both an input of 0 and an input of 1 at the same time with the same piece of hardware. When multiple qubits are arranged in a register the available parallelism can be huge since each additional qubit increase the parallelism by a factor of 2.
Have you ever heard the story of identical twins who are so close that when something happens to one, the other will feel it even if they are thousands of miles apart? The other key phenomena, called entanglement, is like that on a particle basis. If you perform an operation on one element of the entangled pair, it will automatically impact the other one. Leveraging entanglement can provide some very interesting applications, such as hack-proof, interception-proof distribution of quantum keys for the ultimate in data security.