What is quantum interference?
Amplitudes adding up or cancelling when they combine. Quantum algorithms use it to make wrong answers unlikely.
If two paths lead to the same result and their amplitudes have the same sign, the result becomes more likely. If the signs are opposite, they cancel and the result can become impossible.
A useful quantum algorithm is a sequence of gates arranged so that by the end, the amplitudes of wrong answers cancel and the right answer’s amplitude grows. For most problems nobody has found such a sequence, which is why quantum computers are expected to help with only some kinds of problems.
In the lessonsSee it in a simulation
Related
- AmplitudeThe number a qubit holds for each possible result. Squaring it gives the chance of that result.
- Quantum gateAn operation that changes the amplitudes of one or more qubits, the quantum version of a logic gate.
- Grover's algorithmA quantum algorithm, published by Lov Grover in 1996, that searches unsorted possibilities in about the square root of the usual number of tries.
- Shor's algorithmA quantum algorithm, published by Peter Shor in 1994, that factors large numbers and breaks the encryption most of the internet uses for key exchange and signatures.