A qubit is not 0 or 1 but any point on a sphere
It holds a blend of both until you measure it, when the angle decides the odds of 0 or 1.
Computerphile · Quantum Machine Learning - ComputerphileA qubit is not 0 or 1 but any point on the surface of a sphere. A classical bit is an arrow that points only straight up for 1 or straight down for 0, while a qubit is an arrow that can point anywhere on that sphere, called the Bloch sphere.
When it points between up and down, it holds a blend of both at once, what physicists call superposition. That blend gives a first kind of parallelism, because one state can represent a combination of 0 and 1, but on its own it is not enough for a quantum advantage.
The blend lasts only until the qubit is measured. Then it falls to 0 or 1, with the odds set by the angle at which it was pointing. So although the sphere holds endless possible directions, each measurement returns just one ordinary bit.
Questions people ask
If a qubit can point anywhere, can it store unlimited information?
No. You can aim the arrow in endless directions, but each measurement gives back only a 0 or a 1. The extra detail in the exact direction does not come back out as readable data.
What sets the odds of getting 0 or 1?
The angle of the arrow before measurement. The chance of each outcome is set by that angle, so different directions give different odds. You cannot predict a single result, only the chances over many tries.
Do qubits like this actually exist in real machines?
Yes. Labs build working qubits that can be placed in these in-between directions. The challenge is keeping the direction steady long enough to use it.