The computing units of quantum computers are called quantum bits, or qubits for short. They are the counterpart to the bits in conventional computers. However, a computer bit can only have the value one or zero; it’s like an on/off switch. A qubit can have both values simultaneously. This is because the information carriers are atoms, electrons, or other objects from the microcosm, and these obey the complex rules of quantum physics.
Two phenomena of quantum physics are used for quantum computers: superposition and entanglement. Yet these quantum states are very fragile. They must be protected from external sources of disturbance such as heat or radiation; otherwise, they will break down within a short time. This leads to errors in calculations.