What is decoherence?
The loss of a qubit's blend through contact with its surroundings, which turns it into ordinary randomness.
Heat, stray electric and magnetic fields, and vibration all nudge a qubit, and every nudge leaks a little of its state into the environment. After enough leaks, the amplitudes no longer interfere, and the qubit behaves like a coin flip.
This is why superconducting quantum chips are cooled to about a hundredth of a degree above absolute zero, colder than outer space. Even so, their qubits keep their state for roughly a tenth of a millisecond, so a computation has to finish, or be protected by error correction, within that time.
Related
- QubitThe basic unit of a quantum computer: it can be 0, 1, or a blend of both until it is measured.
- SuperpositionA qubit state that is a blend of 0 and 1, with an amplitude for each.
- Quantum error correctionMethods that protect quantum information by spreading it over many qubits and repeatedly checking for errors.
- Physical qubitOne actual qubit on a chip or in a trap. Physical qubits make errors, roughly once every few hundred to few thousand operations today.