What is a physical qubit?
One actual qubit on a chip or in a trap. Physical qubits make errors, roughly once every few hundred to few thousand operations today.
When a company announces a chip with 1,000 qubits, it means physical qubits. That number says little on its own, because a qubit that makes an error every few hundred steps can’t run the millions of steps a useful algorithm needs.
The error rate matters as much as the count. Most estimates for breaking encryption assume physical qubits that fail about once per thousand operations.
Related
- Logical qubitA reliable qubit built from many physical qubits using error correction.
- Quantum error correctionMethods that protect quantum information by spreading it over many qubits and repeatedly checking for errors.
- DecoherenceThe loss of a qubit's blend through contact with its surroundings, which turns it into ordinary randomness.
- QubitThe basic unit of a quantum computer: it can be 0, 1, or a blend of both until it is measured.