What Is a Qubit?
How a qubit differs from a bit, and what physical systems can act as one.
Qubits
What is qubits?
A qubit is a two-level quantum system used as the basic unit of quantum information.
Qubits are described by amplitudes for the outcomes 0 and 1 rather than by a definite value.
They can be realised with superconducting circuits, trapped ions, neutral atoms, photons, and spins.
Recommended learning sequence
- What Is a Qubit?How a qubit differs from a bit, and what physical systems can act as one.
Frequently asked questions
- How is a qubit different from a bit?
- A bit is definitely 0 or 1. A qubit carries amplitudes for both outcomes that can interfere, and measuring it returns one outcome at random with probabilities set by those amplitudes.
Lessons in this topic
Related subjects
Superposition
Superposition is a quantum state formed by combining other states, each carrying an amplitude.
Quantum Hardware
Quantum hardware comprises the physical systems and control electronics that implement and manipulate qubits.
Quantum Measurement
Measurement extracts a definite classical outcome from a quantum system, with probabilities given by squared amplitudes.