Definition
Quantum Computer
A quantum computer is a computational device that manipulates information encoded in the quantum states of a physical system. Its operation consists of three stages:
- Initialisation: The quantum register is prepared in a predefined start state, typically a computational basis state such as .
- Evolution: The state evolves by applying a sequence of quantum operations (quantum gates) specified in advance as a quantum algorithm. These operations are represented by unitary transformations acting on the quantum register.
- Measurement: At the end of the computation, information is extracted by measuring parts of the quantum register, yielding classical outcomes probabilistically according to the quantum mechanical postulates.
Components
Quantum Register
A collection of qubits that holds the quantum state of the computer. The state space is the tensor product of the individual qubit state spaces.
Quantum Gates
Unitary operators that transform the quantum state. Common gates include the Hadamard gate, Pauli gates, and CNOT gate.
Quantum Algorithm
A predetermined sequence of quantum gates that implements a computational task, designed to exploit quantum phenomena such as superposition and entanglement.