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What is a quantum circuit?
A quantum circuit is a quantum program made of gates applied to qubits in order, followed by measurements.
Quantum circuits are usually drawn with a horizontal line per qubit and gate boxes placed on those lines from left to right. Qiskit, Cirq, PennyLane and similar libraries let you build the circuit in code and run it on a simulator or real hardware.
The circuit’s depth (how many layers of gates follow one another) and its number of two-qubit gates are the most important factors for how reliable the result is on today’s noisy hardware.
Try it yourself
The lesson Bits and qubits: the smallest piece of information lets you try this concept in the browser, with no installation.
Related packages
Related concepts
- Quantum gate · A quantum gate is a basic operation that reversibly changes the state of one or more qubits; quantum programs are sequences of gates.
- Qiskit · Qiskit is IBM’s open-source Python library for quantum programming; it lets you build circuits, run them on simulators and send them to IBM quantum computers.
- NISQ (noisy intermediate-scale quantum) · NISQ is the current era of quantum computing, named by John Preskill in 2018: devices with tens to a few hundred noisy qubits and no error correction.