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SWAP gate

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description SWAP gate Overview

The SWAP gate is a fundamental component in quantum circuits. It facilitates the exchange of quantum information between pairs of qubits, regardless of their initial entanglement state. This capability is crucial for implementing complex quantum algorithms and correcting errors within quantum computations. Primarily used by researchers and developers working with two-qubit systems exploring quantum routing and manipulation of entangled states.

help SWAP gate FAQ

What does a SWAP gate do to two qubits?

It exchanges their complete quantum states: an input written as |a,b⟩ becomes |b,a⟩. The operation does not clone either state, so it does not violate the no-cloning theorem.

How many CNOT gates are needed to build a SWAP gate?

The standard decomposition uses three CNOT gates with alternating control and target directions. This makes SWAP relatively costly on hardware where every two-qubit gate adds noise.

Why do quantum computers need SWAP gates if qubits are addressable?

Many processors permit two-qubit operations only between physically connected neighbors. A compiler inserts SWAPs to route logical qubit states across coupling maps used by devices from IBM, Google, and other hardware developers.

Does a SWAP gate create entanglement?

A SWAP gate alone does not create entanglement from two separable input states; it only exchanges them. The related square-root-of-SWAP gate can act as an entangling operation and appears naturally in exchange-coupled qubit systems.

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