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W state

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description W state Overview

In quantum information science, a W state is a specific type of multipartite entangled quantum state involving three or more qubits. For three qubits, it is defined as a superposition where exactly one qubit is in the excited state while the others are in the ground state. The W state is highly notable because it retains bipartite entanglement even if one of its particles is measured or lost to the environment. This robustness against particle loss distinguishes it from the Greenberger-Horne-Zeilinger state.

help W state FAQ

What is the three-qubit W state written as?

The standard three-qubit form is (|001⟩ + |010⟩ + |100⟩)/√3. It is an equal superposition in which exactly one of the three qubits is in the |1⟩ state.

How is a W state different from a GHZ state?

A three-qubit GHZ state is commonly written as (|000⟩ + |111⟩)/√2, whereas a W state distributes one excitation among the qubits. Their entanglement also behaves differently when one qubit is lost.

Does a W state stay entangled if one qubit is measured or lost?

It can retain bipartite entanglement after one qubit is removed, which is a defining contrast with an ideal GHZ state. This robustness makes W-type entanglement interesting for quantum networking and communication.

How can a W state be created experimentally?

Researchers can prepare W states with controlled quantum gates, shared photons, trapped ions, or superconducting qubits. A gate-based circuit typically creates a single excitation and then distributes its amplitude across multiple qubits.

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