Kyoto and Hiroshima researchers demonstrate entangled measurement for W states

September 29, 2026 at 05:28 PM1 min

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Researchers at Kyoto University and Hiroshima University have developed and experimentally demonstrated an entangled measurement that identifies the W state, a key multi-photon entangled state. The method uses cyclic shift symmetry and a photonic quantum circuit performing a quantum Fourier transformation. The work addresses a 25-year gap since the entangled measurement for GHZ states was proposed.

Key Facts

The entangled measurement for the W state was experimentally demonstrated for 3-photon W states.
The method is based on the cyclic shift symmetry of the W state and uses a photonic quantum circuit performing a quantum Fourier transformation.
The entangled measurement for the GHZ state had been accomplished earlier, but no comparable method existed for the W state until this work.
Corresponding author Shigeki Takeuchi noted that more than 25 years after the initial proposal for GHZ entangled measurement, the W state entangled measurement has now been obtained.

Entangled Measurement Gap

Quantum tomography, the standard approach for identifying entangled states, requires exponentially more measurements as photon number increases. An entangled measurement offers a one-shot alternative, and scientists had already achieved this for the Greenberger-Horne-Zeilinger (GHZ) state. No comparable method had been proposed or experimentally demonstrated for the W state, another important type of multi-photon entanglement. Researchers at Kyoto University and Hiroshima University set out to address this missing capability.

Cyclic Shift Symmetry Method

The researchers built their approach around the W state's cyclic shift symmetry, where photon arrangement can be shifted in a repeating cycle while preserving an underlying pattern. Using this symmetry, the team theoretically developed an entangled measurement based on a photonic quantum circuit. The circuit performs a quantum Fourier transformation, a mathematical operation that reorganizes quantum information to reveal difficult-to-detect patterns. The proposed method can, in principle, be applied to W states containing any number of photons.