Scientists demonstrated the first entangled measurement for W states, a breakthrough for quantum information transfer and computing.
Quantum entanglement highlights the profound divide between classical and quantum physics. In this phenomenon, the state of each photon cannot be described independently, challenging the classical view that every particle has its own distinct reality—an idea that deeply troubled Einstein. Grasping the significance of entanglement is vital for advancing next-generation quantum technologies.
To build such technologies, researchers must be able to reliably generate multi-photon entangled states and accurately determine which type of state has been produced. Conventional quantum tomography, the standard method for analyzing these states, faces a major obstacle: the number of required measurements increases exponentially as the number of photons grows, creating a severe challenge for data collection.
When available, an entangled measurement makes it possible to determine the type of entangled state in a single step. Such a measurement had already been achieved for the Greenberger-Horne-Zeilinger (GHZ) entangled quantum state, but for the W state—another fundamental form of multi-photon entanglement—it had neither been theoretically proposed nor experimentally demonstrated until now.
This challenge was taken up by a team of researchers from Kyoto University and Hiroshima University, who successfully developed a new entangled measurement method capable of identifying the W state.
“More than 25 years after the initial proposal concerning the entangled measurement for GHZ states, we have finally obtained the entangled measurement for the W state as well, with genuine experimental demonstration for 3-photon W states,” says corresponding author Shigeki Takeuchi.
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