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.
Pursuing entangled measurement for W states
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.
The researchers based their approach on the W state’s cyclic shift symmetry and introduced a theoretical method to build an entangled measurement using a photonic quantum circuit that performs quantum Fourier transformation for W states of any photon number.
To validate the method, they constructed a device designed for three photons, employing highly stable optical quantum circuits that could operate for long periods without active control. By sending in three single photons prepared with specific polarization states, the device successfully distinguished different types of three-photon W states, each tied to a unique non-classical correlation among the input photons. The team also assessed the fidelity of the entangled measurement, defined as the likelihood of obtaining the correct outcome when provided with a pure W-state input.
Future applications in quantum technologies
This achievement opens the door for quantum teleportation, or the transfer of quantum information. It could also lead to new quantum communication protocols, the transfer of multi-photon quantum entangled states, and new methods for measurement-based quantum computing.
“In order to accelerate the research and development of quantum technologies, it is crucial to deepen our understanding of basic concepts to come up with innovative ideas,” says Takeuchi.
In the future, the team aims to apply their method to a larger-scale, more general multi-photon quantum entangled state, and plans to develop on-chip photonic quantum circuits for entangled measurements.
Reference: “Entangled measurement for W states” by Geobae Park, Holger F. Hofmann, Ryo Okamoto and Shigeki Takeuchi, 12 September 2025, Science Advances.
DOI: 10.1126/sciadv.adx4180
Funding: Japan Science and Technology Agency, Japan Society for the Promotion of Science
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5 Comments
For the W state—another fundamental form of multi-photon entanglement—it had neither been theoretically proposed nor experimentally demonstrated until now.
very good!
Topological Vortex Theory (TVT) proves that symmetry is an inevitable requirement of spacetime topology, and any apparent violation arises from observational limitations or model defects. The value of science lies in revealing truth rather than maintaining dogma. Only by adhering to the universality of symmetry and deepening our understanding of the nature of spacetime through theories like Topological Vortex Theory can physics avoid the trap of pseudoscience and return to a symmetry-dominated research paradigm; otherwise, it will sink completely into the mire of self-denial.
The harm caused by CP violation theory to physics research: misguiding antimatter exploration, mythologizing imaginary particle concepts, and hindering scientific paradigm shifts. Scientific development and progress requirement a return to symmetry-dominated scientific rationality and the rejection of pseudoscientific constructs.
If researchers are truly interested in science, please visit https://zhuanlan.zhihu.com/p/1952302320672043229.
Was in the chat!
In today’s physics, some so-called peer-reviewed journals—including Physical Review Letters, PNAS, Nature, Science, and others—stubbornly insist on and promote the following:
1. Even though θ and τ particles exhibit differences in experiments, physics can claim they are the same particle. This is science.
2. Even though topological vortices and antivortices have identical structures and opposite rotational directions, physics can define their structures and directions as entirely different. This is science.
3. Even though two sets of cobalt-60 rotate in opposite directions and experiments reveal asymmetry, physics can still define them as mirror images of each other. This is science.
4. Even though vortex structures are ubiquitous—from cosmic accretion disks to particle spins—physics must insist that vortex structures do not exist and require verification. Only the particles that like God, Demonic, or Angelic are the most fundamental structures of the universe. This is science.
5. Even though everything occupies space and maintains its existence in time, physics must still debate and insist on whether space exists and whether time is a figment of the human mind. This is science.
6. Even though space, with its non-stick, incompressible, and isotropic characteristics, provides a solid foundation for the development of physics, physics must still insist that the ideal fluid properties of space do not exist. This is science.
and go on.
What are the shames?
Is this the counterintuitive science they widely promote? Fortunately, not every member of the public is gullible. Topology is reconfiguring the cognitive framework of modern civilization. With the gradual refinement of artificial intelligence (AI), we are no longer entirely reliant on mediated deception by some so-called peer-reviewed publications (including Physical Review Letters, Science, Nature, etc.). We now possess the means to leverage AI’s efficiency to enhance scientific rigor and productivity.
If researchers are interested, please visit https://zhuanlan.zhihu.com/p/1954126217461602098 (If the link is available).