Plate Nº 93 · recorded October 9, 2026
PhysicsReported finding
New superconducting fusion method entangles 13 microwave photons
Tsinghua researchers demonstrated deterministic fusion of microwave photons into a graph state with 13 entangled qubits, a step toward larger photonic networks for quantum computing.
By James Calloway3 min read697 words
In brief
- Demonstrated genuine multipartite entanglement across 13 photonic qubits
- Published in Nature Physics on October 9, 2026; DOI 10.1038/s41567-026-03471-5
- Conducted by Tsinghua University and Hefei National Laboratory; lead author Yan Li, co-senior author Hongyi Zhang
- Fusion method is deterministic, programmable, and nondestructive, using parity measurements on microwave photons
- Researchers plan multidetector architectures to scale to larger, higher-dimensional graph states
Researchers at Tsinghua University and Hefei National Laboratory have demonstrated a way to deterministically link small groups of microwave photons into larger entangled states, achieving genuine multipartite entanglement across 13 photonic qubits in a paper published in Nature Physics on October 9, 2026.
Qubits are the quantum equivalent of computer bits. They store and process information by exploiting quantum mechanics, allowing certain calculations that ordinary computers cannot easily perform. Entanglement, the property at the heart of the new work, links particles so that their shared state cannot be described as separate, independent states.
Photons are elementary particles of light; microwave photons occupy a specific, lower-energy band of the electromagnetic spectrum. Superconducting circuits naturally emit and detect microwave photons, which makes them a convenient match for the new experiment.
The new work centers on "graph states," a particular kind of entanglement whose connections resemble a mathematical network. Each qubit acts like a node; the "edges" between them define how the entanglement is shared. These structures serve as key resources for quantum communication, quantum networks, and measurement-based quantum computing.
What problem does the team solve?
Building large graph states has been difficult. Conventional methods use optical components like mirrors and beam splitters to perform an operation called fusion, which joins smaller entangled groups into a bigger one. These approaches are probabilistic—many attempts simply fail.
"A promising way to build them is 'fusion': rather than making one very large, entangled state in a single step, one connects smaller resource states together," co-senior author Hongyi Zhang said. "The difficulty is that conventional fusion methods are probabilistic, so many attempts fail and the resource overhead grows rapidly."
The team asked whether fusion could be made deterministic—always succeeding—through a different measurement approach.
How does the new fusion method work?
The researchers used a superconducting circuit—a chip-like device made from a material that conducts electricity with zero resistance at very low temperatures—to generate small entangled states of microwave photons.
A "quantum non-demolition detector" then performed a parity measurement on selected photon pairs. Parity measurement simply checks whether a group contains an even or odd number of photons, without absorbing or destroying them. The act of measuring entangles the pairs while leaving the photons intact, so they remain usable for further operations.
Frequency tuning then selects which photons to fuse. "We use superconducting circuits to generate microwave photons in small, entangled states," Zhang explained. "A quantum non-demolition detector then performs a parity measurement on selected photon pairs, entangling them without destroying them and thereby connecting the two smaller graph states into a larger one."
The resulting scheme is:
- Deterministic (always succeeds, unlike probabilistic methods)
- Programmable (which qubits connect can be adjusted)
- Nondestructive (photons remain available for further operations)
What did the team actually demonstrate?
In their initial test, the team created graph states in which connections between qubits can be reconfigured after fabrication. They showed genuine multipartite entanglement across 13 photonic qubits—meaning the entanglement spanned the entire group rather than being confined to smaller, separate clusters.
"Our main contribution is a fusion operation that is deterministic, programmable and nondestructive," Zhang said. "More broadly, the work offers an architecture for scaling photonic graph states by connecting smaller, on-demand resource states."
Why does this matter for quantum computing?
Larger, more connected graph states matter for several applications:
- Measurement-based quantum computing, which uses entangled states as the primary computational resource
- Quantum networking, where distant nodes share entanglement
- Quantum error-correction schemes, where redundancy and connectivity protect information
The approach joins smaller building blocks instead of generating one large state in a single, uninterrupted process. That modularity could prove essential as researchers try to assemble ever-larger quantum systems.
What's next?
The team has clear plans for follow-ups. "Next, we will improve the device fidelity, photon-generation efficiency and detector performance," Zhang added. "We also plan to develop multidetector architectures that can perform more fusion operations and generate larger, higher-dimensional graph states."
The paper appeared as Yan Li et al, "Deterministic and programmable fusion for the scalable generation of photonic graph states," Nature Physics (2026). DOI: 10.1038/s41567-026-03471-5.
via Phys.org Physics (Source)
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