An illustration of quantum communication. Photo: VCG

China Mobile researchers have created high-dimensional multipartite entangled states on a silicon photonic quantum chip, setting what the telecom company said is a new scale record in the field and offering a new approach to a key challenge in expanding high-dimensional quantum systems, the Global Times learned on Monday.

The China Mobile research team produced both three-party, four-dimensional GHZ and W entangled states, with fidelities of 93.2 percent and 90.1 percent, respectively. The company said the experiment marked the largest scale achieved so far for high-dimensional multipartite entanglement and that the approach could be extended to larger systems.

"The advance not only strengthens the theoretical foundation for high-dimensional quantum entanglement, but also helps overcome a key bottleneck in scaling up its preparation, laying the groundwork for broader applications in quantum communications, quantum computing and precision measurement," a company statement said.

Quantum entanglement is a core resource in quantum technology, enabling capabilities that go beyond the limits of classical physics. Research has long focused largely on generating entangled states in two-dimensional quantum systems, or qubits, even though quantum processes can involve higher dimensions.

A conventional qubit has two basic states, usually represented as 0 and 1. A high-dimensional quantum information unit can have more. A four-dimensional unit, for example, has four basic states - 0, 1, 2 and 3.

Compared with conventional two-dimensional quantum entanglement, high-dimensional entangled states can carry more information, offer greater resistance to noise and improve the stability and accuracy of quantum information transmission. They can also simplify quantum-computing circuits and boost computing efficiency.

As part of the latest work, the team proposed what the company described as the first universal definition of high-dimensional W entangled states, further developing the theoretical framework for high-dimensional quantum entanglement. The definition can be applied to different numbers and dimensions of quantum information units, providing a theoretical basis for designing larger high-dimensional W states.

Building on that theoretical work, the team developed a scalable method for producing high-dimensional quantum entangled states by exploiting the multiple states available to a single photon and using delayed quantum measurements.

By sequentially manipulating and measuring different distinguishable states of photons, the approach allows a single photon to carry multiple quantum information units. According to the company, this preserves quantum entanglement while reducing the difficulty of scaling up the system, helping overcome the scale limitations of conventional preparation methods.

To demonstrate the feasibility of the approach, the researchers conducted an experiment on a programmable silicon photonic quantum chip measuring 16 millimeters by 1.5 millimeters.

In the experiment, one photon carried two quantum information units, while another carried a third. Each of the three units had four basic states, together forming a three-party, four-dimensional quantum system. The team successfully generated both GHZ and W entangled states, setting what the company described as a new scale record for high-dimensional multipartite entanglement.

The company said the approach can be efficiently extended to larger systems. The research establishes a method spanning the theoretical design and chip-based generation of high-dimensional quantum entangled states, laying a foundation for developing larger and higher-performance quantum systems.

China Mobile said it would next use its programmable experimental platform to further explore applications of high-dimensional quantum technology in quantum communications, quantum computing and precision measurement.