Six vibration modes entangled on one chip, in a Shenzhen lab

At the International Quantum Academy in Shenzhen, Tan Dian's group has entangled up to six phonon modes on a single chip, and moved some of those states from one acoustic resonator to another. Entanglement is the strange link between quantum objects that keeps their correlations intact even when the parts are treated separately. Here the objects are vibrations inside a solid, which is what makes the result unusual.

The team used high-overtone bulk acoustic wave resonators, called HBARs, which support many long-lived vibration modes and can be integrated on chips. Earlier setups often relied on three-dimensional microwave cavities. Here the researchers put two HBARs, superconducting qubits and a tunable coupler on one two-dimensional hybrid chip. By tuning the spacing of the acoustic mode frequencies and the qubit-phonon coupling, a single qubit could couple strongly to several mechanical modes. The paper reports genuinely multipartite entangled states of two, four and six modes, with fidelities of 0.912, 0.790 and 0.570. Tan explained that genuine entanglement means the correlations are shared by the whole multimode system and cannot be split into smaller, independent entangled pieces. The steady fall in fidelity as the number of modes grows shows how quickly the task gets harder.

Transfer is the second half of the result. Two-mode and four-mode states moved between the two resonators with fidelities of 0.785 and 0.601. To check the states, the group built a tomography method, a way of reconstructing a quantum state from measurements, that reuses a limited number of qubits across modes and needs only two superconducting qubits. The team says this is the largest experimental characterization of a multimode phonon state on a quantum acoustics platform so far.

What changes for a reader? For now, nothing outside the lab. The researchers also propose an architecture that couples more qubits to more resonators through controllable couplers, with the long-term aim of modular phonon-based quantum networks. Those networks would be built from separate nodes linked by vibration-borne quantum states, and the paper does not give a timeline or a device that could be built on that basis. The result is a demonstration that the components can work together, and the falling fidelities mark the gap that remains before the approach could scale.

The work involves several institutions beyond the academy, including Southern University of Science and Technology, the Shenzhen branch of Hefei National Laboratory, Zhejiang University and Jimei University, and collaborators at the University of Stuttgart and EPFL.