Scalable creation of long-lived multipartite entanglement

TL;DR

This paper demonstrates a scalable method for creating long-lived multipartite entanglement using ion traps, achieving high-fidelity GHZ states and maintaining coherence over seconds.

Contribution

The authors present a scalable approach combining ion shuttling and laser gates to generate and preserve multipartite entanglement in a micro-structured ion trap.

Findings

Generated a four-ion GHZ state with 94.4% fidelity.

Maintained 69% coherence over 1.1 seconds using dynamic decoupling.

Implemented scalable ion shuttling and entangling operations.

Abstract

We demonstrate the deterministic generation of multipartite entanglement based on scalable methods. Four qubits are encoded in $^{40}$Ca$^+$, stored in a micro-structured segmented Paul trap. These qubits are sequentially entangled by laser-driven pairwise gate operations. Between these, the qubit register is dynamically reconfigured via ion shuttling operations, where ion crystals are separated and merged, and ions are moved in and out of a fixed laser interaction zone. A sequence consisting of three pairwise entangling gates yields a four-ion GHZ state $\vert\psi\rangle=\tfrac{1}{\sqrt{2}}\left(\vert 0000\rangle+\vert 1111\rangle\right)$, and full quantum state tomography reveals a Bell state fidelity of 94.4(3)\%. We analyze the decoherence of this state and employ dynamic decoupling on the spatially distributed constituents to maintain 69(5)\% coherence at a storage time of 1.1~seconds.