Key Findings
Researchers at the University of Oxford have successfully generated multipartite entangled states across separate trapped-ion modules using a heterogeneous network of two distinct atomic elements: strontium (88 Sr+) and calcium (43 Ca+). The team achieved 4-qubit Greenberger-Horne-Zeilinger (GHZ) states across macroscopic distances and stored this distributed entanglement in calcium memory qubits for more than 10 seconds (τ = 14 ± 4 s).
Technical Details
The network architecture utilizes microfabricated surface-electrode Paul traps at each node, co-trapping one 88 Sr+ ion as an optical network interface and one 43 Ca+ ion as a hyperfine ground memory qubit. The process operates as follows:
- Entanglement Generation: Strontium ions spontaneously emit photons at 422 nm, which interfere at a central heralding station to create remote matter-matter entanglement.
- State Transfer: Local 402-nm Raman laser pulses drive geometric phase gates and error-detected iSWAP operations to transfer the entangled state from the strontium interface to the calcium memory qubits.
- Storage Performance: The 43 Ca+ ground hyperfine manifold exhibits first-order magnetic field insensitivity at 0.5 mT, which is approximately two orders of magnitude lower than that of strontium.
Background & Context
In standard trapped-ion quantum networks, using a single atomic species for both photonic coupling and quantum storage presents a technical trade-off. The laser pulses and photon emissions necessary for networking typically induce resonant light scattering and decoherence in nearby memory qubits. By employing a mixed-species approach, the Oxford team isolated the networking functions (strontium) from the storage functions (calcium).
Significance & Outlook
The ability to preserve remote entanglement for over 10 seconds represents a significant improvement over the average entanglement generation time of approximately 100 ms. By extending entanglement lifetimes by more than 100x relative to creation time, this research clears a major hurdle for the development of distributed quantum computing and quantum sensing networks.
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