Entanglement-assisted non-local interferometry demonstrated with quantum memories
Feb 27th 2026
A team used entangled quantum memories based on silicon vacancy centres in diamond to demonstrate non-local optical interferometry that erases which-path information and non-destructively heralds photons, extending the effective baseline to 1.55 km and improving weak-signal sensitivity scaling while highlighting current rate and fidelity limits.
- Researchers used silicon vacancy centers in diamond nanophotonic cavities as two-qubit network nodes with an electron communication qubit and a 29Si nuclear memory qubit.
- The team combined photon mode erasure with non-local, non-destructive photon heralding to filter vacuum noise and imprint the differential optical phase onto entangled nuclear spins.
- Electron–electron entanglement rates reached up to 13 Hz at fidelity ≥0.5 and 1.9 Hz at F = 0.79, while nucleus–nucleus entanglement achieved F = 0.73 at 0.25 Hz using error-detection mid-circuit.
- With non-local heralding the measured nuclear two-qubit parity visibility averaged 0.090 compared with 0.031 without heralding, demonstrating improved signal visibility.
- The protocol was run with an effective baseline of up to 1.55 km, where nucleus–nucleus Bell fidelity remained 0.63 and parity visibility was 0.11.
- Non-local heralding changes the interferometer sensitivity scaling in the weak-signal regime from proportional to the square of the mean photon number to proportional to the mean photon number, but mis-heralding and imperfect Bell fidelity reduce this advantage at very low signal levels.
- Operational limits include low end-to-end data rates (overall measurement rates on the order of tens of millihertz), photon loss, detector noise and entanglement-phase noise from long fiber links.
- Authors point to clear upgrade paths—quantum repeaters, entanglement multiplexing, more qubits per station and phase-based spin–photon gates—to raise rates and reach practical long-baseline imaging and deep-space communication applications.