Nanophotonics Boost Quantum Emitter Links on a Chip

Key Takeaways

• Forward‑designed SPP platform yields 0.493 concurrence.
• Enables both energy funneling and suppression on chip.
• Works with NV‑center emitters at 670 nm wavelength.
• Scalable to three‑emitter configurations with enhanced coupling.
• Overcomes limits of photonic crystals and waveguides.

Summary

Researchers at the University of Southern Denmark and collaborators have unveiled an integrated nanophotonic platform that uses surface‑plasmon‑polariton (SPP) interference to mediate long‑range interactions between solid‑state quantum emitters on a chip. The design achieves a peak concurrence of 0.493, approaching the transient theoretical maximum, and can both enhance and suppress energy transfer between emitters. Experimental tests with nitrogen‑vacancy centers in nanodiamonds confirmed substantial modulation of transfer rates, while simulations predict scalable entanglement in two‑ and three‑emitter configurations. This forward‑designed architecture offers a compact alternative to photonic crystals, waveguides, and metasurfaces for on‑chip quantum networking.

Pulse Analysis

Quantum photonics has long wrestled with the trade‑off between integration density and coherent qubit coupling. Conventional dielectric waveguides and photonic crystals provide low‑loss channels but restrict interaction range and demand intricate fabrication. Surface‑plasmon‑polaritons, by contrast, confine light to sub‑wavelength scales on metal surfaces, granting designers unprecedented flexibility to sculpt electromagnetic fields. The new platform leverages this property, employing holographic nanostructures that shape SPP interference patterns to either concentrate or inhibit energy transfer between emitters, a capability rarely achieved in solid‑state systems.

In the experimental demonstration, nitrogen‑vacancy centers in nanodiamonds were positioned a few tens of nanometres above a silver‑silica substrate patterned with elliptic and hyperbolic nanostructures. Time‑resolved measurements revealed transfer‑rate modifications that align with finite‑difference time‑domain simulations, while master‑equation modelling predicted a concurrence of 0.493 for emitters separated by several micrometres. Extending the geometry to three emitters amplified the funneling effect, confirming that the SPP‑mediated coupling scales beyond simple pairwise interactions. These results validate a design paradigm where entanglement can be engineered on demand, rather than emerging as a stochastic by‑product.

For the quantum‑technology industry, this breakthrough translates into a practical route toward densely packed, reconfigurable qubit arrays. By sidestepping the fabrication complexity of photonic crystals and offering both enhancement and suppression modes, the platform can support error‑corrected quantum processors and multiplexed quantum‑communication links. Remaining challenges include managing metal‑induced losses and integrating active control electronics, but the demonstrated scalability and room‑temperature operation position SPP‑based nanophotonics as a compelling candidate for next‑generation quantum hardware.