Hybrid diamond chip strengthens interactions between light and quantum bits

Introduction

A recent study demonstrates a hybrid nanophotonic platform that integrates gallium phosphide (GaP) photonic structures with a diamond substrate hosting silicon‑vacancy (SiV) centers. By refining a stamp‑transfer fabrication method, the researchers produced over 600 GaP cavities with a 99.5 % yield and achieved above‑unity cooperativity—strong, deterministic interactions between light and the SiV spin qubits. This breakthrough addresses a long‑standing bottleneck in quantum networking: efficiently converting stationary qubit states into traveling photons.

Hybrid Design and Scalable Fabrication

The platform leverages two complementary materials:

• Diamond provides a pristine host for SiV centers, preserving their long spin‑relaxation times and narrow optical transitions.
• GaP offers a high refractive index and strong nonlinearities, enabling on‑chip waveguides, switches, and frequency converters.

A key innovation is a scalable stamp‑transfer process that moves patterned GaP membranes onto unetched diamond without damaging the crystal lattice. Iterative optimization raised the transfer yield to nearly 100 % and allowed precise alignment of the photonic mode with the SiV emitters, overcoming the spatial separation that previously limited cooperativity.

Demonstrated Performance

Optical spectroscopy of the transferred cavities confirmed the desired resonant properties. When probed with a laser at cryogenic temperatures (4 K), the devices exhibited:

• Above‑unity cooperativity, meaning the photon‑SiV interaction is strong enough for deterministic spin readout.
• Spin‑relaxation times >0.4 ms, supporting single‑shot electron‑spin measurements.
• Distinct spectral signatures for each spin state, enabling real‑time monitoring of qubit dynamics.

These metrics collectively demonstrate that the SiV‑photon coupling is reliable and repeatable across the large array of fabricated devices.

Implications for Quantum Networks and Beyond

Achieving high cooperativity on a scalable chip opens several pathways:

1. Quantum communication – Integrated waveguides and modulators can route photons from SiV nodes into fiber‑optic links, forming the backbone of a quantum internet.
2. On‑chip quantum processing – Multiple SiV qubits could be interconnected on a single GaP‑diamond wafer, allowing local entanglement and gate operations without external bulk optics.
3. Material versatility – The stamp‑transfer approach can be adapted to other quantum emitters (e.g., silicon‑carbide defects or 2D‑material excitons), broadening the toolbox for scalable quantum hardware.

Future work will focus on linking several GaP‑on‑diamond devices on the same chip to demonstrate entanglement between distant SiV qubits, and on further refining the fabrication steps to push cooperativity even higher. If these goals are met, the hybrid platform could become a cornerstone for practical quantum communication, secure cryptography, and distributed quantum computing.

--- The article is based on a peer‑reviewed report in Optica Quantum and reflects the authors' findings without adding speculative claims.