New Light Extractor Boosts Diamond Sensor Signals

Diamond-based quantum sensors could soon become more powerful and easier to use, thanks to a new device that dramatically boosts their light signals. Researchers have developed a nanoscale light extractor that sits on top of diamond surfaces and enhances light emission from nitrogen-vacancy centers—tiny defects in diamond that act as incredibly sensitive quantum sensors. This breakthrough addresses a fundamental : diamond's high refractive index traps most light inside, making these sensors difficult to read in practical applications.

The key finding is that this silicon-based extractor increases the optical power collected from nitrogen-vacancy centers by more than 35 times compared to unpatterned diamond surfaces. For sensors positioned just 10 nanometers below the diamond surface, the device directs light into a narrow ±30° cone that can be easily captured with standard optical systems. This enhancement persists across the entire emission spectrum of these quantum sensors, from 635 to 800 nanometers.

The researchers used an adjoint optimization to design the light extractor, essentially letting computer algorithms find the ideal structure through repeated simulations. They employed time-domain simulations that modeled how light behaves across different wavelengths simultaneously, ensuring the final design would work across the sensor's full emission range. The optimization process evolved a silicon pattern above the diamond surface, gradually shaping it to maximize light extraction while maintaining features large enough for practical fabrication using electron-beam lithography.

Simulation show remarkable performance. Figure 3(B) demonstrates extraction efficiency reaching over 35 times enhancement for sensors at 10 nanometer depths, with even higher gains for shallower positions. The device also shows impressive robustness—Figure 4 reveals it maintains good performance even when sensors are misaligned by up to 40 nanometers laterally or when fabrication errors cause edge deviations of ±20 nanometers. The far-field radiation patterns in Figure 3(D) confirm the extracted light forms a well-defined beam that stays within the target collection cone across the entire spectrum.

This advancement matters because nitrogen-vacancy centers in diamond serve as exquisitely sensitive detectors for magnetic fields, temperature, and strain at the nanoscale. They're used in quantum computing, biomedical sensing, and materials characterization, but their utility has been limited by poor light collection efficiency. The new extractor makes these sensors more practical for real applications by allowing simpler optical setups to collect significantly more signal. Unlike previous approaches that required etching the diamond—which can damage the material and degrade sensor performance—this simply places a patterned silicon layer on the surface.

Despite these advances, some limitations remain. The paper notes that the exact effects of the silicon extractor on the quantum properties of nitrogen-vacancy centers, particularly their spin coherence characteristics, are unknown and require future experimental investigation. Additionally, while the device shows good tolerance to positioning errors, optimal performance still requires careful alignment during fabrication. The researchers also acknowledge that a similar approach was recently described in a preprint by other scientists, indicating this field is rapidly evolving.