Broadband Magnetometry and Temperature Sensing with a Light Trapping Diamond Waveguide (1406.5235v1)

Abstract: Solid-state quantum sensors are attracting wide interest because of their exceptional sensitivity at room temperature. In particular, the spin properties of individual nitrogen vacancy (NV) color centers in diamond make it an outstanding nanoscale sensor of magnetic fields, electric fields, and temperature, under ambient conditions. Recent work on ensemble NV-based magnetometers, inertial sensors, and clocks have employed $N$ unentangled color centers to realize a factor of up to $\sqrt{N}$ improvement in sensitivity. However, to realize fully this signal enhancement, new techniques are required to excite efficiently and to collect fluorescence from large NV ensembles. Here, we introduce a light-trapping diamond waveguide (LTDW) geometry that enables both high fluorescence collection ($\sim20\%$) and efficient pump absorption achieving an effective path length exceeding $1$ meter in a millimeter-sized device. The LTDW enables in excess of $2\%$ conversion efficiency of pump photons into optically detected magnetic resonance (ODMR) fluorescence, a \textit{three orders of magnitude} improvement over previous single-pass geometries. This dramatic enhancement of ODMR signal enables broadband measurements of magnetic field and temperature at less than $1$ Hz, a frequency range inaccessible by dynamical decoupling techniques. We demonstrate $\sim 1~\mbox{nT}/\sqrt{\mbox{Hz}}$ magnetic field sensitivity for $0.1$ Hz to $10$ Hz and a thermal sensitivity of $\sim 400 ~\mu\mbox{K}/\sqrt{\mbox{Hz}}$ and estimate a spin projection limit at $\sim 0.36$ fT/$\sqrt{\mbox{Hz}}$ and $\sim 139~\mbox{pK}/\sqrt{\mbox{Hz}}$, respectively.

• The paper introduces a novel light trapping diamond waveguide that improves NV sensor fluorescence collection by 1000-fold for enhanced magnetic and temperature sensing.
• Using total internal reflection, the design increases the excitation beam path within diamond to achieve 20% fluorescence collection and 1 nT/√Hz magnetic sensitivity.
• These advances enable practical applications in biomedical imaging and environmental monitoring while operating under ambient conditions without cryogenics.

An Analysis of Broadband Magnetometry and Temperature Sensing via Light Trapping Diamond Waveguides

The paper presents a significant advancement in solid-state quantum sensing, specifically focusing on the application of nitrogen vacancy (NV) centers in diamond for magnetic field and temperature sensing at ambient conditions. The researchers introduce a novel light-trapping diamond waveguide (LTDW) that enhances the efficiency of fluorescence collection and pump absorption in NV-based sensors, achieving efficiencies that surpass previous single-pass methodologies by three orders of magnitude.

Key Innovations and Results

The critical innovation detailed in the paper is the introduction of the LTDW geometry, which leverages total internal reflection to enhance the path length of the excitation beam within the diamond. This design improvement enables more thorough interaction with NV centers, which are renowned for their spin properties conducive to high sensitivity magnetic and temperature measurements.

Numerical Results:

• Fluorescence Collection: The LTDW achieves approximately 20% fluorescence collection efficiency and an over 2% conversion efficiency of pump photons into optically detected magnetic resonance (ODMR) fluorescence.
• Sensitivity: The device demonstrates a magnetic field sensitivity of around 1 nT/√Hz at frequencies between 0.1 Hz and 10 Hz, and a thermal sensitivity of about 400 µK/√Hz. Moreover, estimates suggest a spin projection limit at approximately 0.36 fT/√Hz for magnetic field and 139 pK/√Hz for temperature.
• Performance Enhancement: The LTDW showcases a ∼1000-fold improvement in ODMR signal conversion efficiency compared to traditional setups.

Practical and Theoretical Implications

The paper delineates several practical applications for the LTDW, particularly in fields requiring precision in low-frequency magnetic sensing, such as magnetocardiography and geomagnetic monitoring. Additionally, its suitability for temperature monitoring opens potential avenues in medical diagnostics and environmental sensing.

Theoretical Implications: The LTDW sets a precedent in the field of quantum sensing by enabling superior sensitivity without necessitating cryogenic environments. This not only showcases the potential for NV centers to revolutionize precision measurement technologies but also pushes the boundary of what these sensors can achieve in ambient settings.

Future Directions: Enhancements in LTDW could focus on refining collection efficiency through better geometrical configurations and surface polishing techniques, potentially incorporating chaotic path excitation to achieve a more uniform NV center excitation. Furthermore, multiplexing capabilities could expand its functionalities across various parameters beyond magnetic field and temperature.

Conclusion

The paper presents a comprehensive approach to improving NV-based quantum sensors using an innovative LTDW geometry. By drastically enhancing the fluorescence conversion efficiency, the research not only propels the sensitivity and range of these sensors but also establishes a foundation for further exploration into solid-state sensor applications spanning various scientific and technological domains. The implications for fields such as quantum information science, biomedical technology, and environmental monitoring underline the importance of these advancements, promising a significant impact on future precision sensor development.