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arXiv:1201.0674 · Physical Review B

Efficient photon detection from color centers in a diamond optical waveguide

David Le Sage, Linh Pham, Nir Bar‐Gill, Chinmay Belthangady, Mikhail D. Lukin, Amir Yacoby, Ronald Lee Walsworth

Published Mar 23, 2012• 181 citations
arXivHTMLPDF

Abstract

A common limitation of experiments using color centers in diamond is the poor photon collection efficiency of microscope objectives due to refraction at the diamond interface. We present a simple and effective technique to detect a large fraction of photons emitted by color centers within a planar diamond sample by detecting light that is guided to the edges of the diamond via total internal reflection. We describe a prototype device using this ``side-collection'' technique, which provides a photon collection efficiency $\ensuremath{\approx}47%$ and a photon detection efficiency $\ensuremath{\approx}39%$. We apply the enhanced signal-to-noise ratio gained from side collection to ac magnetometry using ensembles of nitrogen-vacancy (NV) color centers, and demonstrate an ac magnetic field sensitivity $\ensuremath{\approx}100\phantom{\rule{0.28em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$, limited by added noise in the prototype side-collection device. Technical optimization should allow significant further improvements in photon collection and detection efficiency as well as subpicotesla NV-diamond magnetic field sensitivity using the side-collection technique.

DOI
10.1103/physrevb.85.121202

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A common limitation of experiments using color centers in diamond is the poor photon collection efficiency of microscope objectives due to refraction at the diamond interface. We present a simple and effective technique to detect a large fraction of photons emitted by color centers within a planar diamond sample by detecting light that is guided to the edges of the diamond via total internal reflection. We describe a prototype device using this ``side-collection'' technique, which provides a photon collection efficiency \ensuremath≈47\ensuremath{\approx}47%\ensuremath≈47 and a photon detection efficiency \ensuremath≈39\ensuremath{\approx}39%\ensuremath≈39. We apply the enhanced signal-to-noise ratio gained from side collection to ac magnetometry using ensembles of nitrogen-vacancy (NV) color centers, and demonstrate an ac magnetic field sensitivity \ensuremath≈100pT/Hz\ensuremath{\approx}100\phantom{\rule{0.28em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}\ensuremath≈100pT/Hz​, limited by added noise in the prototype side-collection device. Technical optimization should allow significant further improvements in photon collection and detection efficiency as well as subpicotesla NV-diamond magnetic field sensitivity using the side-collection technique.
Nitrogen-Vacancy (NV) centers in diamond have emerged as a leading platform for quantum sensing, particularly in magnetic field detection. Efficient interrogation of large NV ensembles is crucial for achieving high sensitivity. This paper presents a comprehensive analysis of the optical efficiencies that govern the performance of NV-based sensing systems, focusing on excitation, conversion, and collection, leading to a novel collection design improving upon state-of-the-art results. To optimize various excitation schemes, we developed numerical tools capable of accurately calculating excitation efficiencies for arbitrary power density distributions. Using these tools, we investigated several techniques, including reflective coatings and corner excitation, and achieved excitation efficiencies exceeding 0.7, compared to the∼0.4\sim 0.4∼0.4efficiency achieved by standard methods. We also measured the conversion efficiency of NV centers, quantifying the ratio of absorbed green excitation vs. fluorescence, in various diamond samples. This value is usually missing in the literature, and therefore important to quantify in different regimes. We obtained a value of ηv=0.22 ± 0.03, which is consistent with theoretical expectations. Furthermore, we designed and experimentally validated a novel Compound Trapezoid Collector (CTC) for enhanced photon collection. The CTC offers performance comparable to that of traditional Compound Parabolic Collectors (CPCs), but with a significantly smaller form factor and simplified manufacturing. Our prototype CTC achieved a collection efficiency of 0.33, with the potential to reach approximately∼0.8\sim 0.8∼0.8. This work provides insights into optimizing the optical efficiencies of NV-based sensing systems and contributes to the development of practical devices.
We present a design to increase the amount of collected fluorescence emitted by nitrogen-vacancy color centers in diamond used for quantum-sensing. An improvement was measured in collected fluorescence when comparing oppositely faced emitting surfaces by a factor of 3.8(1). This matches ray-tracing simulation results. This design therefore improves on the shot noise limited sensitivity in optical readout-based measurements of, for instance, magnetic and electric fields, pressure, temperature, and rotations.
The long-lived electronic spin of the nitrogen-vacancy (NV) center in diamonds is a promising quantum sensor for detecting nanoscopic magnetic and electric fields in various environments. However, the poor signal-to-noise ratio (SNR) of prevalent optical spin-readout techniques presents a critical challenge in improving measurement sensitivity. Here, we address this limitation by coupling individual NVs to optimized diamond nanopillars, thereby enhancing the collection efficiency of fluorescence. Guided by near-field optical simulations, we predict improved performance for tall (≥5 μm) pillars with tapered sidewalls. This is subsequently verified by fabricating and characterizing a representative set of structures using a newly developed nanofabrication process. We observe increased SNR for optimized devices, owing to improved emission collimation and directionality. Promisingly, these devices are compatible with low-numerical-aperture collection optics and a reduced tip radius, reducing experimental overhead and facilitating improved spatial resolution for scanning applications.
Magnetometers using ensemble nitrogen-vacancy (NV) centers are promising because of their ability to measure magnetic fields in a variety of environments. To achieve high magnetic sensitivity, high collection efficiency of the fluorescence from the NV centers is essential. Due to the high refractive index of diamond, some of the photons from NVs diffuse to the sides of the diamond substrate[1]. In this study, we propose a method to improve the light collection efficiency by polishing the sides of the 12C-enriched chemical vapor deposition (CVD) growth diamond at an angle of 30 degrees and investigating the magnetic sensitivity.
The nitrogen-vacancy (NV) color center in diamond is a promising solid-state quantum system at room temperature. However, its sensitivity is limited by its low fluorescence collection efficiency, and its coherence time is limited by spin interference of impurity electrons around the NV color center. Here, we innovatively fabricated a one-dimensional photonic crystal on the surface of diamond, which greatly improved the fluorescence intensity of the NV color centers and increased the sensitivity of NV ensembles by a factor of 2.92. In addition, the laser reflected by the photonic crystal excites impurity electrons around the NV color centers, improving the electric field environment around the NV color centers, which exponentially prolongs the dephasing time (from 209 to 841 ns), opening avenues for NV color-center ensemble sensors.
A single nitrogen-vacancy (NV) center in diamond is utilized to perform nanoscale magnetic measurements. However, the low contrast and poor collection efficiency of spin-dependent emitted photons limited the instrument sensitivity to approximately several nT/Hz. Here, we design a diamond magnetometer based on a chiral waveguide. We numerically demonstrate that the proposed device achieves a sensitivity of 170 pT/Hz owing to near-unity contrast and efficient photon collection. We also confirm that the device sensitivity is robust against position misalignment and dipole misorientation of an NV center. The proposed approach will enable the construction of a highly-sensitive magnetometer with high spatial resolution.