Cavity-Enhanced Photon Emission from a Single Germanium-Vacancy Center in a Diamond Membrane
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-06-05 |
| Journal | Physical Review Applied |
| Authors | Rasmus HĂžy Jensen, Erika Janitz, Yannik Fontana, He Yi, Olivier Gobron |
| Institutions | Harvard University, McGill University |
| Citations | 33 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the successful coupling of a single Germanium-Vacancy (GeV) center in a diamond membrane to a high-finesse open Fabry-PĂ©rot microcavity, establishing a promising platform for efficient quantum light-matter interfaces.
- Core Achievement: A 31±15-fold increase in the spectral density of the Zero Phonon Line (ZPL) emission was achieved by coupling the GeV center to a cavity mode.
- Cavity Performance: The system demonstrated high quality, supporting âdiamond-likeâ resonances with a finesse (F) of 11,200 ± 1,700 in a micron-thick (862 nm) diamond membrane.
- GeV Superiority: The GeV center was confirmed to have superior optical properties compared to the Nitrogen-Vacancy (NV) center, including a high ZPL fraction (60-70%) and a quantum efficiency of 17±3%.
- Emission Dynamics: Analysis revealed the presence of a power-dependent dark state, which limits room-temperature photon counts but provides new insights into GeV emission dynamics.
- Cryogenic Potential: Under projected cryogenic operation, the system is predicted to achieve a Purcell enhancement (FP) of 32±16, leading to a 20±10-times reduction in excited state lifetime and > 95% of photons emitted into the ZPL.
- Platform Flexibility: The open-cavity design offers in-situ tunability and accommodates high-quality, bulk-like diamond membranes, mitigating spectral diffusion issues common in nanofabricated devices.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Cavity Finesse (F) | 11,200 ± 1,700 | Dimensionless | Measured at 603 nm (ZPL). |
| ZPL Spectral Density Enhancement | 31 ± 15 | Fold increase | Compared to free-space confocal measurements. |
| Diamond Membrane Thickness (ta) | 862 ± 4 | nm | Van der Waals bonded to the flat mirror. |
| Zero Phonon Line (ZPL) Wavelength | 603 | nm | Characteristic emission of GeV center. |
| Excitation Wavelength | 532 | nm | Used for pumping the GeV center. |
| GeV Excited State Lifetime (Ï) | 6.0 ± 0.1 | ns | Measured in confocal configuration. |
| GeV Quantum Efficiency (QE) | 17 ± 3 | % | Calculated total emission rate at saturation. |
| ZPL Fraction (Bulk GeV) | 60 - 70 | % | Significantly higher than NV centers (3%). |
| Saturation Power (Psat) - Confocal | 3.9 ± 0.3 | mW | Free-space measurement. |
| Saturation Power (Psat) - Cavity | 3.1 ± 0.5 | mW | Coupled to m=15 longitudinal mode. |
| Predicted Cryogenic Purcell Factor (FP) | 32 ± 16 | Dimensionless | Based on room-temperature parameters and Debye-Waller factor (0.6). |
| Mirror Transmission (Tflat = Tfiber) | 70 | ppm | Optimized at 603 nm. |
| Fiber Mirror Radius of Curvature (R) | 43.1 ± 0.6 | ”m | Machined via laser ablation. |
Key Methodologies
Section titled âKey Methodologiesâ- Diamond Membrane Integration: A diamond membrane containing GeV centers was prepared and Van der Waals bonded to a macroscopic flat mirror coated with a dielectric Bragg stack (low-index terminated).
- Microcavity Assembly: The cavity was completed using a microscopic spherical fiber mirror (R â 43.1 ”m, high-index terminated Bragg stack) mounted on a piezoelectric scanner for fine length tuning.
- Confocal Emitter Mapping: Emitters were excited through the back of the flat mirror (532 nm) and emission (600-605 nm) was collected via a high-NA objective (100x) to map GeV locations and confirm single-defect operation (g(2)(0) less than 0.5).
- Population Dynamics Modeling: The second-order correlation function (g(2)(Ï)) was measured across varying excitation powers and fitted using a three-level model to characterize the power-dependent shelving state (dark state).
- Cavity Resonance Tuning: The cavity length (L) was scanned using the piezoelectric stage to bring the m=15 longitudinal mode into resonance with the GeV ZPL (603 nm).
- Saturation Rate Comparison: Fluorescence count rates were measured as a function of pump power (P) in both confocal and cavity configurations. The data was fitted to extract the corrected saturating fluorescence rates (Iâ) and calculate the cavity coupling efficiency (ÎČexp = 0.40±0.13%).
- Finesse Measurement: Cavity finesse was determined by measuring broadband cavity transmission as a function of cavity length and numerically fitting the longitudinal and transverse modes.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology is foundational for next-generation quantum hardware, leveraging the superior optical properties of Group-IV defects in diamond.
- Quantum Information Processing (QIP): Provides a high-fidelity spin-photon interface, essential for building robust quantum registers and performing photon-mediated interactions between solid-state qubits.
- Quantum Networks and Repeaters: The high efficiency and spectral stability of the GeV-cavity system are critical for generating near-indistinguishable photons, enabling high-rate entanglement distribution over long-distance quantum networks.
- Deterministic Single-Photon Sources (SPS): The predicted high Purcell enhancement (> 95% ZPL emission) at cryogenic temperatures allows for the creation of highly efficient, on-demand SPS devices, crucial for linear optical quantum computing.
- Advanced Defect Engineering: The open-cavity platform serves as a flexible testbed for characterizing novel, heavier Group-IV defects (e.g., SnV, PbV) which are expected to offer longer spin coherence times than GeV or SiV.
- High-Quality Diamond Substrates: The successful demonstration of high-finesse âdiamond-likeâ modes validates the use of high-quality, micron-thick diamond membranes, driving demand for advanced CVD diamond growth and fabrication techniques.
View Original Abstract
The nitrogen-vacancy center in diamond has been explored extensively as a light-matter interface for quantum information applications, however it is limited by low coherent photon emission and spectral instability. Here, we present a promising interface based on an alternate defect with superior optical properties (the germanium-vacancy) coupled to a finesse $\approx11{,}000$ fiber cavity, resulting in a $31^{+11}_{-15}$-fold increase in the spectral density of emission. This work sets the stage for cryogenic experiments, where we predict a measurable increase in the spontaneous emission rate.