High-sensitivity nanoscale quantum sensors based on a diamond micro-resonator
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-18 |
| Journal | Communications Materials |
| Authors | Ryota Katsumi, Kosuke Takada, K. Kawai, Daichi Sato, Takashi Yatsui |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Breakthrough: Demonstration of high-sensitivity, nanoscale quantum sensing using on-chip diamond micro-ring resonators integrated onto a cutting-edge photonic chip platform.
- High Sensitivity Achieved: The device experimentally achieved a magnetic sensitivity of 1.0 ”T/âHz without relying on complex pulse sequences, representing a significant milestone for practical quantum sensors.
- Projected Performance: Numerical simulations predict a sensitivity improvement up to 1.3 nT/âHz by leveraging efficient photon extraction via SiN photonic waveguide coupling.
- High Contrast ODMR: The micro-ring resonator, containing an ensemble of NV centers (density 5.3 x 1016 cm-3), achieved an electron-spin resonance contrast of 25%, close to the theoretical limit (30%).
- Coherence Time: The fabricated nanostructure maintained a long spin coherence time (T2 = 6.0 ”s), which is advantageous for the new sensing regime.
- Integration Method: Hybrid integration was achieved using a deterministic âpick-flip-and-place transfer printingâ technique, enabling the creation of high-Q nanocavities on standard CMOS-compatible platforms (SiN/SiO2).
- Efficiency: The ring resonator confines photons in a nanoscale region, enabling efficient use of emitted photons and significantly reducing data acquisition times compared to standard probe approaches.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Experimental AC Sensitivity | 1.0 | ”T/âHz | Achieved without pulse techniques |
| Projected AC Sensitivity | 1.3 | nT/âHz | With SiN waveguide coupling |
| NV Center Density | 5.3 x 1016 | cm-3 | Diamond substrate specification |
| Ring Resonator Radius | 1.3 (2.3) | ”m | Typical fabricated dimensions |
| Ring Resonator Width | 440 (650/800) | nm | Typical fabricated dimensions |
| Experimental Q-Factor (TE Mode) | 1000 (2200) | Dimensionless | Ring radius 1.3 ”m (2.3 ”m) |
| Experimental Q-Factor (TM Mode) | 1300 (2300) | Dimensionless | Ring radius 1.3 ”m (2.3 ”m) |
| Simulated Q-Factor (TE Mode) | 42,000 | Dimensionless | FDTD simulation, λres ~700 nm |
| ODMR Contrast (Experimental) | 25 | % | Measured on-chip, near theoretical limit |
| Spin Coherence Time (T2) | 6.0 | ”s | Measured via Hahn echo |
| Spin Dephasing Time (T2*) | 700 | ns | Measured via Ramsey interferometry |
| Microwave Ï-Pulse Duration | 230 | ns | Used for Rabi oscillation |
| Emitter-to-Waveguide Coupling (ηNV) | 89 | % | Simulated, using SiN waveguide |
| Cavity Mode Volume | 0.32 | ”m3 | Small mode volume |
| Excitation Wavelength | 532 | nm | Stable continuous-wave laser |
| Lock-in AC Field Frequency | 1 | kHz | Used for sensitivity evaluation |
| Photon Count Rate (Estimated Icount) | 21 | Mcps | For 10 mW saturation excitation power |
Key Methodologies
Section titled âKey MethodologiesâThe device fabrication and characterization relied on advanced nanofabrication and quantum control techniques:
-
SiN Hard Mask Fabrication:
- A 200-nm-thick SiN layer on a SiO2/Si substrate (1 ”m SiO2) was used.
- Cavity patterns were defined using electron beam lithography (EBL) on ZEP520A resist.
- CF4-based dry etching followed by O2 plasma ashing removed residual resist.
- Air-suspension was achieved via chemical wet etching using buffered hydrofluoric acid (BHF), followed by critical point drying.
-
Diamond Ring Resonator Etching:
- Patterns were transferred from the SiN mask to the diamond substrate (DNV-B1, Element Six).
- Oxygen/Argon (O2/Ar) plasma RIE was used for vertical dry etching.
- Angled plasma etching was performed inside a conical Faraday cage to undercut the structures and form the ring resonators connected to the substrate.
- Residual SiN masks were removed using BHF.
-
Hybrid Integration (Pick-Flip-and-Place Transfer Printing):
- The diamond ring structure was lifted using a PDMS film with weak adhesion (Gel-Pack PF-40 x 40-0065-X0).
- The film was flipped, and the structure was transferred to a PDMS film with stronger adhesion (Gel-Pack PF-40 x 40-0065-X8).
- The ring structure was placed onto the low-refractive index SiO2 substrate by slowly peeling off the adhesive film, ensuring a flat interface.
-
Spin Manipulation and Measurement:
- A microwave antenna (120 ”m) was implemented on the photonic chip for uniform microwave excitation.
- Pulsed green laser (532 nm) was generated using an acousto-optic modulator (AOM) and pulse generator.
- Spin states were manipulated using a fast microwave switch for generating Ï/2 and Ï pulses (Rabi, Ramsey, Hahn echo sequences).
- Sensitivity was evaluated by applying a 1 kHz AC magnetic field via a circular coil and detecting the resulting PL fluctuation using a lock-in amplifier (Stanford Research Systems SR830) and an APD.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of chip-scale, high-sensitivity NV diamond sensors is critical for miniaturizing quantum devices across several high-value sectors:
-
Biomedical and Medical Diagnostics:
- Detection of weak magnetic fields from the brain and heart (e.g., magnetocardiography).
- Nanoscale detection of chemical and biomedical information (e.g., single-molecule magnetic resonance spectroscopy).
- Optical magnetic imaging of living cells and single-neuron action potentials.
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Condensed Matter Physics and Materials Science:
- Probing fundamental spin dynamics and quantum magnetic phenomena in 2D materials (requires sub-nanometer distance sensing).
- High-resolution magnetic resonance spectroscopy (NMR/MRI) at the nanoscale.
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Integrated Photonics and Quantum Computing:
- Development of compact, functionalized quantum-sensing devices compatible with CMOS technology.
- Realization of nano-lasers using ensemble NV centers as the gain material, potentially enabling femtotesla-scale sensitivity.
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Geological and Environmental Sensing:
- Micrometer-scale magnetic imaging of geological samples.
- Detection of various nanoscale physical quantities in chemistry and environmental monitoring.
View Original Abstract
Abstract Nitrogen-vacancy centers have demonstrated significant potential as quantum magnetometers for nanoscale phenomena and sensitive field detection, attributed to their exceptional spin coherence at room temperature. However, it is challenging to achieve solid-state magnetometers that can simultaneously possess high spatial resolution and high field sensitivity. Here we demonstrate nanoscale quantum sensing with high field sensitivity by using on-chip diamond micro-ring resonators. The ring resonator enables the efficient use of photons by confining them in a nanoscale region, enabling the magnetic sensitivity of 1.0 ÎŒT/ $$\sqrt{{\mbox{Hz}}}$$ Hz on a photonic chip with a measurement contrast of theoretical limit. We also show that the proposed on-chip approach can improve the sensitivity via efficient light extraction with photonic waveguide coupling. Our work provides a pathway toward the development of chip-scale packaged sensing devices that can detect various nanoscale physical quantities for fundamental science, chemistry, and medical applications.