All-optical nuclear quantum sensing using nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-10 |
| Journal | npj Quantum Information |
| Authors | Beat BĂŒrgler, Tobias F. Sjolander, Ovidiu Brinza, Alexandre Tallaire, Jocelyn Achard |
| Institutions | Centre National de la Recherche Scientifique, Sorbonne Université |
| Citations | 22 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel, purely optical method for coherent quantum sensing using the 15N nuclear spin of the Nitrogen-Vacancy (NV) center in diamond, eliminating the need for traditional microwave (MW) or radio-frequency (RF) driving.
- Core Innovation: Demonstration of all-optical Free Induction Decay (FID) measurementsâthe key protocol for low-frequency quantum sensingâon both single NV centers and NV ensembles.
- Microwave-Free Operation: The scheme overcomes major limitations of conventional NV sensing (miniaturization, energy efficiency, and non-invasiveness) by relying solely on optical driving and static magnetic fields.
- Coherent Initialization: Coherent superposition states of the 15N nuclear spin are prepared by optically pumping the NV center near the Excited State Level Anti-Crossing (ESLAC) in the presence of a small, static transverse magnetic field (Bperp).
- Performance Metrics: Achieved nuclear spin coherence times (T2*) up to 508.5 ”s in NV ensembles, significantly longer than typical electron spin coherence times.
- Optimal Conditions: Maximum FID contrast (Cmax ~4.2%) was observed at an optimal transverse magnetic field of approximately 8.6 G, corresponding to a tilt angle (Ίopt) of ~0.86°.
- Projected Sensitivity: The all-optical protocol projects competitive shot-noise-limited sensitivities for ensemble magnetometry (1.22 nT Hz-1/2) and gyroscopy (135° hour-1/2).
- Theoretical Framework: The dynamics are accurately modeled using an effective Hamiltonian derived via Van Vleck perturbation theory, confirming the role of the transverse field in tilting the nuclear quantization axis.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensing Resource | 15N Nuclear Spin (I=1/2) | - | Nitrogen-Vacancy (NV) Center |
| Electron Spin | S=1 | - | Quantized along NV axis |
| Electron Gyromagnetic Ratio (Îłs) | 2.8 | MHz G-1 | - |
| Nuclear Gyromagnetic Ratio (ÎłI) | 431.7 | Hz G-1 | - |
| Ground State ZFS (Dgs) | 2.87 | GHz | Zero-Field Splitting |
| Optimal Transverse Field (Bperp) | ~8.6 | G | Maximizes FID contrast |
| Optimal Tilt Angle (Ίopt) | ~0.86 | ° | - |
| Max FID Contrast (Cmax) | ~4.2 | % | Measured at Bext = 533 G |
| Single NV Coherence Time (T2*) | 248.1 ± 12.4 | ”s | All-optical FID measurement |
| Ensemble NV Coherence Time (T2*) | 508.5 ± 17.4 | ”s | All-optical FID measurement |
| Projected Ensemble Magnetometry Sensitivity | 1.22 | nT Hz-1/2 | Shot noise limited |
| Projected Ensemble Gyroscopy Sensitivity | 135 | ° hour-1/2 | Shot noise limited |
| Excitation Wavelength | 515 | nm | Green laser (Cobolt 06-MLD) |
| Single NV Laser Power | ~50 | ”W | Used for single nanopillar NV |
| Ensemble NV Laser Power | 2.2 | mW | Used for bulk unstructured diamond |
| Single NV Implantation Depth | ~9 | nm | Nominal depth (6 keV 15N ions) |
| Ensemble NV Density | ~300 | ppb | Estimated 15NV density |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Preparation (Single NV): Electronic grade diamond was implanted with singly charged 15N ions (6 keV, flux 1011 cm-2). Subsequent fabrication of parabolic diamond pillars enhanced photoluminescence (PL) collection efficiency.
- Sample Preparation (Ensemble NV): Unstructured diamond was grown via Chemical Vapor Deposition (CVD) along the (113) crystal orientation to promote preferential NV alignment. The growth used 12C and 15N enriched gas mixture, resulting in an estimated NV density of ~300 ppb.
- Optical Setup: Experiments were conducted using a home-built confocal microscope (NA = 0.8) employing a 515 nm green laser for excitation and collecting red PL for readout.
- Magnetic Field Control: A static magnetic field (Bext) was generated by a permanent neodymium disk magnet. This magnet was mounted on linear and goniometric stages for precise tuning of the field strength and tilt angle (Ί) near the NV Excited State Level Anti-Crossing (ESLAC).
- All-Optical FID Protocol: The measurement sequence consists of a green laser pulse separated by a variable free evolution delay (Ï). The initial 350 ns of the pulse performs optical nuclear spin readout, while the remainder of the pulse (total duration 3 ”s) reinitializes the spin system.
- Theoretical Modeling: The system dynamics were simulated using a numerical model combining classical rate equations (for optical pumping) and master equations (for quantum evolution). An effective Hamiltonian for the 15N spin was derived using Van Vleck perturbation theory to predict precession frequency and quantization axis.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of all-optical, MW/RF-free coherent quantum sensing opens pathways for highly integrated and power-efficient devices in several key sectors:
- Integrated Quantum Sensors: Enables the fabrication of highly compact, chip-scale quantum sensors by removing bulky and power-hungry MW/RF components.
- Inertial Navigation and Gyroscopy: Provides a foundation for next-generation solid-state gyroscopes with competitive projected sensitivities (135° hour-1/2), suitable for autonomous systems and high-precision navigation.
- Non-Invasive Magnetometry: Ideal for remote sensing applications (e.g., via optical fibers) or in environments where MW/RF fields must be avoided, such as sensitive biological or material science samples.
- Medical and Biological Imaging: Potential for high-sensitivity magnetic detection of biological processes (e.g., single-neuron action potentials) without introducing RF heating or interference.
- Fundamental Physics Research: Applicable to studying analogous dynamics in other novel solid-state color centers that exhibit suitable level anti-crossing behavior and coupling to nuclear spins.
View Original Abstract
Abstract Solid state spins have demonstrated significant potential in quantum sensing with applications including fundamental science, medical diagnostics and navigation. The quantum sensing schemes showing best performance under ambient conditions all utilize microwave or radio-frequency driving, which poses a significant limitation for miniaturization, energy efficiency, and non-invasiveness of quantum sensors. We overcome this limitation by demonstrating a purely optical approach to coherent quantum sensing. Our scheme involves the 15 N nuclear spin of the Nitrogen-Vacancy (NV) center in diamond as a sensing resource, and exploits NV spin dynamics in oblique magnetic fields near the NVâs excited state level anti-crossing to optically pump the nuclear spin into a quantum superposition state. We demonstrate all-optical free-induction decay measurementsâthe key protocol for low-frequency quantum sensingâboth on single spins and spin ensembles. Our results pave the way for highly compact quantum sensors to be employed for magnetometry or gyroscopy applications in challenging environments.