Zero- and Low-Field Sensing with Nitrogen-Vacancy Centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-04-14 |
| Journal | Physical Review Applied |
| Authors | Philipp J. Vetter, Alastair Marshall, Genko T. Genov, Tim F. Weiss, Nico Striegler |
| Institutions | Hebrew University of Jerusalem, Universidad Politécnica de Cartagena |
| Citations | 29 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Zero- and Low-Field Capability: The research successfully establishes robust magnetic field sensing using Nitrogen Vacancy (NV) centers in diamond without requiring large external bias magnetic fields, overcoming a major limitation of conventional NV protocols.
- Novel Mechanism: This is achieved by exploiting the full S=1 spin nature of the NV center and applying linearly polarized microwave (MW) fields at the Zero-Field Splitting (ZFS) frequency (D â 2.87 GHz), utilizing a hidden effective Raman coupling.
- Enhanced Robustness: New Low-Field Dynamical Decoupling (LDD) sequences (e.g., LDD4a, LDD4b) and optimized GRAPE (Gradient Ascent Pulse Engineering) pulses were developed. These sequences demonstrate superior robustness against frequency detuning (up to 4.2 MHz) and pulse errors compared to standard XY8 protocols.
- High Sensitivity: The method achieved a shot-noise-limited sensitivity of 70 nT/âHz in Ramsey measurements and 8 nT/âHz using optimized Dynamical Decoupling sequences for detecting nearby nuclear spins.
- Broad Applicability: The robust sequences enable precise measurements of weak AC magnetic fields, temperature (utilizing the D parameter shift of â -74 kHz/K), and are crucial for zero-field Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) spectroscopy.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center ZFS (D) | â 2.87 | GHz | Microwave driving frequency |
| 14N Hyperfine Coupling (A) | 2.166 ± 0.006 | MHz | Measured via Ramsey experiment |
| Low-Field Sensitivity (Ramsey) | 70 ± 10 | nT/âHz | Shot-noise-limited estimate |
| DD Sensitivity (9.8 kHz AC) | 8 ± 3 | nT/âHz | Optimized LDD sequence performance |
| Dephasing Time (T2*) | 2.1 ± 0.11 | ”s | Measured via Ramsey experiment |
| Coherence Time (T2(k)) | 500 ± 40 | ”s | Measured using 8-pulse optimized DD sequence |
| Measurement Contrast (Ramsey) | 35.5 ± 0.5 | % | Spin state readout efficiency |
| Rabi Frequency Target (Ω0) | 2Ï * 20 | MHz | Used for Optimal Control (OC) pulse design |
| Pulse Duration (Rectangular) | 25 | ns | Standard pulse length in LDD sequences |
| Detuning Robustness Tested (Î) | Up to 4.219 ± 0.011 | MHz | Range over which LDD sequences maintain high fidelity |
| Temperature Sensitivity (D shift) | â -74 | kHz/K | Used for fluorescence thermometry |
| Magnetic Field Range Tested | 0 to 5 | G | Verification of method applicability |
Key Methodologies
Section titled âKey Methodologiesâ- System Configuration: Experiments were conducted using a room-temperature confocal setup focused on single, micron-deep NV centers in CVD-grown diamond (Element Six, natural 13C abundance).
- Field Generation: Zero- and low-field environments were established using permanent magnets aligned with the NV center symmetry axis.
- Microwave (MW) Excitation: Linearly polarized MW fields were applied via a simple wire spanning the diamond surface. The MW frequency was tuned precisely to the NV center ZFS (D) to induce the hidden effective Raman coupling.
- LDD Sequence Construction: Novel Low-Field Dynamical Decoupling (LDD) sequences (e.g., LDD4a, LDD4b, LDD8a) were analytically derived by restricting MW pulse phases to only 0 or Ï. This restriction reduces the three-level system dynamics to an effective two-level system, allowing for cooperative error compensation.
- Optimal Control (OC) Pulse Design: The GRAPE algorithm was implemented using Julia to numerically optimize pulse pairs. These OC pulses were designed to be robust against detuning (±2.16 MHz), Rabi frequency errors (±10%), and ZFS shifts (±100 kHz).
- Sensing Protocol: Sensing was demonstrated using both Ramsey (Tâ - Ï - Tâ) and Dynamical Decoupling (DD) sequences. The DD sequences (LDD and OC) were used to create narrowband filters for sensing nearby AC magnetic fields (e.g., 300 kHz and 1 MHz).
- Strain Mitigation: Numerical simulations confirmed that LDD sequences show improved performance and robustness even in the presence of local static electric fields (strain) interacting via the linear Stark effect.
Commercial Applications
Section titled âCommercial Applicationsâ- Zero-Field Nano-NMR Spectroscopy: Enables high-resolution structural analysis of molecules by detecting J-coupling (spin-spin coupling) without the interference of large Zeeman interactions caused by bias fields.
- Bio-Sensing and Bio-Imaging: Applicable for non-invasive, nano-scale magnetic field and temperature sensing within living cells, leveraging the NV centerâs bio-compatibility and small size for long-term cell tracking.
- Condensed Matter Research: Allows for the investigation of magnetic dynamics and susceptibility effects in materials that are sensitive to, or perturbed by, external bias magnetic fields.
- High-Precision Thermometry: Provides highly robust fluorescence thermometry, utilizing the temperature-dependent shift of the ZFS parameter (D), suitable for environments with large temperature variations or high strain.
- Quantum Computing and Control: The developed robust pulse sequences (LDD and GRAPE-optimized pulses) are directly transferable to control and decouple noise in other three-level quantum systems, such as trapped ions or atoms.
View Original Abstract
Over the years, an enormous effort has been made to establish nitrogen\nvacancy (NV) centers in diamond as easily accessible and precise magnetic field\nsensors. However, most of their sensing protocols rely on the application of\nbias magnetic fields, preventing their usage in zero- or low-field experiments.\nWe overcome this limitation by exploiting the full spin $S=1$ nature of the NV\ncenter, allowing us to detect nuclear spin signals at zero- and low-field with\na linearly polarized microwave field. As conventional dynamical decoupling\nprotocols fail in this regime, we develop new robust pulse sequences and\noptimized pulse pairs, which allow us to sense temperature and weak AC magnetic\nfields and achieve an efficient decoupling from environmental noise. Our work\nallows for much broader and simpler applications of NV centers as magnetic\nfield sensors in the zero- and low-field regime and can be further extended to\nthree-level systems in ions and atoms.\n