| Metadata | Details |
|---|
| Publication Date | 2023-10-17 |
| Journal | Communications Physics |
| Authors | Jonas Meinel, Minsik Kwon, R. Maier, Durga Bhaktavatsala Rao Dasari, Hitoshi Sumiya |
| Institutions | Max Planck Institute for Solid State Research, University of Stuttgart |
| Citations | 9 |
| Analysis | Full AI Review Included |
- Core Innovation: Introduction of an Electron Nuclear Double Resonance Quantum Heterodyne (ENDOR Qdyne) protocol enabling high-resolution nanoscale Nuclear Magnetic Resonance (NMR) spectroscopy applicable at arbitrary (including high) magnetic fields.
- High-Field Capability: The method eliminates the need for microwave (MW) Ï-pulses faster than the nuclear Larmor frequency (a requirement for conventional Qdyne), allowing extension to high fields (e.g., 8 T) where chemical shift resolution is maximized.
- Spectral Resolution: Demonstrated a spectral resolution (decay rate Î) of 0.6 ± 0.1 kHz on a single weakly coupled 13C nuclear spin (Azz = 6 kHz).
- Performance Comparison: The ENDOR Qdyne decay rate (0.6 kHz) was significantly better than the conventional Dynamical Decoupling (DD)-based Qdyne protocol (1.4 ± 0.3 kHz) measured on the same spin.
- Decoherence Mechanism Identified: The primary linewidth-limiting decoherence source was identified as the combination of NV-spin-initialization infidelity ($f \approx 0.9$) and strong sensor-target coupling (Azz).
- Future Resolution Potential: Theoretical prediction suggests achieving a 1 Hz linewidth for 1H target spins at an NV depth of 4.2 nm.
- Mechanism: Transverse nuclear spin polarization (Ix, Iy) is converted to longitudinal polarization (Iz) using phase-coherent Radio Frequency (RF) pulses, which is then sensed via the static hyperfine interaction (SzIz) using a Ramsey sequence.
| Parameter | Value | Unit | Context |
|---|
| Magnetic Field (B) | 0.25 | T | Proof-of-principle experiment (moderate field) |
| Target Nucleus | Single 13C | Spin-1/2 | Weakly coupled to NV center |
| Hyperfine Coupling (Azz) | 6 | kHz | For the demonstrated 13C spin |
| 13C Larmor Frequency | 2.336 ± 0.018 | kHz | Measured via ENDOR Qdyne |
| ENDOR Qdyne Decay Rate (Î) | 0.6 ± 0.1 | kHz | Measured on 13C (Azz = 6 kHz) |
| Conventional Qdyne Decay Rate (Î) | 1.4 ± 0.3 | kHz | Measured on same 13C spin |
| Lowest Observed Linewidth | 27 ± 9 | Hz | Observed for NV-13C pairs with Azz < 70 Hz |
| Required MW Pulse Length (Conventional) | < 8 | ns | Required for 120 MHz proton Larmor (3 T field) |
| NV Electron T2* Lifetime | 50 | ”s | Typical lifetime in the 12C-enriched diamond |
| NV Electron T2 Lifetime | â 300 | ”s | Typical lifetime in the 12C-enriched diamond |
| NV Initialization Fidelity ($f$) | â 0.9 | Dimensionless | Used in decoherence modeling |
| Diamond Enrichment | 99.995 | % | 12C enrichment |
| Electron Irradiation Fluence | 1.3 x 1011 | cm-2 | Used for NV creation (2 MeV electrons) |
| Annealing Temperature | 1000 | °C | Post-irradiation annealing (2 h in vacuum) |
| Predicted 1H Linewidth (Goal) | 1 | Hz | Predicted at NV depth (dNV) of 4.2 nm |
The experiment utilizes a confocal room-temperature single NV setup combined with arbitrary waveform generators for precise spin control.
- Material: (111)-oriented polished diamond slice (2 mm x 2 mm x 80 ”m).
- Growth: High-pressure high-temperature (HPHT) method (5.5 GPa, 1350 °C) using high-purity Fe-Co-Ti solvent and 12C-enriched solid carbon.
- NV Generation: Intrinsic nitrogen was used. Irradiation performed with 2 MeV electrons at room temperature, total fluence 1.3 x 1011 cm-2.
- Post-Processing: Annealed at 1000 °C for 2 hours in vacuum.
The protocol combines ENDOR methods with quantum heterodyne measurements to sample nuclear precession phase coherently across multiple electron spin detection runs.
| Step | Action | Purpose / Mechanism |
|---|
| Initialization | Optical excitation (520 nm laser) | Initializes NV electron spin into ms = 0 state. |
| Nuclear Polarization | Pulse-pol sequence | Hyperpolarizes the target 13C nuclear spin. |
| Precession Start | (Ï/2)ref RF pulse | Prepares the nuclear spin in the superposition state (e.g., |+y>). |
| Free Evolution (Tfid) | Nuclear spin precesses freely | Acquires phase (ÎÏTfid) relative to the coherent RF source. |
| Phase Mapping (Ix â Iz) | (3Ï/2)ref+Ί RF pulse | Rotates the nuclear spin polarization from the transverse plane (Ix, Iy) to the measurement basis (Iz). |
| Sensing Block (Tsens) | Ramsey sequence on NV spin | Maps the nuclear Iz polarization onto the NV electron spin (Sz) via the static hyperfine interaction (AzzSzIz). |
| Readout | Laser pulse | Optically reads out the NV electron spin state (Sz). |
| Back Rotation (Iz â Ix) | (Ï/2)ref+Ί RF pulse | Rotates the nuclear spin back into the transverse plane to continue free evolution. |
| Repetition | Protocol repeated M times | Samples the nuclear oscillation phase coherently. |
| Industry / Field | Application | Relevance to ENDOR Qdyne |
|---|
| Nanoscale NMR Spectroscopy | High-resolution chemical analysis of ultra-small samples (micro- to nanoscales). | Enables chemical shift and J-coupling resolution by operating at high magnetic fields (e.g., 8 T). |
| Quantum Sensing | Development of robust, high-fidelity quantum sensors based on NV centers. | Overcomes the fundamental T1 limit of the sensor spin, enhancing spectral resolution beyond conventional limits. |
| Structural Biology / Chemistry | NMR study of proteins, short-lived molecules, and molecular dynamics in confined volumes. | High-field capability increases thermal polarization and sensitivity, reducing the required sensing volume. |
| Solid-State Physics | Characterization of nuclear spin baths and hyperfine dynamics in diamond and other host materials. | Provides a method to study decoherence mechanisms (like initialization infidelity) in detail across varying coupling strengths (Azz). |
| Advanced Materials Characterization | Surface NMR experiments on diamond or other materials where target nuclei are weakly coupled and distant from the sensor. | ENDOR Qdyne is advantageous for sensing distant ensembles of weakly coupled nuclear spins, crucial for surface NMR. |
View Original Abstract
Abstract Nitrogen vacancy (NV) centers are a major platform for the detection of nuclear magnetic resonance (NMR) signals at the nanoscale. To overcome the intrinsic electron spin lifetime limit in spectral resolution, a heterodyne detection approach is widely used. However, application of this technique at high magnetic fields is yet an unsolved problem. Here, we introduce a heterodyne detection method utilizing a series of phase coherent electron nuclear double resonance sensing blocks, thus eliminating the numerous Rabi microwave pulses required in the detection. Our detection protocol can be extended to high magnetic fields, allowing chemical shift resolution in NMR experiments. We demonstrate this principle on a weakly coupled 13 C nuclear spin in the bath surrounding single NV centers, and compare the results to existing heterodyne protocols. Additionally, we identify the combination of NV-spin-initialization infidelity and strong sensor-target-coupling as linewidth-limiting decoherence source, paving the way towards high-field heterodyne NMR protocols with chemical resolution.