Demonstration of NV-detected ESR spectroscopy at 115 GHz and 4.2 T
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-04-27 |
| Journal | Applied Physics Letters |
| Authors | Benjamin Fortman, Junior Peña, Karoly Holczer, Susumu Takahashi, Benjamin Fortman |
| Institutions | University of Southern California |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates the successful implementation of Nitrogen-Vacancy (NV)-detected Electron Spin Resonance (ESR) spectroscopy at high magnetic fields, providing a critical advancement for nanoscale quantum sensing.
- High-Field Demonstration: NV-ESR was successfully performed at a Larmor frequency of 115 GHz, corresponding to a high magnetic field of 4.2 Tesla. This high field significantly improves spectral resolution and separation compared to conventional low-field NV-ESR.
- Target Spin Detection: The technique utilized the Double Electron-Electron Resonance (DEER) sequence to detect and characterize single-substitutional nitrogen impurities (P1 centers) in diamond, confirming excellent agreement with simulated P1 spectra.
- Coherent Control Enhancement: Linear frequency-swept chirp pulses were introduced to the NV center control sequence. This technique achieved nearly 100% population inversion, drastically improving fidelity and excitation bandwidth compared to standard rectangular pulses (~40% inversion).
- Improved Coherence Time: The use of chirp pulses in the single NV experiment resulted in a spin decoherence time (T2) of approximately 20 µs, a substantial improvement over the 2.4 ± 0.3 µs observed in the ensemble system using rectangular pulses.
- Foundation for HF NV-NMR: This work establishes the necessary basis for high-frequency NV-detected Nuclear Magnetic Resonance (HF NV-NMR) spectroscopy, enabling high-resolution studies of external spins in complex, heterogeneous environments.
- Future Scalability: The presented system is designed for potential extension to an ESR Larmor frequency of 230 GHz (corresponding to 8.2 Tesla) for even greater spectral resolution.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Larmor Frequency | 115 | GHz | Operating frequency for NV-ESR. |
| Magnetic Field (B0) | 4.2 | Tesla | Corresponding field for 115 GHz operation. |
| Magnet System Capacity | 12.1 | Tesla | Cryogenic-free superconducting magnet maximum field. |
| HF MW Output Power | 480 | mW | Output power used at 115 GHz. |
| MW Source Frequency Range | 107-120 / 215-240 | GHz | Dual-band capability for DEER and future extension. |
| Ensemble T2 (Rectangular Pulse) | 2.4 ± 0.3 | µs | Measured spin echo relaxation time. |
| Single NV T2 (Chirp Pulse) | ~20 | µs | Measured spin echo relaxation time. |
| Rectangular Pulse Inversion | ~40 | % | Estimated population inversion efficiency. |
| Chirp Pulse Inversion | Nearly 100 | % | Achieved population inversion efficiency. |
| P1 Center Linewidth | ~2 | MHz | Observed linewidth in high-resolution NV-ESR spectrum. |
| Sample Type | (111)-cut Type-Ib | Diamond | High-pressure, high-temperature synthesis. |
| Sample Size | 2.0 x 2.0 x 0.3 | mm3 | Dimensions of the diamond crystals used. |
| Electron Irradiation Energy | 4 | MeV | Used for ensemble sample preparation. |
| Electron Fluence | 1.2 x 1018 | e-/cm2 | Total exposure to increase NV density. |
| Annealing Temperature | 1000 | °C | Post-irradiation annealing process. |
Key Methodologies
Section titled “Key Methodologies”The experiment utilized a custom-built High-Frequency Optically Detected Magnetic Resonance (HF ODMR) system integrated with a high-field magnet and advanced microwave pulsing capabilities.
- System Setup: The HF ODMR system combined a 12.1 Tesla cryogenic-free superconducting magnet, a confocal microscope for optical initialization/readout, and a HF microwave source (Virginia Diodes, Inc.). Quasioptics and a corrugated waveguide were used for low-loss, broadband microwave propagation to the sample stage.
- Sample Preparation: The ensemble diamond sample was subjected to 4 MeV electron beam irradiation (1.2 x 1018 e-/cm2 fluence) followed by annealing at 1000 °C to achieve an NV/N ratio of approximately 8%.
- NV Characterization: Pulsed ODMR and Rabi oscillation measurements were performed to determine the NV center alignment (1.6° polar angle from the [111] axis) and to calibrate the π/2 and π pulse lengths (e.g., 212 ns and 402 ns, respectively, for ensemble).
- Ensemble NV-ESR: The Double Electron-Electron Resonance (DEER) sequence was implemented. This sequence involves an NV spin echo (MW1 pulses) combined with a separate MW pulse (MW2) applied at the target spin frequency (P1 centers). Successful P1 detection was confirmed by observing five distinct reductions in NV fluorescence intensity.
- Single NV Coherent Control: For the single NV experiment, chirp pulses (linear frequency-swept pulses) were generated using an IQ mixer controlled by an arbitrary waveform generator (AWG).
- Chirp Pulse Optimization: Chirp pulses were applied to the NV center to leverage adiabatic passage, maximizing population transfer efficiency to nearly 100% and significantly extending the measured T2 time to ~20 µs.
- Single NV-ESR: The DEER sequence was repeated using the optimized chirp pulses for the NV control (MW1), demonstrating clear, high-resolution detection of the three resolved peaks corresponding to the P1 center hyperfine splitting.
Commercial Applications
Section titled “Commercial Applications”The demonstration of high-field, high-resolution NV-ESR spectroscopy is critical for advancing quantum technologies and nanoscale characterization across several high-value sectors.
- Quantum Computing and Information:
- High-fidelity spin control (using chirp pulses) is essential for robust quantum gate operations and minimizing errors in diamond-based quantum processors.
- Enables precise characterization of spin defects (like P1 centers) that act as noise sources or potential qubits in diamond quantum architectures.
- Nanoscale Sensing and Metrology:
- Development of ultra-sensitive magnetic field sensors capable of operating in high-field environments (up to 8.2 Tesla), necessary for advanced laboratory equipment.
- Detection of external spins (e.g., surface spins, radical species) with high spectral separation, eliminating interference from unwanted g=2 signals common at low fields.
- Biophysics and Structural Biology:
- HF NV-NMR Spectroscopy: Provides the basis for high-resolution NMR of small numbers of molecules, allowing structural and dynamic investigations of biomacromolecules (proteins, enzymes) in complex, heterogeneous environments (e.g., within cells or on solid surfaces).
- High Larmor frequency minimizes sensitivity to motional narrowing, allowing ESR investigation of structures for molecules in motion.
- Materials Characterization:
- Investigation of chemical environments and spin dynamics at solid-state surfaces and interfaces, crucial for optimizing catalysts, batteries, and semiconductor materials.
- Detection of nanoscale heterogeneity in spin systems within complex materials.
View Original Abstract
High frequency electron spin resonance (ESR) spectroscopy is an invaluable tool for identification and characterization of spin systems. Nanoscale ESR using the nitrogen-vacancy (NV) center has been demonstrated down to the level of a single spin. However, NV-detected ESR has exclusively been studied at low magnetic fields, where the spectral overlap prevents clear identification of spectral features. In this work, we demonstrate NV-detected ESR measurements of single-substitutional nitrogen impurities in diamond at a NV Larmor frequency of 115 GHz and the corresponding magnetic field of 4.2 T. The NV-ESR measurements utilize a double electron-electron resonance sequence and are performed using both ensemble and single NV spin systems. In the single NV experiment, chirp pulses are used to improve the population transfer and for NV-ESR measurements. This work provides the basis for NV-based ESR measurements of external spins at high magnetic fields.