Optically detected magnetic resonance with an open source platform
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-10-09 |
| Journal | SciPost Physics Core |
| Authors | Hossein Babashah, Hoda Shirzad, Elena Losero, V. Goblot, Christophe Galland |
| Institutions | Ăcole Polytechnique FĂ©dĂ©rale de Lausanne |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis paper details the construction and operation of an Optically Detected Magnetic Resonance (ODMR) experimental platform utilizing commercially available hardware and the enhanced open-source Python interface, Qudi.
- Core Platform: Qudi is presented as a modular, open-source Python suite designed for efficient control, data acquisition, and processing in ODMR experiments, lowering the entry barrier for new researchers.
- Hardware Versatility: The setup supports both Continuous Wave (CW) and Pulsed ODMR measurements, accommodating various detectors (analog photodiodes, digital photon counters) and synchronization methods (DAQ cards or oscilloscopes).
- Qudi Enhancements: Key software upgrades include faster data acquisition modes, improved pulse extraction logic for pulsed measurements, compatibility with analog detectors for ensemble studies, and arbitrary/random Microwave (MW) frequency sweeping to mitigate thermal effects.
- Relaxed Requirements: The platform allows NI DAQ cards to function as fast event counters (5 ns resolution), reducing the need for expensive, dedicated time-tagging instruments typically required for single-emitter studies.
- Application Focus: The methodology is validated through detailed characterization of Nitrogen-Vacancy (NV) center ensembles in bulk diamond, providing practical guidelines for optimizing contrast and linewidth.
- Noise Mitigation: Advanced techniques are implemented in Qudi, such as the S0 - S1 difference signal protocol, to suppress spin-independent noise and artifacts arising from laser power fluctuations during pulsed sequences.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Zero Field Splitting (D) | 2.87 | GHz | Ground state triplet |
| NV Center Gyromagnetic Ratio (Îł) | 28 | GHz T-1 | |
| Typical T1 Relaxation Time (Ensemble) | Several | ms | Room temperature, moderate concentration |
| Typical T2* Dephasing Time (Ensemble) | 0.5 - 1 | ”s | Heterogeneous decoherence time |
| Typical T2 Coherence Time (Ensemble) | Few 10s | ”s | Simple Hahn spin-echo sequence |
| Single NV Photon Count Rate | > 100 | kHz | Using Numerical Aperture (NA) > 0.9 and mW laser power |
| Ensemble CW ODMR Contrast | ~2 | % | Optimized contrast for 4 NV orientations |
| DAQ Analog Sampling Resolution (NI-6364) | 0.5 | ”s | Single channel acquisition limit |
| DAQ Digital Time-Tagging Resolution | 5 | ns | NI-6364 card using internal clock (rising/falling edges) |
| MW Source Frequency Switching Speed | ~1 | ms | Minimum per step (e.g., R&S SMF100A) |
| Confocal Spatial Resolution (rmin) | 0.61 * λ / NA | - | Rayleigh criterion limit |
| Confocal Axial Resolution (zmin) | 1.4 * λn / NA2 | - | Depth resolution limit |
Key Methodologies
Section titled âKey MethodologiesâThe ODMR setup integrates optical, microwave, and magnetic field hardware controlled and synchronized via the Qudi software platform.
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Optical Setup and Scanning:
- Microscopy: Utilizes a scanning confocal microscope configuration (Fig. 5), typically epifluorescence, with high-NA objectives (e.g., NA up to 0.9) for diffraction-limited focusing and collection.
- Scanning: Achieved either by moving the sample/objective via piezo stages or by angle-scanning the beam using oscillating mirrors and a 4f relay system.
- Excitation: Off-resonant optical pumping (e.g., green laser for NV centers) is used for spin initialization. Laser power stability is critical to minimize technical noise.
- Pulsing: Optical pulses are generated using Acousto-Optic Modulators (AOMs) or pulsed laser diodes, controlled by a pulse generator.
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Detection and Digitization:
- Detectors: Digital Photon Counters (d-PCs) are used for low-light, single-emitter measurements. Analog Photodetectors (a-PDs) are used for high-flux ensemble measurements.
- Acquisition: Signals are digitized either by a computer-interfaced Data Acquisition (DAQ) card (for analog or digital counting) or directly visualized and stored via a high-speed oscilloscope.
- Qudi Digital Counting: DAQ digital inputs are configured as fast event counters, achieving 5 ns resolution, sufficient for most ODMR dynamics without dedicated time-taggers.
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Microwave (MW) Instrumentation:
- Source: High-stability MW generators (e.g., Rohde & Schwarz) are preferred for metrology, capable of frequency sweeping (CW) or external pulse modulation (pulsed).
- Delivery: MW radiation is delivered to the sample via specialized antennas (e.g., wire loops, split-ring resonators) designed for spatial homogeneity over the ensemble area.
- Pulsing: MW pulses are carved out of the CW source using fast external switches, synchronized by the pulse generator.
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Synchronization and Averaging (Pulsed ODMR):
- Pulse Sequences: Qudi controls the pulse generator to implement standard sequences (Rabi, Ramsey, Hahn Echo) by synchronizing laser and MW pulses.
- Averaging Strategies: Two main methods are supported: âNPâ (individual sequence repetition N times) and âPNâ (full series of P sequences repeated N times).
- Noise Rejection: For T1 measurements, the S0 - S1 difference protocol is used, involving a Ï-pulse inversion before readout to remove spin-independent noise (e.g., laser ionization effects).
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Bias Magnetic Field:
- Implementation: DC magnetic fields are generated using permanent magnets on micro-stages or, for higher precision and control, three-axis Helmholtz coils.
- Purpose: Tailors the system eigenstates, allowing for specific level anti-crossing configurations (GSLAC/ESLAC) or optimizing sensitivity for magnetometry applications.
Commercial Applications
Section titled âCommercial ApplicationsâThe ODMR platform and the enhanced Qudi interface are critical enablers for several high-tech and material science sectors:
- Quantum Sensing and Metrology:
- Nanoscale detection and imaging of magnetic fields, electric fields, temperature, and strain using NV centers.
- Development of highly sensitive magnetometers for biomedical applications (biosensing, tracking magnetic nanoparticles).
- Quantum Information Processing:
- Characterization and manipulation of solid-state spin qubits (NV centers, SiV, rare earth ions).
- Development of long-lasting quantum memories (rare earth ions in crystal lattices).
- Material Science and Characterization:
- Spectroscopy and characterization of novel ODMR-active materials, including color centers in diamond, silicon carbide (SiC), and hexagonal boron nitride (hBN).
- Study of spin dynamics and coherence properties (T1, T2) in various solid-state environments.
- RF and Microwave Technology:
- Wide-bandwidth instantaneous radio frequency spectrum analysis.
- Development and testing of room-temperature solid-state masers and spin refrigerators.
- Biomedical and Life Sciences:
- Use of NV-doped nanodiamonds as biocompatible biomarkers for cell tracking and diagnostics.
- Quantum relaxometry for sensing free radical production and metabolic activity in living cells.
View Original Abstract
Localized electronic spins in solid-state environments form versatile and robust platforms for quantum sensing, metrology and quantum information processing. With optically detected magnetic resonance (ODMR), it is possible to prepare and readout highly coherent spin systems, up to room temperature, with orders of magnitude enhanced sensitivities and spatial resolutions compared to induction-based techniques, allowing for single spin manipulations. While ODMR was first observed in organic molecules, many other systems have since then been identified. Among them is the nitrogen-vacancy (NV) center in diamond, which is used both as a nanoscale quantum sensor for external fields and as a spin qubit. Other systems permitting ODMR are rare earth ions used as quantum memories and many other color centers trapped in bulk or 2-dimensional host materials. In order to allow the broadest possible community of researchers and engineers to investigate and develop novel ODMR-based materials and applications, we review here the setting up of ODMR experiments using commercially available hardware. We also present in detail the dedicated collaborative open-source interface named Qudi and describe the features we added to speed-up data acquisition, relax instrument requirements and extend its applicability to ensemble measurements. Covering both hardware and software development, this article aims to overview the setting of ODMR experiments and provide an efficient, portable and collaborative interface to implement innovative experiments to optimize the development time of ODMR experiments for scientists of any backgrounds.