Time-space-encoded readout for noise suppression and scalable scanning in optically active solid-state spin systems
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-06 |
| Journal | Physical Review Applied |
| Authors | Joachim P. Leibold, Nick R. von Grafenstein, Xiaoxun Chen, Linda MĂŒller, Karl D. Briegel |
| Institutions | Munich Center for Quantum Science and Technology, Technical University of Munich |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research introduces the Time-to-Space (T2S) encoding readout scheme, a major advancement for optically active solid-state spin systems, designed for engineers focused on quantum sensing scalability and noise mitigation.
- Core Innovation: T2S decouples uniform Microwave (MW) spin manipulation from rapid, spatially scanned optical readout, achieved using fast Acousto-Optic Modulators (AOMs) driven by multi-frequency RF pulse trains.
- Noise Rejection: The scheme enables correlated measurements, achieving efficient common-mode noise cancellation (e.g., 60% reduction in MW phase noise) by simultaneously controlling reference and sample spin ensembles.
- Performance Gain: Demonstrated a 3x improvement in Signal-to-Noise Ratio (SNR) for 1H NMR sensing, equivalent to nearly an order of magnitude reduction in required measurement time.
- Scalability: T2S facilitates scalable multipixel imaging without requiring complex, high-speed cameras, relying instead on fast AOM scanning capabilities.
- Acceleration Potential: The method projects massive data acquisition acceleration, potentially yielding up to 400 readouts per MW pulse sequence in T1-limited experiments (1 ms duration).
- Implementation Ease: The T2S scheme is straightforward to implement, utilizing only components already standard in pulsed Optically Detected Magnetic Resonance (ODMR) setups.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Shallow NV Depth | ~5 | nm | Used for T1 and XY8 measurements. |
| Thick NV Layer Thickness | ~10 | ”m | Used for high-sensitivity CASR NMR experiments. |
| T1 Relaxation Time (Reference) | 1.1 ± 0.05 | ms | Plain diamond spot (room temperature ensemble). |
| T1 Relaxation Time (Mn2+ Coated) | 0.5 ± 0.03 | ms | Reduced T1 due to paramagnetic surface ions. |
| T2 Coherence Time (Limit) | 100 | ”s | Used for calculating maximum readouts (40 spots). |
| Minimum Readout Time per Spot | 2.5 | ”s | Includes 2 ”s laser pulse + 0.5 ”s spot movement. |
| AOM Drive Frequency Bandwidth | 80 | MHz | Typical bandwidth for quartz crystal AOM. |
| AOM Acoustic Velocity (Quartz) | 5.7 | mm/”s | Acoustic velocity in the crystal. |
| Theoretical Resolvable Spots (1D) | 31 | - | Limited by AOM bandwidth and spot size. |
| Projected 2D Scanning Resolution | 50 x 50 | spots | Achievable using two orthogonal AODs (Appendix G). |
| SNR Improvement (1H NMR) | 3x | - | Achieved via time-domain subtraction. |
| Noise Reduction (MW Phase Noise) | 60 | % | Achieved by common-mode subtraction. |
| 1H NMR Water Peak Frequency | ~5000 | Hz | Measured using CASR sequence. |
| MW Frequency (0 â +1 transition) | ~5.22 | GHz | Used for N-V spin control. |
Key Methodologies
Section titled âKey MethodologiesâThe T2S scheme modifies standard pulsed ODMR setups by leveraging the fast scanning capabilities of Acousto-Optic Modulators (AOMs).
- Homogeneous Spin Control: MW pulse sequences (e.g., T1, XY8-N, CASR) were applied simultaneously and uniformly across the entire region of interest using a loop antenna, ensuring parallel manipulation of all spin ensembles.
- AOM RF Modification: The standard single-tone RF input to the AOM driver was replaced with a rapid train of pulses, each pulse driven by a distinct RF frequency (f1, f2, f3, etc.).
- Time-to-Space Encoding: Each unique RF frequency corresponds to a specific deflection angle (Ξ) and thus a specific laser spot position (D = Ξscan * F) on the diamond surface. The time of the readout pulse is directly linked to the spatial position.
- Fast Readout Cycle: The AOMâs fast response time (nanosecond scale) allows the laser spot to be moved and fluorescence read out in approximately 2.5 ”s per spot (2 ”s laser pulse + 0.5 ”s movement time). This speed is critical to complete multiple readouts before the spin state decays (T1 relaxation time, typically milliseconds).
- Correlated Measurement Setup: For noise rejection, two spots were defined: one beneath the sample (e.g., water in a microfluidic channel) and one beneath a reference (e.g., glass). Since the MW sequence acts globally, common noise is encoded identically in both spots.
- Noise Cancellation: Data acquisition (DAQ) recorded the fluorescence intensity for both spots sequentially in time. Common-mode noise was rejected by subtracting the time-domain data sets before performing the Fourier transform (for NMR analysis).
- Scalability Implementation: For multi-spot imaging, an Arbitrary Waveform Generator (AWG) was used to synthesize the complex RF pulse train, offering maximum flexibility in frequency, duration, and pulse shape for defining a larger number of spots.
Commercial Applications
Section titled âCommercial ApplicationsâThe T2S encoding scheme offers significant advantages for industries requiring high-sensitivity, high-throughput quantum sensing and microscopy.
- Quantum Sensing and Metrology:
- High-Precision Magnetometry: Enabling highly sensitive ensemble NV-diamond magnetometry by actively canceling technical noise sources like MW phase and power fluctuations.
- Solid-State Qubit Control: Applicable to other spin defects (SiC, h-BN) for advanced qubit control and quantum sensing protocols.
- Biomedical and Chemical Analysis:
- Nanoscale NMR Spectroscopy: Mitigating strong background signals (e.g., from the diamond spin bath) in nanoscale NMR experiments, improving the detection limit for target spins.
- Single-Cell Studies: Providing a fast, camera-free method for nuclear magnetic resonance spectroscopy in single-cell environments (e.g., microfluidic platforms).
- High-Speed Imaging and Microscopy:
- Accelerated Scanning: Replacing slow mechanical or galvanic scanning methods with AOM-based inertia-free scanning, accelerating data acquisition by hundreds of times in T1-limited imaging scenarios.
- Cost-Effective Imaging: Offering a straightforward alternative to complex, expensive, high-speed cameras for multipixel imaging applications.
- RF and Microwave Engineering:
- Affordable Source Integration: The demonstrated ability to cancel MW phase noise allows for the use of more affordable, lower-quality signal sources (AWGs) in future quantum experiments without sacrificing sensitivity.
View Original Abstract
Optically active solid-state spin systems have been extensively studied in quantum technologies. We introduce a new readout scheme, termed âtime-to-spaceâ (T2S) encoding, which decouples spin manipulation from optical readout both temporally and spatially. This is achieved by simultaneously controlling the spin state within a region of interest, followed by rapid scanning of the optical readout position using an acousto-optic modulator. Time tracking allows the optical readout position to be encoded as a function of time. Using nitrogen-vacancy center ensembles in diamond, we demonstrate that the T2S scheme enables correlated experiments for efficient common-mode noise cancellation in various nano- and microscale sensing scenarios. Additionally, we show scalable multipixel imaging that does not require a camera and has the potential to accelerate data acquisition by several hundred times compared to conventional scanning methods. We anticipate widespread adoption of this technique, as it requires no additional components beyond those commonly used in experiments with optically adressable spin systems.