| Metadata | Details |
|---|
| Publication Date | 2025-10-28 |
| Authors | Ankita Chakravarty, Romain Ruhlmann, Vincent Halde, David Roy-Guay, Michel Pioro-Ladrière |
| Analysis | Full AI Review Included |
- Core Value Proposition: Triple-tone microwave (MW) control is demonstrated as a practical strategy to mitigate the threefold sensitivity loss inherent in 14N Nitrogen-Vacancy (NV) ensemble magnetometers due to hyperfine splitting.
- Pulsed ODMR Enhancement: For Pulsed Optically Detected Magnetic Resonance (ODMR), triple-tone driving achieved up to a factor of three enhancement in signal slope, making it highly effective for samples exhibiting long coherence (low-dephasing regime).
- Ramsey Interferometry Trade-Offs: In Ramsey interferometry, triple-tone excitation only provided a sensitivity advantage when the MW power was limited (low Rabi frequency regime).
- High Power Regime: When high MW power is accessible, single-tone Ramsey protocols become highly sensitive and reliable, often matching or exceeding triple-tone performance, despite the resulting complex signal interference.
- Implementation: The technique requires no additional optical or RF hardware, relying solely on frequency modulation via IQ mixing, making it ideal for compact, field-deployable quantum sensors (e.g., the SBQuantum Quantum Demonstrator platform).
- Guidance for Engineers: The results delineate specific operating regimes, clarifying that triple-tone control is most beneficial for ODMR or power-limited Ramsey applications, while high-power single-tone is preferred otherwise.
| Parameter | Value | Unit | Context |
|---|
| Zero-Field Splitting (D) | 2.87 | GHz | NV ground state Hamiltonian |
| 14N Hyperfine Splitting (A||) | 2.16 | MHz | Separation between spin transitions |
| Diamond Sample Type | DNV-B1 (Element Six) | N/A | Single-crystal diamond |
| Sample Dimensions | 1 x 1 x 0.5 | mm3 | Volume of the diamond sample |
| NV Concentration | 300 | ppb | Nitrogen-Vacancy ensemble density |
| T2 Coherence Time | 1 | µs | Measured coherence time of the sample |
| Laser Excitation Wavelength | 520 | nm | Green laser used for optical initialization |
| Intermediate Frequency (fIF) | 100 | MHz | Used in IQ mixer for MW generation |
| ODMR Slope Ratio (Triple/Single) | 2.93 ± 0.09 | N/A | Experimental sensitivity ratio (Slope metric) |
| ODMR Slope/sqrt(T) Ratio | 2.28 ± 0.05 | N/A | Experimental sensitivity ratio (Slope/sqrt(T) metric) |
| Ramsey Revival Time | 463 | ns | Corresponds to 1/A|| |
- Integrated System Deployment: The experiment utilized a fully integrated NV magnetometry system (Quantum Demonstrator, SBQuantum) housing the diamond sample, a 520 nm laser, and a dual-post re-entrant microwave cavity, ensuring a compact footprint.
- MW Pulse Synthesis: Microwave pulses were generated using a Keysight PXIe chassis containing an Arbitrary Waveform Generator (AWG) and a high-speed digitizer. The AWG produced in-phase (I) and quadrature (Q) signals at a 100 MHz Intermediate Frequency (fIF).
- Frequency Upconversion: The I/Q signals were mixed with a Local Oscillator (LO) using an IQ mixer to generate the final amplified MW drive signal (fMW).
- Triple-Tone Control Implementation: Triple-tone excitation was achieved by programming the AWG to output three simultaneous tones separated by the 14N hyperfine splitting (2.16 MHz), without requiring external RF hardware.
- Pulsed ODMR Measurement: The protocol involved optical initialization, followed by a resonant π-pulse (single or triple-tone), and subsequent optical readout via fluorescence detection. Sensitivity was determined by fitting the ODMR spectra and extracting the maximum signal slope (dC/dv).
- Ramsey Interferometry Measurement: The sequence consisted of two π/2 pulses separated by a free evolution time (τ). The second pulse was phase-shifted by π/2. Triple-tone pulses were applied such that each tone received a π/2 phase shift in the second pulse.
- Numerical Modeling and Optimization: Experimental data was validated against a Lindblad master equation model for an effective spin-1/2 system. This model was used to simulate sensitivity landscapes across various Rabi frequencies and dephasing rates (γ), optimizing sensitivity metrics (slope and slope/sqrt(T)) for both single- and triple-tone protocols.
- Portable Quantum Sensing: Direct application in compact, power-limited NV magnetometers designed for field use, where maximizing sensitivity without increasing hardware complexity is critical.
- High-Sensitivity DC Magnetometry: Enhancing the signal-to-noise ratio in NV ensemble sensors used for detecting static magnetic fields in applications like wide-field imaging.
- Geophysical Surveying: Improving the performance of quantum diamond microscopes used for micrometer-scale magnetic imaging of geological samples.
- Biomedical Diagnostics: Applicable in systems requiring high-sensitivity magnetic field detection under ambient conditions, such as magnetocardiography or nanoscale sensing in biological environments.
- Quantum Control Systems: The demonstrated multi-frequency control techniques provide a robust, hardware-efficient method for coherent spin manipulation, relevant for optimizing pulse sequences in general quantum computing or sensing platforms utilizing solid-state defects.
View Original Abstract
Ensembles of nitrogen-vacancy (NV) centers in diamond are a well-established platform for quantum magnetometry under ambient conditions. One challenge arises from the hyperfine structure of the NV, which, for the common $^{14}$N isotope, results in a threefold reduction of contrast and thus sensitivity. By addressing each of the NV hyperfine transitions individually, triple-tone microwave (MW) control can mitigate this sensitivity loss. Here, we experimentally and theoretically investigate the regimes in which triple-tone excitation offers an advantage over standard single-tone MW control for two DC magnetometry protocols: pulsed optically detected magnetic resonance (ODMR) and Ramsey interferometry. We validate a master equation model of the NV dynamics against ensemble NV measurements, and use the model to explore triple-tone vs single-tone sensitivity for different MW powers and NV dephasing rates. For pulsed ODMR, triple-tone driving improves sensitivity by up to a factor of three in the low-dephasing regime, with diminishing gains when dephasing rates approach the hyperfine splitting. In contrast, for Ramsey interferometry, triple-tone excitation only improves sensitivity if MW power is limited. Our results delineate the operating regimes where triple-tone control provides a practical strategy for enhancing NV ensemble magnetometry in portable and power-limited sensors.