Phase-sensitive quantum spectroscopy with high-frequency resolution
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-30 |
| Journal | Physical review. A/Physical review, A |
| Authors | Nicolas Staudenmaier, Simon Schmitt, Liam P. McGuinness, Fedor Jelezko |
| Institutions | Center for Integrated Quantum Science and Technology, Australian National University |
| Citations | 20 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a novel quantum spectroscopy protocol, High Frequency Qdyne, utilizing a single Nitrogen-Vacancy (NV) center in diamond to achieve high spectral resolution for oscillating magnetic fields at the nanoscale.
- Core Achievement: Full signal reconstruction (phase, amplitude, frequency) of near-resonant fields up to potentially 100 GHz, overcoming the typical trade-off between spatial and spectral resolution in quantum sensors.
- Sensitivity Benchmark: Achieved an amplitude sensitivity of 58 nT/âHz and a phase sensitivity of 0.095 rad/âHz (at T = 1s integration).
- Frequency Resolution: Demonstrated a relative frequency uncertainty of 10-12 for a 1.51 GHz signal within 10 seconds of integration, achieving precision less than 1 mHz.
- Methodology: The protocol functions as an atomic heterodyne detector, down-converting high-frequency signals into a low-frequency beat-note within the detectorâs readout bandwidth.
- Dynamic Range: The full dynamic range spans from 58 nT/âHz (minimum detectable field) up to 360 nT (maximum field for optimal sensing time, Ï = 25 ”s).
- Material Basis: Utilizes single NV centers in highly purified 12C diamond (T2* up to 50 ”s) for nanoscale spatial resolution.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Amplitude Sensitivity | 58 | nT/âHz | At 1s integration time. |
| Phase Sensitivity | 0.095 | rad/âHz | Measured performance. |
| Frequency Uncertainty (Relative) | < 10-12 | Dimensionless | For 1.51 GHz signal, 10s integration. |
| Frequency Precision | < 1 | mHz | Achieved after 10s integration time. |
| Frequency Uncertainty Scaling | T-3/2 | Dimensionless | Dependence on total measurement time (T). |
| NV Gyromagnetic Ratio (ÎłNV) | 2Ï x 28.03 | MHz/mT | Used for magnetic field calibration. |
| NV Dephasing Time (T2*) | Up to 50 | ”s | Achieved using 99.999% 12C diamond. |
| Operating Frequency Range (Static B-field) | 1 to 5 | GHz | Requires static fields up to 70 mT. |
| Operating Frequency Range (High Field) | Up to 100 | GHz | Requires 3.5 T external magnetic field. |
| Dynamic Range (Upper Limit, Optimal Ï) | 0.36 | ”T | Corresponds to a Ï/2 rotation within Ï = 50 ”s. |
| Diamond Overgrowth Layer | ~100 | nm | Isotopically purified 12C layer thickness. |
| AWG Timing Resolution | 20 | ps | Arbitrary Waveform Generator (AWG70001A). |
| DC Shift Field Strength | 1 | Gauss | Used to shift resonance by -3 MHz during preparation/readout. |
Key Methodologies
Section titled âKey MethodologiesâThe High Frequency Qdyne protocol is a quantum analogue of classical heterodyne detection, tailored for single-spin sensors like the NV center.
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Sensor Preparation and Initialization:
- The NV center spin is polarized into the |0> state using a 532 nm green laser.
- A static magnetic field (up to 50 mT) is applied along the NV axis to tune the spin transition frequency (Vsens) close to the signal frequency (Vsig).
- A resonant Ï/2-pulse (control pulse, phase set to zero) prepares the NV spin in the superposition state |+i>.
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Sensing and Interaction (Ï period):
- The NV center is exposed to the near-resonant AC magnetic signal field (B(t)) for a fixed interaction time, Ï (e.g., 1404 ns).
- To prevent signal deterioration from continuous fields, a DC magnetic field shift (e.g., 1 Gauss, shifting resonance by 3 MHz) is applied during the preparation and readout phases, and turned OFF only during the sensing period Ï.
- The spin state evolves under the combined action of the signal field and the local oscillator (LO) phase.
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Local Oscillator (LO) Definition:
- The LO frequency (VLO) is defined by the sequence repetition rate (1/TL) and is synchronized with the measurement rate.
- VLO is set to be close to Vsens, ensuring the beat-note frequency (ÎŽ0 = Vsig - VLO) is low enough for detection.
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Readout and Data Acquisition:
- The final spin population is read out optically by collecting spin-dependent fluorescence (APD detection).
- The measurement sequence (duration TL) is repeated many times, sampling the spin population at fixed time intervals.
- The outcome probability oscillates at the beat-note frequency ÎŽ0.
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Signal Reconstruction:
- A Discrete Fast Fourier Transform (FFT) is performed on the sampled data (fluorescence count trace) to reveal the beat-note frequency ÎŽ0.
- The frequency, amplitude, and phase of the original Vsig signal are reconstructed by fitting the peak in the FFT spectrum using a Lorentzian function.
- Frequency uncertainty scales as T-3/2, allowing high resolution limited only by the stability of the external clock timing the AWG.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to perform high-resolution spectrum analysis at the nanoscale opens doors for several advanced engineering and quantum technology applications:
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Quantum Technologies and Computing:
- Characterization and diagnostics of miniaturized electric circuits and high-frequency components in quantum processors (e.g., superconducting qubits).
- Detection of single electron spins (ESR) and spin waves (magnons) in novel magnetic materials.
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Spectroscopy and Materials Science:
- Nanoscale Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy of single molecules and nuclei, providing structural and spatial information.
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Sensing and Metrology:
- Development of highly stable time and frequency standards.
- High-resolution velocimetry using Doppler Radar detection, capable of resolving velocities down to a few ”m/s in nano- to microscale settings due to high spectral resolution.
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RF and Microwave Engineering:
- Wide bandwidth instantaneous radio frequency spectrum analysis, potentially covering up to 100 GHz, for characterizing complex RF environments and devices.
View Original Abstract
Classical sensors for spectrum analysis are widely used but lack micro- or nanoscale spatial resolution. On the other hand, quantum sensors, capable of working with nanoscale precision, do not provide precise frequency resolution over a wide range of frequencies. Using a single spin in diamond, we present a measurement protocol for quantum probes which enables full signal reconstruction on a nanoscale spatial resolution up to potentially 100 GHz. We achieve 58nT/âHz amplitude and 0.095rad/âHz phase sensitivity and a relative frequency uncertainty of 10â12 for a 1.51 GHz signal within 10 s of integration. This technique opens the way to quantum spectrum analysis methods with potential applications in electron spin detection and nanocircuitry in quantum technologies.