Skip to content
6CCVD Research

Multipoint Lock-in Detection for Diamond Nitrogen-Vacancy Magnetometry Using DDS-Based Frequency-Shift Keying

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-12-21
JournalMicromachines
AuthorsQidi Hu, Luheng Cheng, Yushan Liu, Xinyi Zhu, Yu Tian
InstitutionsHefei University of Technology, Zhejiang Lab
Citations1
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This analysis focuses on a novel, integrated digital system designed for multipoint lock-in detection in diamond Nitrogen-Vacancy (NV) center magnetometry.

  • Core Innovation: The system achieves multipoint lock-in detection using only a single, self-built microwave (MW) source, significantly reducing the complexity and integration challenges associated with traditional multi-source setups.
  • Key Technology: It employs a Direct Digital Synthesizer (DDS) combined with Frequency-Shift Keying (FSK) to enable rapid, arbitrary frequency hopping. This allows the system to encode an unlimited number of resonant points during sensing.
  • Performance Metrics: The DDS architecture supports a maximum frequency bandwidth of 1.4 GHz and achieves frequency shifting times at the sub-”s level, ensuring high data timeliness.
  • Synchronization: Synchronization between the MW source and the data acquisition (DAQ) module is achieved via a shared trigger signal, ensuring that the sampled fluorescence data is correctly associated with the current FSK-modulated frequency.
  • Multi-Resonance Detection: The method successfully tracks multiple NV resonance peaks simultaneously, enabling the observation of temperature and magnetic field fluctuations and providing a foundation for vector magnetometry.
  • Integration and Portability: The entire MW source and sampling module are integrated onto a small 60 mm × 50 mm PCB, making the system highly suitable for miniaturized and portable quantum sensing applications.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
DDS Maximum Bandwidth1.4GHzTheoretical limit for frequency hopping.
Practical MW Control Bandwidth>500MHzPractical operational range.
Frequency Shift TimeSub-”ssecondsMinimal time required for frequency shifting (DDS capability).
ADC Sampling Rate (Max)125MSPSMaster FPGA integrated ADC (LTC2145CUP-14).
ADC Resolution14bitData acquisition resolution.
ADC Full-Scale Range (FSR)1 or 20VSelectable via jumper.
Master FPGA Clock Frequency125MHzClock driving the sampling module.
MW Output Range (Down-converted)2.5 to 3.0GHzOperational range for NV ODMR experiments.
PLL Reference Clock (PLL1/PLL2)3.5GHzUsed for DDS reference and mixer Local Oscillator (LO) signal.
cw-ODMR Sweep Range2.8 to 2.95GHzFrequency range tested in the continuous wave ODMR experiment.
MW Power Level~17dBmOutput power used for NV excitation.
Lock-in Frequency Offset (foffset)500kHzFrequency deviation used for FSK modulation (total gap 1 MHz).
Magnetic Field Oscillation Frequency0.2HzFrequency of the sinusoidal AC field measured in lock-in detection.
PCB Dimensions60 × 50mm2Size of the integrated MW source and components.

Key Methodologies

Section titled “Key Methodologies”

The multipoint lock-in detection relies on synchronized DDS-based Frequency-Shift Keying (FSK) across the MW source, DAQ, and Digital Signal Processing (DSP) modules.

  1. Frequency Word Configuration: Frequency Turning Words (FTWs) and a Frequency Offset Word (FOW) are calculated and stored in the RAM of the Slave FPGA (Xilinx Artix-7). FTWs define the center frequencies (fcenter) of the resonance points to be tracked, while the FOW defines the lock-in modulation offset (foffset).
  2. FSK Modulation and Hopping: The DDS chip (AD9914) generates the MW signal. The frequency is modulated based on the level of a shared square-wave trigger signal:
    • High Level (Section A): Output frequency is fcenter + foffset.
    • Low Level (Section B): Output frequency is fcenter - foffset.
    • The system loops through the stored FTWs, causing the center frequency to hop arbitrarily across the spectrum for multipoint detection.
  3. MW Signal Conditioning: The DDS output is mixed with a 3.5 GHz LO signal (generated by PLL2) and down-converted to the required 2.5 GHz to 3.0 GHz range, then amplified and cleaned using a bandpass filter (BP).
  4. Synchronized Data Acquisition: The DAQ module (LTC2145CUP-14 ADC) samples the photodetector (PD) fluorescence signal. Sampling is synchronized with the trigger signal, operating only during defined “Detection Windows.”
  5. Delay Window Implementation: A “Delay Window” is inserted after each trigger edge (positive or negative) to allow the DDS time to settle to the new frequency (sub-”s shift time), preventing errors from transient signals.
  6. Data Encoding and Processing: The DSP module marks the accumulated 14-bit data as either Part A (fcenter + foffset) or Part B (fcenter - foffset) based on the current trigger level and packages the data into 128-bit packets with markers.
  7. Lock-in Calculation: Data frames are uploaded to the PC via UDP. The PC performs the final differential calculation (Δ = A - B) for each FTW point, extracting the oscillating fluorescence signal corresponding to the external magnetic field fluctuation.

Commercial Applications

Section titled “Commercial Applications”

The integrated DDS/FSK architecture provides significant advantages for applications requiring compact, high-speed, and multi-channel RF control in quantum systems.

  • Quantum Vector Magnetometry: Simultaneous tracking of multiple NV resonance groups (corresponding to different crystal orientations) allows for real-time determination of the direction and magnitude of external magnetic fields.
  • Portable Quantum Sensors: The highly integrated, small-footprint design (60 mm × 50 mm PCB) is ideal for developing miniaturized and highly mobile quantum detection equipment for field use (e.g., geological surveys, defense).
  • Quantum Computing and Simulation: The rapid, arbitrary frequency hopping capability is essential for controlling multiple qubits in quantum processors, where precise and fast MW pulses are required across a wide frequency spectrum.
  • Integrated RF Signal Generation: The DDS/FPGA platform serves as a high-performance, software-defined microwave source suitable for general precision measurement and spectroscopy systems requiring high frequency agility and stability.
  • Joint Environmental Sensing: Utilizing the NV center’s sensitivity to both magnetic fields and temperature, the system can be applied to simultaneous, localized monitoring of both parameters in complex environments.
  • Low-Frequency Signal Detection: While demonstrated at 0.2 Hz, the system’s architecture is optimized for high-sensitivity detection of low-frequency magnetic signals, relevant for biomagnetism or non-destructive testing.
View Original Abstract

In recent years, the nitrogen-vacancy (NV) center in diamonds has been demonstrated to be a high-performance multiphysics sensor, where a lock-in amplifier (LIA) is often adopted to monitor photoluminescence changes around the resonance. It is rather complex when multiple resonant points are utilized to realize a vector or temperature-magnetic joint sensing. In this article, we present a novel scheme to realize multipoint lock-in detection with only a single-channel device. This method is based on a direct digital synthesizer (DDS) and frequency-shift keying (FSK) technique, which is capable of freely hopping frequencies with a maximum of 1.4 GHz bandwidth and encoding an unlimited number of resonant points during the sensing process. We demonstrate this method in experiments and show it would be generally useful in quantum multi-frequency excitation applications, especially in the portable and highly mobile cases.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2020 - Sensitivity optimization for nv-diamond magnetometry [Crossref]
  2. 2020 - Efficient implementation of a quantum algorithm in a single nitrogen-vacancy center of diamond [Crossref]
  3. 2008 - Multipartite entanglement among single spins in diamond [Crossref]
  4. 2013 - Quantum logic readout and cooling of a single dark electron spin [Crossref]
  5. 2016 - Direct measurement of topological numbers with spins in diamond [Crossref]
  6. 2015 - Quantum simulation of helium hydride cation in a solid-state spin register [Crossref]
  7. 2008 - Nanoscale magnetic sensing with an individual electronic spin in diamond [Crossref]
  8. 2012 - High spatial and temporal resolution wide-field imaging of neuron activity using quantum nv-diamond [Crossref]
  9. 2017 - Measuring broadband magnetic fields on the nanoscale using a hybrid quantum register [Crossref]
  10. 2022 - Multiplexed sensing of magnetic field and temperature in real time using a nitrogen-vacancy ensemble in diamond [Crossref]

Reads Similar to This

Diamond Films for Implantable Electrodes Orientated growth the 3D diamond/graphene hybrid arrays and the application in thermal interface materials Nitrogen-vacancy ensemble magnetometry based on pump absorption