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6CCVD Research

A robust fiber-based quantum thermometer coupled with nitrogen-vacancy centers

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-04-01
JournalReview of Scientific Instruments
AuthorsShao-Chun Zhang, Yang Dong, Bo Du, Hao-Bin Lin, Li Shen
InstitutionsUniversity of Science and Technology of China, Hefei National Center for Physical Sciences at Nanoscale
Citations35
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This analysis summarizes the development and performance of a robust, fiber-based quantum thermometer utilizing high-density Nitrogen-Vacancy (NV) centers in diamond.

  • Core Achievement: Demonstrated a quantum thermometer with a high sensitivity of 18 mK/√Hz at room temperature, specifically designed for robustness against common environmental noise.
  • Noise Isolation: The system successfully isolates temperature measurements from both external magnetic field noise (tested up to 5.2 ”T) and microwave (MW) power shifts (demonstrated 8 dB dynamic range).
  • Methodology: Robustness is achieved using a single lock-in measurement scheme where the MW center frequency (fc) is fixed precisely at the zero-crossing sharp-dip (f0) of the Frequency Modulated (FM) Optically Detected Magnetic Resonance (ODMR) spectrum.
  • Material: Utilizes a high-density NV ensemble ([N] ≈ 40 ppm) in a bulk diamond membrane coupled to a multi-mode optical fiber.
  • Practical Application: The device was successfully used to image the surface temperature distribution of a working electronic chip (Raspberry Pi Zero W).
  • Engineering Value: The compact, fiber-coupled design and inherent noise immunity represent a significant advance toward transitioning lab-based NV sensing systems into practical, real-world applications.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Temperature Sensitivity18mK/√HzAchieved using fc = f0 (zero-crossing).
Magnetic Sensitivity49nT/√HzMeasured using fc = f+1 (for comparison).
Noise Floor (System Limit)4mK/√HzLimited by lock-in input and detected shot noise (MW/Laser off).
NV Ensemble Density (Nitrogen)~40ppmConcentration of substitutional nitrogen ([N]).
NV- Density~0.15ppmConcentration of negatively charged NV centers.
Laser Wavelength532nmGreen excitation source.
Maximum Laser Power (Operational)< 10mWLimit set to minimize laser-heating effects on the diamond.
ODMR Zero-Field Frequency (ZFS)~2.87GHzCenter frequency of the sharp-dip structure.
Optimal MW Power Range22 - 27dBmDynamic range offering <10% sensitivity variation (8 dB range).
Optimal Modulation Deviation (fd)1.6 - 2MHzRange for best temperature sensitivity.
Thermal Equilibrium Time~100msTime required for the 200 x 200 ”m2 sensor to reach thermal equilibrium.
Test Magnetic Field (Noise Test)5.2”TOscillating at 1 Hz, successfully decoupled by the f0 method.
Diamond Membrane Size200 x 200 x 100”m3Dimensions of the bulk diamond attached to the fiber tip.

Key Methodologies

Section titled “Key Methodologies”

The robustness and sensitivity were achieved through a hybrid fiber-optic setup and optimized frequency modulation techniques on a high-density NV ensemble:

  1. Sensor Fabrication: A bulk diamond membrane (200 x 200 x 100 ”m3) containing a high-density NV ensemble ([N] ≈ 40 ppm) was mechanically polished and attached to the tip of a multi-mode optical fiber (100 ”m core diameter).
  2. Hybrid Fiber-Optic Setup: A 532 nm green laser was coupled into the fiber for continuous optical excitation. Photoluminescence (PL) was collected by the same fiber, filtered (647 nm long pass), and detected by a photodetector.
  3. Microwave (MW) Delivery: MW signals (2.87 GHz range) were generated, amplified (up to 27 dBm), and delivered via a five-turn copper loop antenna wound around the fiber ceramic plug core.
  4. Frequency Modulation (FM) ODMR: The MW frequency was sinusoidally modulated (F(t) ≈ fc + fdcos(2πfmodt)). The resulting AC signal was amplified and processed using a lock-in amplifier (LIA).
  5. Optimal Center Frequency Selection: The MW center frequency (fc) was precisely tuned to the zero-crossing point (f0) of the FM ODMR spectrum. This point corresponds to the maximum slope (|dU/df|max) and provides the largest temperature response.
  6. Noise Decoupling: By fixing fc at f0, the LIA signal becomes proportional only to the temperature shift (ΔT) and is decoupled from magnetic field noise (ΔB) and MW power shifts (ΔP), as confirmed by experimental tests.
  7. Temperature Imaging: The fiber-based sensor was scanned across the surface of a powered electronic chip. The LIA signal variation was recorded and directly converted into a surface temperature distribution map, demonstrating a maximum temperature of 26.5 °C on the chip surface.

Commercial Applications

Section titled “Commercial Applications”

The demonstrated robustness and high sensitivity of this fiber-based quantum thermometer make it suitable for deployment in environments where conventional NV sensing is hampered by noise.

  • Integrated Circuit (IC) Diagnostics: High-resolution, non-contact thermal imaging of microelectronic components (e.g., CPUs, GPUs, power electronics) for identifying localized hot spots, optimizing thermal dissipation, and performing failure analysis.
  • Biological and Medical Endoscopy: Use in compact, fiber-coupled probes for precise, localized temperature monitoring within biological systems or during minimally invasive surgical procedures, especially where magnetic fields (e.g., MRI environments) might be present.
  • Microfluidics and Chemical Sensing: Monitoring highly localized temperature changes in microreactors or lab-on-a-chip devices, critical for controlling chemical reaction kinetics or phase transitions.
  • Quantum Sensing in RF/EMI Environments: Deployment of NV sensors in industrial or complex electronic settings where fluctuating radio frequency (RF) fields or electromagnetic interference (EMI) typically degrade measurement accuracy.
  • Advanced Material Characterization: Measuring thermal properties and localized heating effects in novel materials or nanostructures under operational conditions.
View Original Abstract

The nitrogen-vacancy center in diamond has been broadly applied in quantum sensing since it is sensitive to different physical quantities. Meanwhile, it is difficult to isolate disturbances from unwanted physical quantities in practical applications. Here, we present a fiber-based quantum thermometer by tracking the sharp-dip in the zero-field optically detected magnetic resonance spectrum in a high-density nitrogen-vacancy ensemble. Such a scheme can not only significantly isolate the magnetic field and microwave power drift but also improve the temperature sensitivity. Thanks to its simplicity and compatibility in implementation and robustness, this quantum thermometer is then applied to the surface temperature imaging of an electronic chip with a sensitivity of 18mK/Hz. It thus paves the way to high sensitive temperature measurements in ambiguous environments.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2017 - High Sensitivity Magnetometers

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