Nanoscale Electrometry Based on a Magnetic-Field-Resistant Spin Sensor

At a Glance

Metadata	Details
Publication Date	2020-06-19
Journal	Physical Review Letters
Authors	Rui Li, Fei Kong, Pengju Zhao, Cheng Zhi, Zhuoyang Qin
Institutions	CAS Key Laboratory of Urban Pollutant Conversion, University of Science and Technology of China
Citations	43
Analysis	Full AI Review Included

Executive Summary

This research demonstrates a robust, magnetic-field-resistant method for nanoscale electrometry using Nitrogen-Vacancy (NV) centers in diamond, leveraging Continuous Dynamic Decoupling (CDD).

Core Innovation: The NV center is operated in a “dressed-state” space created by continuous microwave driving (CDD), rendering the sensor insensitive to magnetic fields (Zeeman effect and magnetic noise) while preserving sensitivity to electric fields (Stark effect).
Magnetic Resistance: The transition frequencies between dressed states show zero first-order dependence on the magnetic field, effectively suppressing ubiquitous magnetic noise near the diamond surface.
Electrometry Validation: The method successfully isolates electric noise, showing a clear linear dependence of energy levels on the applied electric field (voltage U), while remaining nearly constant with increasing magnetic current (I).
Quantitative Noise Study: The technique was used to unambiguously investigate surface electric noise by measuring the dephasing rate (1/T₂*) of near-surface NV centers (8 nm deep) covered by various liquids.
Key Finding: A quantitative inverse relationship was established between the dephasing rate and the dielectric permittivity (κ) of the covered liquid, providing insight into the electrostatic noise model near the diamond surface.
Noise Magnitude: The intrinsic electric noise magnitude (E²)^1/2 was estimated to be on the order of 10⁷ V/m.
Applicability: The method is robust against strong magnetic field inhomogeneity and fluctuation, and is applicable for detecting low-frequency electric noise (less than or equal to MHz).

Technical Specifications

Parameter	Value	Unit	Context
Zero-Field Splitting (D/h)	2.87	GHz	NV ground states
Axial Electric Dipole Moment (d_\|\|/h)	0.35 ± 0.02	Hz cm V^-1	Sensitivity to E_z
Non-Axial Electric Dipole Moment (d_⊥/h)	17 ± 3	Hz cm V^-1	Sensitivity to E_x, E_y
Gyromagnetic Ratio (γ)	28.03	GHz/T	Electron spin
NV Depth (Electrometry Demo)	~8	µm	Deep NV center used for initial E-field measurement
NV Depth (Surface Noise Study)	~8	nm	Near-surface NV centers
Maximum Axial Magnetic Field Applied	~16	µT	Corresponds to ~450 kHz energy shift in lab frame
Rabi Frequency (Ω₁)	50	MHz	Used for noise measurement (Fig 3)
Phase Modulation (Ω₂)	10	MHz	Used for noise measurement (Fig 3)
Diamond Dielectric Permittivity (κ_d)	5.7	N/A	Used in electrostatic noise model
Intrinsic Electric Noise Magnitude (E²)^1/2	Order of 10⁷	V/m	Estimated from dephasing rate
Noise Floor Dephasing Rate (1/T₂*)	~200	kHz	Measured noise floor in dressed state
Temperature Fluctuation (Home-built incubator)	Within 10	mK	Near the diamond sample

Dielectric Permittivities of Covered Liquids (κ)

Liquid	Dielectric Permittivity (κ)
Silicone Oil	2.56
1-Octanol	9.86
2,3-Butanediol	21.28
Glycerol	42
Propylene Carbonate (PC)	64

Key Methodologies

The experiment relies on precise sample preparation, advanced microwave control, and robust temperature stabilization to isolate the electric field effects.

Diamond Preparation:
- Electronic-grade diamonds were synthesized via Chemical Vapor Deposition (CVD).
- Deep NV Centers (Electrometry): Created during the CVD synthesis process (~8 µm depth).
- Near-Surface NV Centers (Noise Study): Created by ¹⁴N⁺ implantation (5 keV and 70 keV energies) with a dose density of 1 x 10⁹ cm^-2, resulting in ~8 nm and ~85 nm depths.
- Annealing: Samples were annealed at 1000 °C post-implantation.
- Optical Enhancement: A microscopic Solid-Immersion-Lens (SIL) was etched onto the surface above the NV center using Focused Ion Beam (FIB) milling to enhance photoluminescence collection.
Experimental Setup and Control:
- Confocal Microscopy: A home-built confocal microscope was used for NV manipulation and readout, utilizing a 532-nm laser and a Single Photon Counting Module (SPCM).
- Microwave System: Signals were generated by an Arbitrary Wave Generator (AWG), amplified, and delivered via a waveguide.
- Field Generation: Electric fields (E) were generated by applying voltage (U) across electroplated electrodes on the diamond surface. Magnetic fields (B) were generated by supplying current (I) to an external coil.
- Temperature Stabilization: Two incubators were used; the inner, home-built incubator maintained temperature fluctuation near the diamond surface within 10 mK.
Continuous Dynamic Decoupling (CDD) Sequence:
- The NV center was initialized to the |0> state via laser polarization.
- A microwave pulse chain (Initialization) prepared the spin into a superposition state (e.g., (| + 1> + |0>)/√2 in the lab frame, which is |+1> in the dressed frame).
- The Continuous Drive (CDD) field (H₁) was applied for duration t, creating the magnetic-field-resistant dressed-state space.
- The spin evolved, accumulating a phase proportional only to the electric field components.
- A reversed microwave pulse chain (Readout) transformed the accumulated phase into population differences, which were then read out via photoluminescence.
Noise Analysis:
- The dephasing rate (1/T₂*) was measured for near-surface NV centers covered by five different liquids with known dielectric permittivities (κ).
- The results were fitted using an electrostatic model relating 1/T₂* to the intrinsic noise (E²_int) and the surface noise (E²_surf), scaled by the dielectric constant of the covering liquid.

Commercial Applications

This magnetic-field-resistant electrometry technique is crucial for applications requiring high-sensitivity electric field detection in complex, noisy environments.

Quantum Computing and Sensing:
- Characterization and mitigation of charge noise in solid-state quantum chips (e.g., silicon carbide or diamond-based devices) where feature sizes are shrinking to the nanoscale.
- In situ monitoring of electric field fluctuations in quantum devices during operation.
Semiconductor and Microelectronics Industry:
- Nanoscale characterization of electrical properties and dynamics in modern electronic devices (e.g., semiconductor transistors) where surface charge fluctuations are critical.
- Imaging and sensing of single charges on surfaces with high spatial resolution.
Materials Science and Dielectric Characterization:
- Quantitative investigation of electric noise models near material interfaces.
- Nanoscale dielectric sensing and imaging, particularly for characterizing thin films or liquids in confined geometries.
Multiferroic Materials Research:
- Characterization of multiferroic materials where strong magnetic field inhomogeneity or fluctuation is common, allowing for selective study of electric polarization dynamics.

View Original Abstract

The nitrogen-vacancy (NV) center is a potential atomic-scale spin sensor for electric field sensing. However, its natural susceptibility to the magnetic field hinders effective detection of the electric field. Here we propose a robust electrometric method utilizing continuous dynamic decoupling (CDD) technique. During the CDD period, the NV center evolves in a dressed frame, where the sensor is resistant to magnetic fields but remains sensitive to electric fields. As an example, we use this method to isolate the electric noise from a complex electromagnetic environment near diamond surface via measuring the dephasing rate between dressed states. By reducing the surface electric noise with different covered liquids, we observe an unambiguous relation between the dephasing rate and the relative dielectric permittivity of the liquid, which enables a quantitative investigation of electric noise model near the diamond surface.

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevlett.124.247701