Nuclear spin metrology with nitrogen vacancy center in diamond for axion dark matter detection

At a Glance

Metadata	Details
Publication Date	2025-04-29
Journal	Physical review. D/Physical review. D.
Authors	So Chigusa, M. Hazumi, Ernst David Herbschleb, Yuichiro Matsuzaki, Norikazu Mizuochi
Institutions	Institute of Particle and Nuclear Studies, Kavli Institute for the Physics and Mathematics of the Universe
Citations	2
Analysis	Full AI Review Included

Technical Analysis: Nuclear Spin Metrology for Axion Dark Matter Detection

Document Reference: PHYSICAL REVIEW D 111, 075028 (2025) Application Focus: Quantum Sensing, Axion Dark Matter (DM) Detection, Nitrogen Vacancy (NV) Centers in Diamond

Executive Summary

This research proposes a novel quantum metrology approach using the nuclear spin of ¹⁴N Nitrogen Vacancy (NV) centers in diamond to detect axion dark matter (DM). This method offers complementary sensitivity to axion-nucleus couplings (g_ann, g_app) independent of conventional electron spin metrology.

Core Achievement: Direct detection method for axion DM leveraging the long coherence time (T_2N) of the ¹⁴N nuclear spin qubit, enabling nuclear spin magnetometry.
Target Physics: Constrains axion-neutron (g_ann) and axion-proton (g_app) couplings, crucial for differentiating axion models.
Frequency Range: Sensitive to a broad frequency range $\le$ 100 Hz (corresponding to axion mass m_a $\le$ 4 x 10^-13 eV) using the Ramsey sequence protocol.
Material Requirements: Requires high-quality, large-volume diamond substrates (up to 10mm thickness) with optimized NV center ensembles (N up to 10²⁰) and high creation yield (up to 25.8%).
Coherence Enhancement: Achieves high sensitivity by exploiting long nuclear spin coherence times (T_2N up to 7.25 ms at room temperature, prospectively 1 s in cryogenic/DD setups).
Customization Need: Success relies on advanced diamond fabrication, including controlled nitrogen isotopic doping (¹⁴N or ¹⁵N) and preferential NV center alignment (e.g., via (111) growth).

Technical Specifications

The following hard data points summarize the key physical parameters and experimental requirements detailed in the paper.

Parameter	Value	Unit	Context
Electron Spin Zero-Field Splitting ($\Delta$₀)	2$\pi$ x 2.87	GHz	NV Center System
Nuclear Quadrupole Interaction (Q₀)	-2$\pi$ x 4.95	MHz	¹⁴N NV Center System
Electron Gyromagnetic Ratio ($\gamma$_e)	2$\pi$ x 28	GHz/T	Conventional Magnetometry
Nuclear Gyromagnetic Ratio ($\gamma$_N)	2$\pi$ x 3.08	MHz/T	¹⁴N Isotope
Target Axion Mass Range (m_a)	$\le$ 4 x 10^-13	eV	Corresponds to frequency $\le$ 100 Hz
Maximum Detection Frequency (f)	$\le$ 200	Hz	Ramsey Sequence Limit (T_2N = 7.25 ms)
Required NV Ensemble Size (N)	10¹² to 10²⁰	Centers	Statistical Sensitivity Scaling
Room Temperature Nuclear Coherence (T_2N)	7.25	ms	Standard Ramsey Protocol
Optimized Cryogenic Coherence (T_2N)	1	s	Dynamic Decoupling (DD) Prospect
Required Sample Volume (N=10²⁰)	3 x 10⁹	Samples	Based on 1mm x 1mm x 70µm, 0.68% yield
Optimal Free Precession Time ($\tau$)	T_2N/2	N/A	Maximizes sensitivity in Ramsey sequence

Key Methodologies

The experiment relies on precise control of the NV center spin state using established quantum metrology protocols adapted for dark matter detection.

NV Center Preparation: Diamond substrates must be synthesized or treated to achieve high concentrations of nitrogen (¹⁴N or ¹⁵N) and subsequent vacancy creation, resulting in NV centers. High NV creation yield (up to 25.8% state-of-the-art) is critical for reaching N=10²⁰ ensembles.
Spin Initialization and Readout: The electron spin (S=1) is initialized via 532 nm green laser excitation and read out via fluorescence measurement (600-800 nm red light). Nuclear spin initialization (I=1) is achieved using CNOT gates.
Spin Manipulation (Rabi Cycle): Microwave (GHz) and radio frequency (MHz) pulses are applied to control the electron and nuclear spin states, leveraging the hyperfine interaction (A_|| $\approx$ -2$\pi$ x 2.16 MHz).
DC Axion Detection (Ramsey Sequence): The nuclear spin is allowed to freely precess for time $\tau$. This sequence is optimized for low-frequency, DC-like axion signals ($\epsilon \ll 1/\tau$).
AC Axion Detection (Hahn-Echo/DD Sequence): Used for narrow-band searches at higher frequencies ($\epsilon \approx 2\pi/\tau$). Dynamic Decoupling (DD) sequences (using N$_{\pi}$ pulses) are implemented to extend the transverse coherence time (T_2N) up to 1 s, significantly boosting sensitivity.
Data Analysis: The Power Spectral Density (PSD) of the measured fluorescence signal is calculated to identify resonant peaks corresponding to the axion mass (m_a).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate and extend this groundbreaking axion dark matter research. Our capabilities directly address the critical material challenges identified in the paper, particularly the need for large, high-quality, doped, and oriented substrates.

Applicable Materials

To achieve the required statistical sensitivity (N $\sim$ 10²⁰) and long coherence times (T_2N $\sim$ 1 s), researchers require the highest quality Single Crystal Diamond (SCD) with precise nitrogen control.

Material Requirement (Paper)	6CCVD Solution	Technical Advantage
High-Volume Substrates (for N $\sim$ 10²⁰)	Thick SCD Substrates (up to 10mm) or Large PCD Wafers (up to 125mm)	Enables the necessary detector volume to house large NV ensembles, reducing the total number of required samples.
Controlled Nitrogen Doping (¹⁴N or ¹⁵N)	Custom Doped SCD (MPCVD Growth)	We offer precise control over nitrogen concentration during growth, maximizing NV creation yield (up to 25.8% achievable via optimized CVD) and enabling isotopic purity control for specific coupling studies (e.g., ¹⁵N for g_app constraints).
NV Center Alignment (for reduced noise)	Optical Grade SCD on (111) Orientation	SCD grown on the (111) surface ensures perfect preferential orientation of NV centers, minimizing magnetic noise effects and maximizing signal coherence.
Long Coherence Time (T_2N $\sim$ 1 s)	High Purity SCD (Low Strain/Defect Density)	Our high-purity MPCVD growth minimizes lattice defects and strain, which are primary sources of decoherence, supporting the long T_2N required for high-sensitivity DD sequences.

Customization Potential

The experimental protocols require specialized interfaces for microwave and RF control. 6CCVD offers end-to-end fabrication services to meet these needs:

Custom Dimensions: While the paper references small 1mm x 1mm samples, achieving N=10²⁰ is far more practical using larger substrates. 6CCVD supplies SCD plates up to 10mm thick and PCD wafers up to 125mm in diameter, allowing for scalable detector designs.
Advanced Metalization: The Rabi cycle and DD sequences require precise microwave/RF delivery structures (e.g., coplanar waveguides). 6CCVD provides in-house metalization services (Au, Pt, Ti, W, Cu) directly onto the diamond surface, ensuring optimal coupling and minimal signal loss.
Surface Quality: To maintain high optical and spin fidelity, 6CCVD guarantees ultra-low roughness polishing (Ra $\lt$ 1 nm for SCD), essential for minimizing surface defects that contribute to decoherence.

Engineering Support

The successful implementation of nuclear spin metrology for axion detection is a complex engineering challenge. 6CCVD provides expert consultation to accelerate research timelines.

Material Selection and Optimization: Our in-house PhD team specializes in optimizing MPCVD growth parameters (pressure, temperature, gas flow) to maximize NV yield and control isotopic doping for similar Axion Dark Matter Detection projects.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of high-value, custom diamond materials, supporting international collaborations referenced in this paper.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We present a method to directly detect the axion dark matter using nitrogen vacancy centers in diamonds. In particular, we use metrology leveraging the nuclear spin of nitrogen to detect axion-nucleus couplings. This is achieved through protocols designed for dark matter searches, which introduce a novel approach of quantum sensing techniques based on the nitrogen vacancy center. Although the coupling strength of the magnetic fields with nuclear spins is three orders of magnitude smaller than that with electron spins for conventional magnetometry, the axion interaction strength with nuclear spins is the same order of magnitude as that with electron spins. Furthermore, we can take advantage of the long coherence time by using the nuclear spins for the axion dark matter detection. Our method has the potential to be sensitive to a broad frequency range <a:math xmlns:a=“http://www.w3.org/1998/Math/MathML” display=“inline”><a:mrow><a:mo>≲</a:mo><a:mn>100</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mrow><a:mi>Hz</a:mi></a:mrow></a:mrow></a:math> corresponding to the axion mass <c:math xmlns:c=“http://www.w3.org/1998/Math/MathML” display=“inline”><c:mrow><c:msub><c:mrow><c:mi>m</c:mi></c:mrow><c:mrow><c:mi>a</c:mi></c:mrow></c:msub><c:mo>≲</c:mo><c:mn>4</c:mn><c:mo>×</c:mo><c:msup><c:mrow><c:mn>10</c:mn></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>13</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:mtext> </c:mtext><c:mi>eV</c:mi></c:mrow></c:math>. We present the detection limit of our method for both the axion-neutron and the axion-proton couplings and discuss its significance in comparison with other proposed ideas. We also show that the sensitivities of the NV center sensor to various spin species will open up new directions for constructing protocols that can mitigate magnetic noise effects.

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevd.111.075028