Optically induced static magnetic field in ensemble of nitrogen-vacancyn centers in diamond

At a Glance

Metadata	Details
Publication Date	2022-05-06
Journal	arXiv (Cornell University)
Authors	Farid Kalhor, Noah Opondo, Shoaib Mahmud, Leif Bauer, Li‐Ping Yang
Institutions	Northeast Normal University, Purdue University West Lafayette
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Optically Induced Static Magnetic Fields in NV Diamond

Executive Summary

This research demonstrates a critical step toward all-optical coherent control of spin qubits by utilizing the Photonic Spin Density (PSD) of an optical beam to induce an effective static magnetic field ($B_{\text{eff}}$) within bulk diamond NV ensembles.

Core Achievement: Successful demonstration of an optically induced static magnetic field proportional to the PSD, enabling coherent spin rotation on the Bloch sphere exceeding 10 degrees ($\phi \approx 12^\circ$).
Material Requirement: The experiment relies on high-quality, optical grade Single Crystal Diamond (SCD) substrates with (100) orientation to ensure minimal optical distortion and consistent NV center alignment.
Coherence Optimization: The Hahn echo pulse sequence was employed to maximize the NV ensemble coherence time ($T_2 \approx 42$ µs), crucial for achieving high measurement sensitivity.
On-Chip Integration: The platform uses E-beam lithography and custom Ti/Au metalization to fabricate integrated microwave antennas, paving the way for scalable on-chip quantum technologies.
Broadband Effect: The study characterized the wavelength dependence of $B_{\text{eff}}$ in the far off-resonant regime (705 nm to 818 nm), confirming the technique’s potential for broadband optical qubit control.
Application Focus: The results directly support the development of all-optical coherent spin qubit control, quantum sensing, and integrated quantum memories.

Technical Specifications

The following hard data points were extracted from the research paper, detailing the experimental parameters and results:

Parameter	Value	Unit	Context
Diamond Material Type	Optical Grade CVD Diamond	N/A	Bulk ensemble NV centers
Crystal Orientation	(100)	N/A	Used for consistent NV projection
Substrate Dimensions	4.5 x 4.5	mm	Platform for antenna fabrication
Maximum Effective Magnetic Field ($B_{\text{eff}}$)	60	nT	Achieved via PSD interaction
Maximum Spin Rotation Angle	$\approx 12$	degrees	Proportional to PSD
Coherence Time ($T_2$)	$\approx 42$	µs	Achieved using Hahn echo technique
Optimized Measurement Temperature	265	K	Used for $\lambda = 705$ nm measurements
PSD Laser Wavelengths Tested	705, 730, 785, 818	nm	Far off-resonant regime
Metalization Stack (Antenna)	Ti (30 nm) / Au (300 nm)	nm	Deposited via E-beam system
Stress-Release Etch Depth	5	µm	Performed on both sides of the plate

Key Methodologies

The experiment required precise material preparation and advanced quantum control techniques:

Substrate Preparation: Optical grade CVD diamond plates were cleaned using Piranha and Nitric acid soaks (30 minutes each), followed by solvent cleaning (Toluene, Acetone, Isopropanol) to ensure high surface purity.
Stress Etching: A 5 µm stress-release etch was performed on both sides of the diamond using an Inductively Coupled Plasma (ICP) etcher (Ar, O₂, and Cl₂ chemistry) to minimize strain.
E-beam Lithography: CSAR electron beam resist was applied, baked at 150 °C, and patterned using a JEOL JBX-8100 FS E-beam writer (30 pA current) to define the antenna structures.
Metalization: Following development and a 1-minute Ar/O₂ descum process, the microwave antennas were fabricated by depositing a 30 nm Titanium (Ti) adhesion layer followed by 300 nm of Gold (Au) using an electron beam metal deposition system.
Quantum Control: AC magnetometry was performed using the Hahn echo pulse sequence ($\pi/2_x - \tau - \pi_y - \tau - \pi/2_x$) to eliminate inhomogeneous broadening and maximize the coherence time $T_2$.
PSD Interaction: The effective static magnetic field was measured by adding the elliptically polarized PSD laser pulse to only one half of the Hahn echo sequence, inducing opposite spin rotations for subtraction and error elimination.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials and fabrication services required to replicate, optimize, and scale this research into integrated quantum devices.

Research Requirement (Paper)	6CCVD Solution & Capability	Value Proposition for Engineers
Optical Grade Diamond (Bulk SCD)	Single Crystal Diamond (SCD): High-purity, low-strain material optimized for NV center creation and high optical transparency.	Ensures minimal optical distortion and maximizes the intrinsic coherence time ($T_2$) of the NV ensemble.
Custom Dimensions (4.5 mm x 4.5 mm)	Custom Dimensions & Laser Cutting: Plates/wafers available up to 125 mm (PCD) and custom laser-cut SCD pieces.	Provides exact form factors needed for integration into specific on-chip quantum devices, eliminating the need for in-house dicing.
Surface Quality for E-beam Lithography	Ultra-Low Roughness Polishing: SCD polishing capability to Ra < 1 nm. Inch-size PCD polishing to Ra < 5 nm.	Essential for high-resolution E-beam lithography (as used for the 30 nm Ti layer) and minimizing surface scattering losses for integrated photonics.
Metalization Stack (Ti/Au Contacts)	In-House Metalization: Standard and custom stacks including Ti, Au, Pt, Pd, W, Cu.	Enables rapid prototyping of integrated microwave antennas and contacts (e.g., 30 nm Ti / 300 nm Au) required for ODMR and Hahn echo sequences.
Crystal Orientation (100)	Standard & Custom Orientations: SCD available in (100), (111), and (110) orientations.	Guarantees precise crystallographic alignment necessary for consistent bias magnetic field projection and optimized PSD interaction across all NV centers.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): High-purity, low-strain SCD substrates (Type IIa) with controlled nitrogen doping (ppm level) to ensure a uniform ensemble of NV centers.
Orientation: Standard (100) orientation, or custom (111) orientation for maximizing the projection of the NV axis onto the surface normal for specific quantum sensing applications.

Customization Potential

6CCVD offers comprehensive services to accelerate research and development:

Custom Dimensions: We can supply SCD plates in the exact 4.5 mm x 4.5 mm size used in the paper, or larger custom dimensions up to 125 mm (PCD).
Advanced Polishing: We provide polishing services to achieve Ra < 1 nm, critical for minimizing surface defects that affect E-beam lithography yield and optical performance.
Integrated Metalization: Our internal metalization capability allows for the deposition of the required Ti/Au stack directly onto the diamond substrate, streamlining the fabrication process for microwave antennas.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD growth and post-processing for quantum applications. We can assist researchers with material selection, NV creation protocols, and optimizing substrate specifications for similar all-optical coherent spin qubit control projects.

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

View Original Abstract

Generation of local magnetic field at the nanoscale is desired for many\napplications such as spin-qubit-based quantum memories. However, this is a\nchallenge due to the slow decay of static magnetic fields. Here, we demonstrate\nphotonic spin density (PSD) induced effective static magnetic field for an\nensemble of nitrogen-vacancy (NV) centers in bulk diamond. This locally induced\nmagnetic field is a result of coherent interaction between the optical\nexcitation and the NV centers. We demonstrate an optically induced spin\nrotation on the Bloch sphere exceeding 10 degrees which has potential\napplications in all optical coherent control of spin qubits.\n

Tech Support

Original Source

DOI: https://doi.org/10.1364/ol.460836