Single spin optically detected magnetic resonance with 60–90 GHz (E-band) microwave resonators

At a Glance

Metadata	Details
Publication Date	2015-06-01
Journal	Review of Scientific Instruments
Authors	Nabeel Aslam, Matthias Pfender, Rainer Stöhr, Philipp Neumann, Marc Scheffler
Institutions	University of Stuttgart, University of Tsukuba
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Field NV-ODMR Diamond Substrates

This document analyzes the requirements and achievements detailed in the research paper, “Single Spin Optically Detected Magnetic Resonance with E-Band Microwave Resonators,” and maps them directly to 6CCVD’s advanced MPCVD diamond capabilities, focusing on material solutions for high-frequency quantum sensing and spin control applications.

Executive Summary

Application Focus: Demonstration of single electron and nuclear spin optically detected magnetic resonance (ODMR) using Nitrogen-Vacancy (NV) centers in diamond at high magnetic fields (up to 3 T) and E-band microwave (MW) frequencies (71-76 GHz).
Core Innovation: Development of custom MW resonators (TM₁₁₀ cavity and tapered Coplanar Waveguide, CPW) integrated with optical access to achieve high MW-to-magnetic-field conversion efficiency.
Material Requirement: Ultra-high purity, low-strain Type-IIa diamond substrate, precisely oriented (111), and fabricated into thin, highly polished plates (90 µm thickness).
Performance Metrics: Achieved high MW efficiency (up to 27.0 MHz/√W) enabling coherent spin control (Rabi oscillations) at E-band frequencies.
Quantum Advancement: Demonstrated single-shot readout of the ¹⁴N nuclear spin with longitudinal relaxation times (T₁) on the order of seconds at 2.78 T, validating the use of high fields for improved quantum registers.
6CCVD Value Proposition: 6CCVD provides the necessary high-purity, low-nitrogen Single Crystal Diamond (SCD) substrates, custom dimensions (down to 90 µm thickness), precise (111) orientation, and integrated metalization required to replicate and advance this high-frequency quantum research.

Technical Specifications

The following hard data points were extracted from the experimental results and material parameters:

Parameter	Value	Unit	Context
Maximum Bias Magnetic Field (B)	3	T	Main superconducting magnet capability
MW Frequency Range (E-Band)	71 to 76	GHz	Used for electron spin manipulation
NV Zero Field Splitting (D)	2.87	GHz	Intrinsic NV property
Electron Spin Splitting Factor	2.28	MHz/mT	ms = ±1 level splitting
Maximum MW Efficiency (CRabi)	27.0	MHz/√W	Measured for CPW Resonator #2
MW Efficiency (Cmag)	1.36	mT/√W	Equivalent magnetic field conversion
¹⁴N Nuclear Spin T₁ Time	Second-long	N/A	Measured at 2.78 T during single-shot readout
Diamond Substrate Orientation	(111)	N/A	Optimized for NV alignment
Final Diamond Thickness	90	µm	Laser-cut and polished thin film
Substitutional Nitrogen Concentration	11	ppb	Purity of initial Type-IIa HPHT crystal
Electron Irradiation Dose	2 * 10¹⁰	e/cm²	Used for NV creation (2 MeV electrons)
CPW Resonator Dielectric Material	Rogers Ultralam 3850	N/A	Relative dielectric constant ɛ = 2.9

Key Methodologies

The experiment relied on precise material preparation and custom high-frequency component fabrication:

Substrate Selection and Orientation: A low-strain Type-IIa HPHT diamond crystal with ultra-low substitutional nitrogen (11 ppb) was selected. The crystal was oriented along the (111) axis to align NV centers with the surface normal, optimizing the ODMR setup.
NV Center Creation: NV centers were generated by irradiating the diamond plate with 2 MeV electrons (dose of 2 * 10¹⁰ e/cm²) followed by high-temperature annealing at 1000 °C for 2 hours in vacuum.
Custom Thin Film Fabrication: The resulting diamond was laser-cut and polished to a final dimension of 1 mm x 1 mm x 90 µm.
Microwave Delivery: E-band MW (71-76 GHz) was guided via rectangular WR-12 waveguides.
Resonator Design (TM₁₁₀ Cavity): A three-dimensional circular TM₁₁₀ cavity was designed using copper components, featuring a small hole for inductive coupling to the waveguide and a 525 µm hole for optical access.
Resonator Design (CPW Transition): A waveguide-to-tapered CPW resonator transition was fabricated on a double-sided printed circuit board (Rogers Ultralam 3850), utilizing a patch antenna for capacitive coupling and spatial field confinement, achieving a waist width down to 3 µm.
RF Nuclear Spin Control: Coherent control of the ¹⁴N nuclear spin was achieved by delivering radio-frequency (RF) fields via a 50 µm copper wire placed across the diamond surface on top of the CPW resonator.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials and fabrication services necessary to replicate and extend this high-field ODMR research, particularly by offering superior purity and custom integration capabilities.

Applicable Materials

To achieve the high coherence and long T₁ times demonstrated in this work, the highest quality diamond is essential.

Research Requirement	6CCVD Solution	Technical Advantage
High Purity, Low Strain (11 ppb N)	Optical Grade SCD (MPCVD)	Our MPCVD growth process routinely achieves nitrogen concentrations significantly below 5 ppb, minimizing decoherence sources (e.g., P1 centers) and ensuring superior material homogeneity compared to HPHT.
Specific Orientation ((111) surface)	Custom Oriented SCD Wafers	We provide high-quality SCD plates and wafers precisely oriented to (111) or other custom crystallographic directions, crucial for maximizing NV alignment efficiency in high-field setups.
NV Precursor Material (Type-IIa)	High-Purity SCD Substrates	Ideal starting material for controlled NV creation via ion implantation or electron irradiation, ensuring low background defects and high yield of desired NV charge states.

Customization Potential

The success of this experiment hinges on integrating the diamond into complex, high-frequency structures (CPW and cavity resonators). 6CCVD specializes in the required post-processing and integration steps.

Research Requirement	6CCVD Custom Capability	Engineering Relevance
Thin Film Fabrication (90 µm thickness)	Custom Thickness SCD Plates	We offer SCD wafers and plates polished to precise thicknesses ranging from 0.1 µm up to 500 µm, with custom dimensions up to 125 mm (PCD).
Ultra-Smooth Surfaces (Required for low loss)	Precision Polishing	Our SCD polishing achieves surface roughness Ra < 1 nm, minimizing scattering losses and ensuring optimal contact for integrated resonators.
Integrated Resonator Fabrication (Cu wire, CPW structures)	Internal Metalization Services	We offer in-house deposition of critical metals used in resonator design, including Au, Pt, Pd, Ti, W, and Cu. This capability allows for direct fabrication of CPW structures or contact pads onto the diamond surface, reducing conductive losses.
Optical Access Holes (525 µm diameter)	Precision Laser Cutting & Etching	Custom laser cutting and etching services allow for the creation of precise features, such as optical access holes or complex geometries required for coupling to E-band waveguides.

Engineering Support

6CCVD’s in-house PhD team provides comprehensive support for quantum and high-frequency applications:

Material Selection: Assistance in selecting the optimal SCD grade (e.g., isotopic purity, nitrogen concentration) for specific quantum sensing or quantum register projects.
NV Engineering Consultation: Guidance on optimizing post-growth processing parameters (irradiation dose, annealing temperature, and atmosphere) to maximize NV yield and coherence.
Integration Support: Expertise in designing and implementing metalization schemes (e.g., Ti/Pt/Au stacks) that are compatible with high-frequency MW environments and subsequent bonding or fabrication steps.

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

View Original Abstract

Magnetic resonance with ensembles of electron spins is commonly performed around 10 GHz, but also at frequencies above 240 GHz and in corresponding magnetic fields of over 9 T. However, experiments with single electron and nuclear spins so far only reach into frequency ranges of several 10 GHz, where existing coplanar waveguide structures for microwave (MW) delivery are compatible with single spin readout techniques (e.g., electrical or optical readout). Here, we explore the frequency range up to 90 GHz, with magnetic fields of up to ≈3 T for single spin magnetic resonance in conjunction with optical spin readout. To this end, we develop MW resonators with optical single spin access. In our case, rectangular 60-90 GHz (E-band) waveguides guarantee low-loss supply of microwaves to the resonators. Three dimensional cavities, as well as coplanar waveguide resonators, enhance MW fields by spatial and spectral confinement with a MW efficiency of 1.36mT/W. We utilize single nitrogen vacancy (NV) centers as hosts for optically accessible spins and show that their properties regarding optical spin readout known from smaller fields (&lt;0.65 T) are retained up to fields of 3 T. In addition, we demonstrate coherent control of single nuclear spins under these conditions. Furthermore, our results extend the applicable magnetic field range of a single spin magnetic field sensor. Regarding spin based quantum registers, high fields lead to a purer product basis of electron and nuclear spins, which promises improved spin lifetimes. For example, during continuous single-shot readout, the 14N nuclear spin shows second-long longitudinal relaxation times.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4922664