Coherent control of NV− centers in diamond in a quantum teaching lab

At a Glance

Metadata	Details
Publication Date	2020-11-19
Journal	American Journal of Physics
Authors	Vikas K. Sewani, Hyma H. Vallabhapurapu, Yang Yang, Hannes R. Firgau, Chris Adambukulam
Institutions	UNSW Sydney, University of Melbourne
Citations	32
Analysis	Full AI Review Included

Technical Documentation & Analysis: Coherent Control of NV- Centers in Diamond

Executive Summary

This documentation analyzes the requirements and results of the research paper “Coherent control of NV^- centers in diamond in a quantum teaching lab,” focusing on material specifications and aligning them with 6CCVD’s advanced MPCVD diamond capabilities.

Core Achievement: Successful implementation of a low-cost, robust experimental setup for performing coherent control (Rabi, T₂ dynamical decoupling) on ensemble Nitrogen-Vacancy (NV^-) centers at room temperature.
Material Requirement: The experiments necessitate high-quality, single-crystal diamond (SCD) with a controlled NV^- concentration, achievable either through high-density HPHT or high-coherence CVD material.
Key Performance Metrics: Measured spin relaxation time (T₁) of 1.64 ± 0.25 ms and a driven coherence time (T_Rabi) of 1.12 ± 0.14 µs for the high-density HPHT sample.
Methodology: Utilizes pulsed Optically Detected Magnetic Resonance (ODMR) combined with a lock-in amplifier for high signal-to-noise ratio detection of low-contrast spin signals.
6CCVD Value Proposition: 6CCVD provides the necessary high-purity MPCVD SCD wafers in custom orientations ((100) or (111)) and with controlled nitrogen doping levels, essential for replicating high-signal teaching setups or advancing to long-coherence research applications.
Customization: The setup relies on a custom PCB antenna; 6CCVD offers custom metalization and precise laser cutting to facilitate integrated device fabrication and optimal B₁ field alignment.

Technical Specifications

The following hard data points were extracted from the experimental results and setup description:

Parameter	Value	Unit	Context
Zero-Field Splitting (D)	2.87	GHz	NV^- ground state
Spin Relaxation Time (T₁)	1.64 ± 0.25	ms	Measured using all-optical method (HPHT sample)
Rabi Frequency (Ω_R)	2.69 ± 0.02	MHz	Achieved with B₁ field
Driven Coherence Time (T_Rabi)	1.12 ± 0.14	µs	Limited by B₁ inhomogeneity and ensemble broadening
Hahn Echo Coherence Time (T_Hahn)	1.2 ± 0.2	µs	Free precession T₂ measurement
Excitation Wavelength (λ_exc)	520	nm	Green laser diode source
Zero-Phonon Line (ZPL)	637	nm	NV^- emission wavelength
MW Antenna Resonance (Measured)	~2.49	GHz	PCB antenna S₁₁ minimum
Maximum Oscillating B₁ Field	306	µT	Simulated at +24 dBm MW power
π/2 Pulse Length (τ_π/2)	72	ns	Calibrated from Rabi oscillations
Diamond Orientation (Used)	(111)	-	HPHT sample
Diamond Orientation (Alternative)	(100)	-	CVD sample comparison

Key Methodologies

The experimental success relies on precise material preparation and synchronized electronic control:

Material Selection and Processing: The primary sample was a (111)-oriented HPHT diamond, subjected to electron irradiation (10¹⁸ electrons/cm²) and annealing (900°C) to maximize NV^- concentration and signal strength, prioritizing signal over intrinsic coherence time.
Optical Setup: A fiber-coupled 520 nm green laser is focused to a ~1 µm spot using a 50x/0.80NA objective. PL emission is collected through a dichroic mirror and filtered (600 nm long pass, 900 nm short pass) to isolate the NV^- signal.
Microwave (MW) Delivery: A custom-designed PCB antenna (loop-gap resonator geometry) is placed between the objective and the diamond sample. It features a 1 mm hole for optical access and delivers the oscillating B₁ field perpendicular to the PCB plane.
Electronic Control: A Pulse Blaster (ESR Pro 250) generates synchronized TTL pulse sequences (4 channels) for laser modulation (CH1) and I/Q modulation of the MW signal (CH2, CH3), enabling precise control over the spin state evolution.
Signal Detection: A dual-phase lock-in amplifier is used, referenced to the pulse sequence frequency (CH0), to perform phase-sensitive measurement, extracting the low-contrast ODMR signal from the large background PL.
Coherent Pulsing: Implemented sequences include pulsed ODMR, Rabi oscillations (demonstrating coherent rotation), and dynamical decoupling (Hahn echo and CPMG) to measure and extend the spin coherence time (T₂).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and customization services required to replicate, optimize, and advance this quantum teaching lab setup into a cutting-edge research platform.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
High-Coherence Material	Optical Grade SCD (Low Nitrogen, < 1 ppb)	Essential for extending T₂ coherence times far beyond the 1.2 µs achieved with the high-density samples, enabling advanced quantum sensing and computing research.
High-Signal Material (Teaching Labs)	Controlled Nitrogen Doped SCD (1-5 ppm)	Provides the high ensemble NV^- density required for strong PL signal and short measurement times (as demonstrated by the HPHT sample), crucial for efficient undergraduate lab instruction.
Crystal Orientation	Custom (100) and (111) SCD Wafers	We supply both orientations. The paper notes that (100) orientation offers a 57.74% effective magnetic resonance drive efficiency, while (111) can be optimized for single-axis alignment, allowing researchers to select the optimal substrate for their B₁ field geometry.
Substrate Dimensions	Custom Plates/Wafers up to 125mm	We provide SCD plates up to 500 µm thick and substrates up to 10 mm, ensuring compatibility with custom antenna designs and large-scale optical setups.
Surface Preparation	Ultra-Low Roughness Polishing (Ra < 1 nm)	Minimizes optical scattering and maximizes photon collection efficiency, directly improving the signal-to-noise ratio (SNR) of the ODMR readout.
Integrated MW Structures	Custom Metalization Services (Ti/Pt/Au, Cu, W)	We offer in-house metal deposition, enabling the direct fabrication of on-chip microwave antennas or transmission lines onto the diamond surface, significantly enhancing the B₁ field homogeneity and strength for faster Rabi oscillations.
Logistics & Support	Global DDU/DDP Shipping & PhD Engineering Team	Our in-house PhD team provides expert consultation on material selection (e.g., optimizing nitrogen concentration vs. coherence time) and crystal orientation for specific quantum spin control projects.

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

View Original Abstract

The room temperature compatibility of the negatively charged nitrogen-vacancy (NV−) center in diamond makes it the ideal quantum system for a university teaching lab. Here, we describe a low-cost experimental setup for coherent control experiments on the electronic spin state of the NV− center. We implement spin-relaxation measurements, optically detected magnetic resonance, Rabi oscillations, and dynamical decoupling sequences on an ensemble of NV− centers. The relatively short times required to perform each of these experiments (&lt;10 min) demonstrate the feasibility of the setup in a teaching lab. Learning outcomes include basic understanding of quantum spin systems, magnetic resonance, the rotating frame, Bloch spheres, and pulse sequence development.

Tech Support

Original Source

DOI: https://doi.org/10.1119/10.0001905

References

2003 - Quantum technology: The second quantum revolution [Crossref]
2013 - The nitrogen-vacancy colour centre in diamond [Crossref]
2018 - Little bits of diamond: Optically detected magnetic resonance of nitrogen-vacancy centers [Crossref]
2019 - Quantum diamond spectrometer for nanoscale NMR and ESR spectroscopy [Crossref]
2019 - Quantum computing circuits and devices [Crossref]
2018 - Silicon qubits [Crossref]
2018 - Qubits based on semiconductor quantum dots [Crossref]
2005 - NMR techniques for quantum control and computation [Crossref]
2008 - Superconducting quantum bits [Crossref]