Near-infrared-assisted charge control and spin readout of the nitrogen-vacancy center in diamond

At a Glance

Metadata	Details
Publication Date	2016-12-09
Journal	Physical review. B./Physical review. B
Authors	David A. Hopper, Richard R. Grote, Annemarie L. Exarhos, Lee C. Bassett
Institutions	University of Pennsylvania
Citations	71
Analysis	Full AI Review Included

Technical Documentation & Analysis: Near-Infrared-Assisted Charge Control and Spin Readout of the Nitrogen-Vacancy Center in Diamond

This document analyzes the research detailing enhanced NV center charge control and spin readout using multicolor illumination, focusing on the material requirements and how 6CCVD’s advanced MPCVD diamond solutions can support and extend this critical quantum research.

Executive Summary

The research demonstrates significant advancements in Nitrogen-Vacancy (NV) center initialization and spin readout fidelity by leveraging nonlinear multiphoton absorption mechanisms in diamond.

Record Initialization Purity: Achieved the highest-purity all-optical NV$^-$ initialization reported to date, reaching 91.0% ± 0.6% steady-state population using coincident 532 nm and Near-Infrared (NIR) illumination.
Enhanced Spin Readout: Developed a Spin-to-Charge Conversion (SCC) protocol via selective singlet ionization, resulting in a 6-fold improvement in the single-shot Signal-to-Noise Ratio (SNR = 0.32) over traditional photoluminescence (PL) readout.
Speedup Potential: The optimized multi-SCC protocol is predicted to yield up to a 15-fold SNR boost (SNR=0.85) and offers an orders-of-magnitude experimental speedup for operation times exceeding 30 µs.
Advanced Device Integration: The experiment utilized a Solid Immersion Lens (SIL) fabricated directly onto the diamond surface via Focused Ion Beam (FIB) milling, increasing photon collection efficiency by a factor of 6 and excitation efficiency by a factor of 10.
Material Requirement: Success relies on high-quality, low-defect single crystal diamond (SCD) to maintain long spin coherence times (T₂) necessary for quantum applications.
Application Relevance: These all-optical techniques are universally applicable to both single-NV and ensemble experiments, driving advances in room-temperature magnetometry and quantum information science.

Technical Specifications

The following hard data points were extracted from the research paper, highlighting the performance metrics achieved:

Parameter	Value	Unit	Context
NV$^-$ Initialization Purity (Max)	91.0 ± 0.6	%	All-optical, 532 nm + NIR
Single-Shot SNR (Measured)	0.32	N/A	Multi-SCC protocol, 6-fold gain over PL
Single-Shot SNR (Predicted Ideal)	0.85	N/A	Assuming 100% singlet ionization
SNR Improvement (Measured)	6	Fold	Over traditional PL readout
Spin Readout Noise (Measured)	4.6	x SQL	Standard Quantum Limit (SQL)
Excitation Wavelengths	532, 592, 900-1000	nm	Visible CW and NIR picosecond pulses
NIR Pulse Repetition Rate	40	MHz	Supercontinuum source
Charge Readout Fidelity (F_c)	99.1 ± 0.4	%	Single-shot, 592 nm excitation
Non-Destructivity (F_D)	> 96	%	Low illumination power (75 nW, 15 ms)
SIL Collection Efficiency Boost	6	Factor	Compared to standard objective
Metastable Singlet Lifetime (T_Fit)	182 ± 10	ns	Measured via NIR delay

Key Methodologies

The experimental success hinges on precise control over material properties, optical gating, and device fabrication:

Excitation Sources and Gating: Continuous-wave (CW) 532 nm (green) and 592 nm (yellow) lasers were used, temporally gated via Acousto-Optic Modulators (AOMs). The 532 nm AOM was configured in a double-pass setup to achieve >60 dB extinction, crucial for preventing charge state cycling during high-fidelity readouts.
NIR Source: A single-shot, picosecond-pulsed supercontinuum source, band-pass filtered to 900-1000 nm, provided the NIR illumination at a 40 MHz repetition rate.
Confocal Microscopy: A home-built scanning confocal microscope was used to address individual NV centers, co-aligning the three excitation sources (532 nm, 592 nm, NIR).
High-Fidelity Charge Readout: Non-destructive charge state determination was performed using 592 nm light (75-300 nW) tuned to exploit the blue-shifted absorption spectrum of NV$^-$ compared to NV$^0$.
Solid Immersion Lens (SIL) Fabrication: A 6 µm diameter SIL was fabricated around pre-selected NV centers directly on the diamond surface using Focused Ion Beam (FIB) milling, preceded by PMMA masking and an AuPd discharge layer.
Spin Control: Microwave (MW) pulses (~2.87 GHz) were delivered via a 20 µm diameter gold wire placed across the diamond surface to control the NV ground-state spin sublevels (m_s = 0, ±1).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity diamond materials and advanced fabrication services required to replicate, optimize, and scale this groundbreaking quantum research.

Applicable Materials

The high-fidelity spin readout and long coherence times (T₂) demonstrated require diamond with extremely low concentrations of parasitic defects (like substitutional nitrogen, P1 centers).

Research Requirement	6CCVD Solution	Material Specification	Core Value Proposition
High Spin Coherence (T₂)	Electronic Grade Single Crystal Diamond (SCD)	Nitrogen concentration < 1 ppb. High purity, low strain.	Ensures maximum T₂ time, critical for qubit performance and high-sensitivity magnetometry.
Charge Stability/Control	Optical Grade SCD	Excellent surface quality (Ra < 1 nm) and high transmission in visible/NIR bands.	Minimizes scattering losses and supports the complex multicolor multiphoton absorption protocols (532 nm, 592 nm, 900-1000 nm).
Ensemble Applications	High-Purity Polycrystalline Diamond (PCD)	Plates up to 125 mm diameter, thickness up to 500 µm.	Ideal for scaling up magnetometry or sensing applications where large area coverage is required.

Customization Potential

The paper highlights the necessity of integrating micro-structures (SILs) and metallic components (gold wires) directly onto the diamond substrate. 6CCVD offers comprehensive in-house services to meet these advanced engineering needs:

Custom Substrate Dimensions: 6CCVD provides SCD and PCD plates/wafers up to 125 mm in diameter. We offer custom diamond substrates up to 10 mm thick, providing the necessary bulk material for deep, high-efficiency Solid Immersion Lens (SIL) fabrication via FIB or etching.
Precision Metalization: The experiment used a 20 µm gold wire for microwave delivery. 6CCVD offers custom thin-film metalization stacks (including Au, Pt, Ti, Pd, W, Cu) deposited directly onto the diamond surface, enabling integrated microwave strip lines, electrodes for electrical gating (as mentioned in related work [21]), and ohmic contacts.
Ultra-Low Roughness Polishing: Achieving high-fidelity optical coupling, especially for SILs, demands exceptional surface quality. 6CCVD guarantees Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal optical scattering losses.

Engineering Support

The complex charge dynamics observed (non-monotonic variations, competing multiphoton absorption) require deep material science expertise.

Material Selection Consultation: 6CCVD’s in-house PhD team specializes in MPCVD diamond growth and defect engineering. We can assist researchers in selecting the optimal material grade and NV creation method (e.g., implantation vs. in-situ growth) to achieve the desired NV density and spin coherence time (T₂) for similar quantum sensing and qubit projects.
Global Logistics: We offer reliable global shipping (DDU default, DDP available) to ensure rapid delivery of custom-engineered diamond solutions worldwide, minimizing project delays.

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

View Original Abstract

We utilize nonlinear absorption to design all-optical protocols that improve\nboth charge state initialization and spin readout for the nitrogen-vacancy (NV)\ncenter in diamond. Non-monotonic variations in the equilibrium charge state as\na function of visible and near-infrared (NIR) optical power are attributed to\ncompeting multiphoton absorption processes. In certain regimes, multicolor\nillumination enhances the steady-state population of the NV’s negative charge\nstate above 90%. At higher NIR intensities, selective ionization of the singlet\nmanifold facilitates a protocol for spin-to-charge conversion that dramatically\nenhances the spin readout fidelity. We demonstrate a 6-fold increase in the\nsignal-to-noise ratio for single-shot spin measurements and predict an\norders-of-magnitude experimental speedup over traditional methods for emerging\napplications in magnetometry and quantum information science using NV spins.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.94.241201