Toward the Realization of Single-Photon Sources for Radiometry Applications at Room Temperature

At a Glance

Metadata	Details
Publication Date	2023-01-01
Journal	IEEE Transactions on Instrumentation and Measurement
Authors	K.S. Hong, Hee‐Jin Lim, Dong-Hoon Lee, In‐Ho Bae, Kwang-Yong Jeong
Institutions	Korea Research Institute of Standards and Science, The University of Melbourne
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Single Photon Sources for Quantum Radiometry

Reference Paper: Lim et al., Characterization of single photon sources for radiometry applications at room temperature (arXiv:2007.10616v1)

Executive Summary

This research validates the performance of room-temperature single photon emitters (SPEs) in various wide band-gap materials—specifically Silicon Vacancy in Diamond (vc-SiV), defects in GaN, and vacancy in hBN—for establishing new quantum radiometry standards based on photon counting.

Core Achievement: Demonstrated repeatable radiant flux measurements over a wide range (femtowatts to picowatts) using SPEs as traceable light sources at room temperature.
Material Comparison: GaN defects exhibited the highest stability and repeatability (down to 30 ppm error), while hBN offered the highest photon count rates (> $10^6$ cps) but suffered from severe fluctuations due to slow blinking ($\tau_2 \approx 1.0$ µs).
Diamond Performance: vc-SiV in nano-diamonds showed low anti-bunching ($g^{<sup>2</sup>}(0) = 0.38 \pm 0.22$) and the fastest transition dynamics ($\tau_1$ near the instrumental time jitter limit).
Metrology Requirement: The study confirms that achieving high accuracy in few-photon metrology requires SPEs with both high count rates and high stability (low $\tau_2$).
Collection Challenge: Current collection efficiency is low (< 6.4%). The paper explicitly identifies the need for advanced photonics techniques, such as Solid Immersion Lenses (SILs), which necessitate high-quality, custom diamond substrates.
6CCVD Value Proposition: 6CCVD’s high-purity Single Crystal Diamond (SCD) and precision fabrication services are essential for overcoming collection efficiency limitations and enabling robust, scalable quantum radiometry devices.

Technical Specifications

Hard data extracted from the characterization of single photon emitters (SPEs) across three material platforms.

Parameter	Value	Unit	Context
Operating Temperature	Room Temperature	°C	All SPE characterizations
SiV $g^{<sup>2</sup>}(0)$ (Zero-Time Correlation)	$0.38 \pm 0.22$	Dimensionless	vc-SiV in diamond
GaN $g^{<sup>2</sup>}(0)$	$0.24 \pm 0.14$	Dimensionless	df-GaN defects
hBN $g^{<sup>2</sup>}(0)$	$0.33 \pm 0.05$	Dimensionless	vc-hBN vacancy
Maximum Photon Count Rate (hBN)	> $1.0 \times 10^{6}$	cps	Highest rate observed; limited by blinking
Maximum Photon Count Rate (SiV)	< $2.0 \times 10^{5}$	cps	Limited by internal efficiency and collection
GaN Repeatability Error	30	ppm	Highest repeatability achieved (M=20 repetitions)
hBN Blinking Time ($\tau_2$)	$1.0 \pm 0.1$	µs	Slow non-radiative relaxation (causes high fluctuation)
GaN Blinking Time ($\tau_2$)	$53 \pm 5$	ns	Fast non-radiative relaxation (contributes to high stability)
SiV ZPL Position	$\approx 737$	nm	Zero-Phonon Line wavelength
Collection Efficiency (Measured)	< 6.4	%	Overall efficiency including setup loss (20%)
Radiant Flux Range Demonstrated	Tens of fW to 1 pW	W	Wide range for radiometry application

Key Methodologies

The experimental approach focused on synthesizing SPEs in wide band-gap materials and characterizing their photon statistics using a high-stability dual-detection system.

SiV Sample Synthesis: Silicon Vacancy centers were created in nano-diamonds (50-100 nm diameter) grown via a silicon-free CVD process on an Iridium substrate, followed by Silicon implantation to achieve high SiV purity.
hBN Sample Preparation: Commercial hBN nano-flakes were dispersed on oxidized silicon and subjected to high-temperature annealing (800 °C for 30 min in 1 Torr Argon gas) to activate vacancy centers.
Optical Measurement Setup: A confocal microscopy system was used to confine fluorescence signals, coupled with Single Mode Fibers (SMFs) to ensure high stability and repeatable measurements of spectra and photon statistics.
Dual Detection System: A custom radiometry module was constructed featuring two detection modes sharing the same optical path: a Silicon Single Photon Avalanche Detector (SPAD) for photon counting (C) and a high-sensitivity photodiode for radiant power measurement (S).
Photon Statistics Analysis: Photon coincidence correlation $g^{<sup>2</sup>}(\tau)$ was measured using a Hanbury Brown-Twiss (HBT) setup via the Time-Tag Correlation (TTC) method, allowing derivation of anti-bunching ($\tau_1$) and blinking ($\tau_2$) time constants.
Radiant Flux Conversion: Photon count rate (C) was converted to radiant flux (S) using the theoretical relation $S = (hc/\lambda) \times DE(C) \times C$, where $DE(C)$ is an effective function incorporating quantum efficiency and detection dead-time corrections.

6CCVD Solutions & Capabilities

The research highlights the critical need for high-purity host materials and advanced optical integration (like Solid Immersion Lenses) to maximize collection efficiency and achieve the low uncertainty required for few-photon metrology. 6CCVD is uniquely positioned to supply the necessary materials and fabrication services to advance this research.

Applicable Materials

To replicate and extend the high-stability SiV research, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD): Essential for creating high-purity SiV emitters with minimal background photoluminescence (PL). Our SCD is grown via MPCVD, offering superior crystalline quality necessary for precise defect engineering (implantation or in-situ doping).
Polycrystalline Diamond (PCD) Substrates: For large-area device integration or applications where thermal management is critical, our PCD wafers (up to 125 mm) provide excellent thermal conductivity and mechanical robustness.
Boron-Doped Diamond (BDD): For future studies requiring integrated electrical control or sensing, BDD films can be grown with precise doping levels.

Customization Potential

The paper notes that collection efficiency (< 6.4%) is the primary limitation, suggesting that advanced optics like Solid Immersion Lenses (SILs) are necessary. 6CCVD specializes in the material preparation required for these advanced structures.

Research Requirement	6CCVD Capability	Technical Advantage for Quantum Radiometry
High-Quality Substrates for SILs (Requires ultra-smooth surfaces for high NA optics)	Precision Polishing (SCD): Achievable surface roughness $R_a < 1$ nm.	Enables direct fabrication of hemispherical or Weierstrass SILs onto the SCD host, drastically increasing photon collection efficiency and enabling the use of sub-Poisson statistics.
Custom Dimensions & Thickness (Need for robust, integrated devices beyond nano-flakes)	Custom Dimensions: Plates/wafers up to 125 mm (PCD). Thickness Control: SCD (0.1 µm - 500 µm), Substrates (up to 10 mm).	Supports scalable manufacturing and integration of SPEs into standardized metrology equipment.
Integrated Electrical Contacts (Required for excitation control or device integration)	In-House Custom Metalization: Deposition of Au, Pt, Pd, Ti, W, and Cu.	Allows researchers to prototype integrated devices with electrical contacts or micro-heaters directly on the diamond surface, facilitating precise control over SPE excitation and stability.
Global Supply Chain (Need for reliable, fast delivery of specialized materials)	Global Shipping: DDU default, DDP available worldwide.	Ensures rapid access to high-specification diamond materials, accelerating research timelines regardless of location.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers can assist researchers in optimizing material selection and defect creation protocols for Single Photon Emitter (SPE) and Quantum Radiometry projects. We provide consultation on:

Selecting the optimal SCD grade (e.g., low-nitrogen vs. high-purity) for specific defect creation methods (implantation vs. in-situ growth).
Designing custom substrate geometries and polishing specifications necessary for high-efficiency optical coupling (e.g., SIL fabrication).
Developing metalization schemes for robust electrical or thermal interfaces.

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

View Original Abstract

A single photon source with high repeatability and low uncertainties is the key element for few-photon metrology based on photon numbers. While low photon number fluctuations and high repeatability are important figures for qualification as a standard light source, these characteristics are limited in single photon emitters by some malicious phenomena like blinking or internal relaxations to varying degrees in different materials. This study seeks to characterize photon number fluctuations and repeatability for radiometry applications at room temperature. For generality in this study, we collected photon statistics data with various single photon emitters of $g^{(2)}(0) < 1$ at low excitation power and room temperature in three material platforms: silicon vacancy in diamond, defects in GaN, and vacancy in hBN. We found common factors related with the relaxation times of the internal states that indirectly affect photon number stability. We observed a high stability of photon number with defects in GaN due to faster relaxations compared with vacancies in hBN, which on the other hand produced high rates ($> 10^6$) of photons per second. Finally, we demonstrate repeatable radiant flux measurements of a bright hBN single photon emitter for a wide radiant flux range from a few tens of femtowatts to one picowatt.

Tech Support

Original Source

DOI: https://doi.org/10.1109/tim.2023.3289550

References

2022 - Single photon sources for radiometry applications at room temperature