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Time-dependent Mandel Q parameter analysis for a hexagonal boron nitride single photon source

Callum Jones, Jolly Xavier, Samir Vartabi Kashanian, Minh Nguyen, Igor Aharonovich, Frank Vollmer

Published Feb 27, 2023• 14 citations
Publisher

Abstract

The time-dependent Mandel Q parameter, Q ( T ), provides a measure of photon number variance for a light source as a function of integration time. Here, we use Q ( T ) to characterise single photon emission from a quantum emitter in hexagonal boron nitride (hBN). Under pulsed excitation a negative Q parameter was measured, indicating photon antibunching at an integration time of 100 ns. For larger integration times Q is positive and the photon statistics become super-Poissonian, and we show by comparison with a Monte Carlo simulation for a three-level emitter that this is consistent with the effect of a metastable shelving state. Looking towards technological applications for hBN single photon sources, we propose that Q ( T ) provides valuable information on the intensity stability of single photon emission. This is useful in addition to the commonly used g (2) ( τ ) function for the complete characterisation of a hBN emitter.

DOI
10.1364/oe.485216

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The time-dependent Mandel Q parameter, Q(T), provides a measure of photon number variance for a light source as a function of integration time. Here, we use Q(T) to characterise single photon emission from a quantum emitter in hexagonal boron nitride (hBN). Under pulsed excitation a negative Q parameter was measured, indicating photon antibunching at an integration time of 100 ns. For larger integration times Q is positive and the photon statistics become super-Poissonian, and we show by comparison with a Monte Carlo simulation for a three-level emitter that this is consistent with the effect of a metastable shelving state. Looking towards technological applications for hBN single photon sources, we propose that Q(T) provides valuable information on the intensity stability of single photon emission. This is useful in addition to the commonly used $g^{(2)}(τ)$ function for the complete characterisation of a hBN emitter.

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The time-dependent Mandel Q parameter, Q ( T ), provides a measure of photon number variance for a light source as a function of integration time. Here, we use Q ( T ) to characterise single photon emission from a quantum emitter in hexagonal boron nitride (hBN). Under pulsed excitation a negative Q parameter was measured, indicating photon antibunching at an integration time of 100 ns. For larger integration times Q is positive and the photon statistics become super-Poissonian, and we show by comparison with a Monte Carlo simulation for a three-level emitter that this is consistent with the effect of a metastable shelving state. Looking towards technological applications for hBN single photon sources, we propose that Q ( T ) provides valuable information on the intensity stability of single photon emission. This is useful in addition to the commonly used g (2) ( τ ) function for the complete characterisation of a hBN emitter.
The time-dependent Mandel Q parameter, Q(T), provides a measure of photon number variance for a light source as a function of integration time. Here, we use Q(T) to characterise single photon emission from a quantum emitter in hexagonal boron nitride (hBN). Under pulsed excitation a negative Q parameter was measured, indicating photon antibunching at an integration time of 100 ns. For larger integration times Q is positive and the photon statistics become super-Poissonian, and we show by comparison with a Monte Carlo simulation for a three-level emitter that this is consistent with the effect of a metastable shelving state. Looking towards technological applications for hBN single photon sources, we propose that Q(T) provides valuable information on the intensity stability of single photon emission. This is useful in addition to the commonly used g(2)(τ)g^{(2)}(τ)g(2)(τ) function for the complete characterisation of a hBN emitter.
We report on the quantum photon statistics of hexagonal boron nitride (h-BN) quantum emitters by analyzing the Mandel Q parameter. We have measured the Mandel Q parameter for h-BN quantum emitters under various temperature and pump power excitation conditions. Under pulsed excitation, we can achieve a Mandel Q of −0.002, and under continuous-wave excitation, this parameter can reach −0.0025. We investigate the effect of cryogenic temperatures on Mandel Q and conclude that the photon statistics vary weakly with temperature. Through the calculation of spontaneous emission from an excited two-level emitter model, we demonstrate good agreement between the measured and calculated Mandel Q parameters when accounting for the experimental photon collection efficiency. Finally, we illustrate the usefulness of Mandel Q in quantum applications by the example of random number generation and analyze the effect of Mandel Q on the speed of generating random bits via this method.
Single photon sources based on single emitters such as 2D materials and impurities in diamond are of great interest for many application fields including quantum communication, quantum metrology and quantum sensing. In photometry and radiometry, a single photon source, having the ability to emit only one photon in a well-defined time and frequency domain, represents a promising candidate to realize a photon number-based primary standard for quantum radiometry. At the Korea Research Institute of Standards and Science (KRISS), we have realized three kinds of single photon sources based on various single emitters at room temperature: silicon vacancy in diamond, defects in gallium nitride (GaN), and vacancy in hexagonal boron nitride (hBN). We found common factors related with the relaxation times of the internal states that indirectly affect the photon number stability. We observed a high photon number stability in the GaN emitter due to faster relaxation times compared with the hBN emitter, which on the other hand produced high rates of photons per second (> 106). Moreover, 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.
This thesis decay rate enhancement and photophysics of nitrogen vacancy (NV) centers in diamond and quantum emitters in hexagonal boron nitride (hBN). The NV center in diamond is a unique physical system that finds use in many quantum technologies such as quantum sensing, quantum information processing and single photon generation. Consisting of a substitutional nitrogen atom next to a vacant lattice site, the NV center introduces discrete electronic energy levels within the wide bandgap of diamond. The NV center can be optically excited and will emit single photons upon relaxation that hold information of the spin state of the NV center. In this thesis, we use metallic structures to modify and enhance the decay rate of NV centers in bulk and nano diamonds in three different experiments. Such an enhancement is a way to improve the usability of NV as a single photon source. Using TiN films with metamaterial properties we observe a 2-fold decrease of the total excited state lifetime of NV centers in nano diamonds, when comparing to similar NV centers not influenced by the TiN films. For shallow implanted NV centers in bulk diamond we experimentally investigate how a decay rate enhancement influences the signal-to-noise ratio (SNR) in spin readout measurements. In this experiment we perform spin state readout before and after introducing a rate enhancement and find a 30 % drop in spin contrast. We model the spin readout measurements using a five-level model and use that to predict the SNR under higher rate enhancement. In the last NV related experiment we use a curved metallic mirror on top of shallow implanted NV centers, to measure the continuous lifetime modification as a function of distances to the mirror. This allows us to determine the internal quantum efficiency (IQE) by fitting the experimental data with a model that includes calculating the expected Purcell factor. We find IQE values of 0.70±0.07 and 0.82±0.08 for implantation depths of 4.5±1 and 8±2 nm, respectively. Last but not least, newly discovered bright single photon emitters in two dimensional hBN were investigated. Similar to the NV center they are believed to be crystal defects, but the defect configuration is not fully known. In this thesis, the photophysics of quantum emitters in hBN nano flakes are investigated. Intensity autocorrelation measurements indicate the presence of at least two metastable states, seen by distinct photon bunching levels on long time scales in the g(2)(τ)-functions. We also observe blinking behaviour, which we show can be explained by changes in the IQE. From rate equation fitting we find that transition rates scale linearly with excitation power. Based on the transition rates we estimate the IQE to be close to unity for excitation powers below saturation.
High-purity quantum emitters in hexagonal boron nitride (hBN) hold the potential for use as high-quality quantum random number generators (QRNGs). In this work, we verify a QRNG using a deterministically placed quantum emitter in nanoindented hBN with∼95%\mathbf{\sim 9 5 \%}∼95%single-photon purity.