Emitters of single photons are essential resources for emerging quantum technologies and developed within different platforms including nonlinear optics and atomic and solid-state systems. The energy-level structures of emission processes are critical for reaching and controlling high-quality sources. The most commonly applied test uses a Hanbury Brown and Twiss (HBT) setup to determine the emitter energy-level structure based on fitting temporal correlations of photon detection events. However, only partial information about the emission process is extracted from such detection, that might be followed by an inconclusive fitting of the data. This process predetermines our limited ability to quantify and understand the dynamics in the photon emission process that are of importance for the applications in communication, sensing, and computing. In this work, we present a complete analysis based on all normalized coincidences between detection and no-detection events recorded in the same HBT setup to certify expected properties of an emitted photonic state. As a proof of concept we apply our methodology to single nitrogen-vacancy centers in diamond, in which case the certification conclusively rejects a model based on a two-level emitter that radiates a photonic state mixed with any classical noise background. Published by the American Physical Society 2024
Emitters of single photons are essential resources for emerging quantum technologies and developed within different platforms including nonlinear optics and atomic and solid-state systems. The energy-level structures of emission processes are critical for reaching and controlling high-quality sources. The most commonly applied test uses a Hanbury Brown and Twiss (HBT) setup to determine the emitter energy-level structure based on fitting temporal correlations of photon detection events. However, only partial information about the emission process is extracted from such detection, that might be followed by an inconclusive fitting of the data. This process predetermines our limited ability to quantify and understand the dynamics in the photon emission process that are of importance for the applications in communication, sensing, and computing. In this work, we present a complete analysis based on all normalized coincidences between detection and no-detection events recorded in the same HBT setup to certify expected properties of an emitted photonic state. As a proof of concept we apply our methodology to single nitrogen-vacancy centers in diamond, in which case the certification conclusively rejects a model based on a two-level emitter that radiates a photonic state mixed with any classical noise background. Published by the American Physical Society 2024
Quantum opticians usually employ and exploit genuine or modified HBT setups as standard tools for characterizing non-classical states of light. One the one hand, HBT measurements permit to characterize the emission statistics of photonic modes that are, depending on the emitter and on the spatial and spectral features, thermal, poissonnian, sub-poissonnian, or deterministic. On the other hand, auto-correlation and cross-correlation functions, recorded in the single photon counting regime, permit to infer the unique properties of single photon and two photons sources, that are further utilized in quantum communication applications. For instance, when applied to a single photon source, a genuine HBT setup helps qualifying the uniqueness emission feature. Moreover, when applied to a two photon source, a modified HBT setup permits measuring simultaneous emission time correlations, as well as single photon coherence time. During this talk, I will review some situations in which HBT type setups and related measurements are exploited in and for quantum optics or communication experiments.
The rapid growth of quantum technologies has driven the development of quantum defects for both single photon sources as well as for spin qubit and sensor applications. These artificial atoms in wide bandgap solid-state materials such as diamond and hBN offer the possibility of a truly quantum deterministic source. These single photon emitting quantum defects exhibit antibunching that can be quantified by performing the Hanbury-Brown Twiss (HBT) experiment. The HBT experiment allows one to evaluate the second-order autocorrelation (g(2)(τ )) function, which is a central measure in determining the quality of single photon emission. To enhance the various emission parameters such as intensity, wavelength, and directionality from these defects the development of photonic structures become essential. Here, we study single photon emission from a diamond nanopillar array containing Nitrogen Vacancy (NV) centers. We spatially map the g(2)(τ ) function and radiative lifetimes in these samples and correlate the two quantities. Crucially, we observe that the measured antibunching varies as a function of position of the objective relative to the nanopillar, even across the same pillar. This likely shows the dependence of the apparent antibunching to the angle of excitation and detection in such photonic structures. Our results highlight the importance of structural and geometric factors in g(2)(τ ) measurements of emitters, especially when embedded in photonic structures. These should be carefully understood in evaluating the quality of the single photon sources.
Photon emission correlation spectroscopy (PECS) is an indispensable tool for the study of atoms, molecules, and, more recently, solid-state quantum defects. In solid-state systems, its most common use is as an indicator of single-photon emission, a key property for quantum technology. Beyond single-photon purity, photon correlation measurements can provide a wealth of information that can reveal details about an emitter's electronic structure and optical dynamics that are hidden by other spectroscopy techniques. This thesis explores the application of PECS to study and understand the optical dynamics of quantum emitters. The first part of this thesis presents a guide to a standardized framework for using PECS to facilitate materials exploration for qubit candidates. This includes discussion of theoretical background, considerations for data acquisition and statistical analysis, and interpretation of PECS. It also illustrates how this experimental technique can be paired with optical dynamics simulations to formulate an electronic model for unknown quantum emitters. The second part of this thesis implements the practices discussed in the first part to explore the optical dynamics of two systems: the nitrogen-vacancy (NV) center in diamond and a quantum emitter in hexagonal boron nitride (h-BN). The NV center is a promising platform for applications in quantum sensing, quantum communication, and quantum networks. In particular, its spin and charge dynamics constitute useful attributes that can be harnessed for quantum control protocols. This thesis models and quantifies the transition rates that govern spin and charge dynamics in the NV center, utilizing PECS measurements, analysis, and simulations as a function of magnetic field, and excitation power. These findings can further inform the design of quantum control protocols. H-BN hosts pure single-photon emitters that have shown evidence of optically detected electronic spin dynamics. However, the electrical and chemical structure of these optically addressable spins is unknown, and the nature of their spin-optical interactions remains mysterious. This thesis discusses time-domain optical and microwave experiments to characterize a single emitter in h-BN exhibiting room temperature optically detected magnetic resonance. It further discusses use of dynamical simulations to constrain and quantify transition rates in the model, and design of optical control protocols that optimize the signal-to-noise ratio for spin readout. This constitutes a necessary step towards quantum control of spin states in h-BN.
Photon emission correlation spectroscopy is an indispensable tool for the study of atoms, molecules, and, more recently, solid-state quantum defects. In solid-state systems, its most common use is as an indicator of single-photon emission, a key property for quantum technology. Beyond an emitter's single-photon purity, however, photon correlation measurements can provide a wealth of information that can reveal details about its electronic structure and optical dynamics that are hidden by other spectroscopy techniques. This tutorial presents a standardized framework for using photon emission correlation spectroscopy to study quantum emitters, including discussion of theoretical background, considerations for data acquisition and statistical analysis, and interpretation. We highlight important nuances and best practices regarding the commonly-used g(2)(tau=0)<0.5 test for single-photon emission. Finally, we illustrate how this experimental technique can be paired with optical dynamics simulations to formulate an electronic model for unknown quantum emitters, enabling the design of quantum control protocols and assessment of their suitability for quantum information science applications.
Photon-emission-correlation spectroscopy is an indispensable tool for the study of atoms, molecules, and, more recently, solid-state quantum defects.In solid-state systems, its most common use is as an indicator of single-photon emission, a key property for quantum technology.Beyond the single-photon purity of an emitter, however, photon-correlation measurements can provide a wealth of information that can reveal details about its electronic structure and optical dynamics that are hidden by other spectroscopy techniques.This tutorial presents a standardized framework for using photon-emission-correlation spectroscopy to study quantum emitters, including discussion of theoretical background, considerations for data acquisition and statistical analysis, and interpretation.We highlight important nuances and best practices regarding the commonly used g (2) (τ = 0) < 0.5 test for single-photon emission.Finally, we illustrate how this experimental technique can be paired with optical-dynamics simulations to formulate an electronic model for unknown quantum emitters, enabling the design of quantum control protocols and assessment of their suitability for quantum information science applications.
For applications in Quantum Information and Quantum Key Distribution an on-demand source of single photons is desirable because absolute security is of utmost importance. Photons are quantum systems; hence encoding information onto them offers a secure alternative to classical cryptography as a measurement cannot be performed on photons without altering their properties. The Nitrogen Vacancy (NV) centre in diamond is a good source of such photons. It is photo-stable and its location in diamond offers robustness. It has zero phonon line at 637 nm and its relative short luminescence life-time of about 12 ns makes it suitable for generating single photons. This thesis covers two aspects: Firstly the characterization of defects in diamonds and subsequent selection of diamonds suitable for use in the single photon setup and secondly, the development of the experimental setup for single photon generation. This thesis sets out to describe the development of a laboratory based single photon source using the NV centre in diamond. For this purpose a suite of diamond samples were selected and subjected to various spectroscopic tests in order to characterize and classify the samples, especially the presence of the NV centres and their concentrations. The characterization of the defects was done through the use of the following spectroscopic techniques: UltravioletVisible-Near infrared spectroscopy, Infrared spectroscopy, Electron Spin Resonance and Photoluminescence. These techniques enabled us to understand the types and origins of crystal defects that were present in the diamond samples used in this study and to use this to select diamonds that are most suitable for use in generation of single photons. The experimental setup for single photon generation using the NV centre is based on a confocal microscope arrangement. Single NV centres were identified by measuring the second order autocorrelation function of the fluorescence light emitted by the sample when illuminated with a laser. This measurement was done using a Hanbury-Brown Twiss (HBT) interferometer.