ABSTRACT To unfold their ultimate performance, a large number of photonics‐based quantum technologies require reliable emitters of single photons. Emission intensity fluctuations in these single‐photon emitters occur over a broad range of timescales from nanoseconds to more than several milliseconds, depending on the emitter, posing significant challenges for their future applicability. This paper focuses on quantum emitters with intensity fluctuations that occur at a rate comparable to the detection rate of the emitted light. In this regime, there is approximately one photon per bright period. Our method enables the determination of the bright‐state intensity, which is otherwise unobservable through a direct time‐domain measurement. This method is validated through simulations in various scenarios, and an analytical model is derived. We apply the method to measurements of both quantum emitters in hexagonal boron nitride and of centers in diamond. The gain in information about the states contributing to the emission dynamics enhances the understanding of bunching phenomena and, in particular, clarifies the influence of potential background light. This is crucial for identifying, designing, and fabricating bright single‐photon emitters for applications in quantum technologies.
ABSTRACT To unfold their ultimate performance, a large number of photonics‐based quantum technologies require reliable emitters of single photons. Emission intensity fluctuations in these single‐photon emitters occur over a broad range of timescales from nanoseconds to more than several milliseconds, depending on the emitter, posing significant challenges for their future applicability. This paper focuses on quantum emitters with intensity fluctuations that occur at a rate comparable to the detection rate of the emitted light. In this regime, there is approximately one photon per bright period. Our method enables the determination of the bright‐state intensity, which is otherwise unobservable through a direct time‐domain measurement. This method is validated through simulations in various scenarios, and an analytical model is derived. We apply the method to measurements of both quantum emitters in hexagonal boron nitride and of centers in diamond. The gain in information about the states contributing to the emission dynamics enhances the understanding of bunching phenomena and, in particular, clarifies the influence of potential background light. This is crucial for identifying, designing, and fabricating bright single‐photon emitters for applications in quantum technologies.
Abstract Single quantum light emitters are valuable resources for engineered quantum systems. They can function as robust single-photon generators, allow optical control of single spins, provide readout capabilities for atomic-scale sensors, and provide interfaces between stationary and flying qubits. Environmental factors can lead to single emitters exhibiting ‘blinking’, whereby the fluorescence level switches between on and off states. Detailed characterisation of this blinking behaviour including determining the switching rates is often a powerful way to gain understanding about the underlying physical mechanisms. While simple thresholds can be used to identify the on and off intervals and thus extract the rates from the time-series of counts for bright emitters with low background noise, such approaches become difficult for emitters fluorescing at low levels, high noise, or switching at fast rates. We develop a Bayesian approach capable of inferring switching rates directly from the time-series. This is able to deal with high levels of noise and fast switching in fluorescence traces. Moreover, the Bayesian inference also yields a robust picture of the parameter uncertainties, providing a benefit also for bright emitters in low-noise settings. The technique can be adapted to identify the underlying states as well as extracting the rates of switching. Finally, our method is applicable to a broad range of systems that show behaviour analogous to a blinking emitter.
Abstract Optical “blinking” normally refers to a switching behavior of fluorescence for quantum emissions between “ON” and “OFF” state. For quantum dots, single molecules, and nitrogen‐vacancy centers in diamond, it usually stems from conversions between two different charge states, with one emitting strong and bright fluorescence while the other scattering weak or no fluorescence. Here, a different type of blinking from single emitters in ion implanted diamond is reported, with both blinking states exhibiting detectable photoluminescence under nonresonant excitation. Thanks to the low jumping rates, the dynamics of the emission can be directly monitored. The quadratic power dependence of the conversion rates suggests the possibility of two‐photon ionization process in quantum jumps. This work provides extra insights into the photodynamics of the spectral jumps on defect‐based single‐photon emitters hosted in wide‐bandgap semiconductors.
Quantum communication and quantum metrology established a demand for an accessible solid state systems which can generate a stream of single photons on demand [1]. Although single photon emission has been demonstrated from quantum dots (QD)[1,2], single molecules [3] and nanowires [4], their practical operation is limited by the temperature or photostability. Diamond crystals, however, are the most promising platform for generation of robust, photo-stable, single photons at room temperature [5,6]. Nevertheless, out of more than 500 existing optical centers in diamond only three known centers demonstrated a clear single photon emission: the nitrogen-vacancy complex [6,7], the silicon-vacancy complex [8] and the nickel-nitrogen complex [9,10]. Recent progress in materials science and fabrication techniques of diamond color centers unveiled novel quantum emitters with photo-physical properties surpassing the current mainstream [11,12,13]. Consequently, the versatility of the diamond lattice to host various impurities which give luminescence signals lead to a dramatic discovery of ultra bright single photon emitters operating in the MHz regime [14]. These new centers, comparable with QD in terms of brightness [1], but have the tremendous advantage of their room temperature operation and photo-stability. Furthermore, it opened a new avenue to investigate essentially an unknown group of single photon emitters. A brief description of the fabrication methods and a detailed quantum optical characterization of this class of diamond emitters is the subject of this presentation. In particular we will present the photo-physical properties of a novel family of single photon emitters, most likely originated from Cr impurities within the chemical vapor deposition grown nano-diamond crystals. We concentrate on the typical emission lines in the range of 740 - 790 nm, which exhibit single photon emission with count rate in the range of 0.8-3.2 106 counts/s at the limit of infinite optical excitation power, and life time as short as 1 ns. Even more, some of the emitters exhibit a photon statistics without any photon bunching, indicating a two-level system with unitary quantum efficiency. We will also show preliminary results of a resonant excitation at 4 K. We will highlight future directions to optimize these sources and avenues to investigate the fundamental properties of these centers.
Sources of single photons are integral to a number of applications in the emerging field of quantum technologies. For any practical implementation of single-photon sources, a variety of different properties and an overall comprehensive characterization of the sources are required. Color centers in hBN and group IV color centers in diamond are promising candidate sources due to their favorable properties and rich internal level structure. Both of these candidates, however, also present some serious challenges. Although bright and spectrally narrow, defects in hBN suffer from emission instabilities. Furthermore, limited knowledge about their atomic composition leads to behaviour, which is often unpredictable. Meanwhile, Group IV centers generally exhibit low extraction efficiencies due to total internal reflection inside the high-index diamond host material. In this thesis, several large-scale series of experiments are conducted to investigate both types of emitters in a confocal fluorescence microscope at room temperature. The excitation characteristics of a large number of single-photon emitters in hBN from a narrow spectral window are investigated using a fully automated procedure. The results are compared to theoretical predictions for several carbon defects from the literature to gain further knowledge of the atomic nature of the underlying defects. Based on this approach, the CB, CN, CBVN, and CNVB centers are confidently ruled out as possible origins of the observed emission. Some uncertainty remains about the assignment of the carbon trimer C2CN as well as carbon-based donor-acceptor pairs. In a separate series of experiments, emission instabilities of hBN emitters from the same spectral region are studied. The detected fluctuations in brightness were conclusively attributed to spectral diffusion of the emission. Furthermore, optical stabilization of these effects via short-wavelength irradiation favors an explanation of the observed behavior via nearby charge carriers and the resulting Stark effect. Tin-vacancies, as representatives of group IV centers, are studied in a novel type of diamond waveguide structure for light collection enhancement. A center with sharp zero-phonon emission around 619 nm, a g(2)(0) value of 0.32, and simultaneous stable count rate of 3.4 Mcps was found. By restricting the collection to the zero-phonon line, g(2)(0) = 0.1 could be achieved. In a widespread characterization of the sample, it was found that most structures contain more than one negatively charged SnV center, which leaves an opportunity to improve the implantation parameters. In additional experiments on single tin-vacancy centers, a possible transition to a higher excited state as well as the charge-state transitions of the defects were probed. The results of these measurements contribute to the growing body of research on tin-vacancies and other group IV centers.
Optical quantum technology needs efficient sources for non-classical light. Solid-state emitters provide excellent mode purity, high brightness, and often also stable operation up to room temperature. At the same time the spin of individual impurities can be entangled with emitted photons. Nano-photonic structures can dramatically enhance the photon emission efficiency and thus the yield of quantum information processing tasks involving photons. One example is a node of a quantum repeater network. In this presentation we address the issue of enhanced photon collection from optically active defects in the solid-state such as diamond [1] or two-dimensional material [2]. We briefly introduce the emitters and then describe recent experiments where we couple them to dielectric/plasmonic antennas [3] and to SiO2/Si light collecting structures [4]. References [1] “Fiber-Coupled Diamond Micro-Waveguides toward an Efficient Quantum Interface for Spin Defect Centers”, M. Fujiwara, O. Neitzke, T. Schröder, A. W. Schell, J. Wolters, J. Zheng, S. Mouradian, M. Almoktar, S. Takeuchi, D. Englund, and O. Benson, ACS Omega 2, 7194-7202 (2017) [2] “Photodynamics of quantum emitters in hexagonal boron nitride revealed by low-temperature spectroscopy“, B. Sontheimer, M. Braun, N. Nikolay, N. Sadzak, I. Aharonovich, and Oliver Benson, Phys. Rev B 96, 121202(R) (2017). [3] “Accurate placement of single nano particles on opaque conductive structures“, N. Nikolay, N. Sadzak, A. Dohms, B. Lubotzky, H. Abudayyeh, R. Rapaport, and O. Benson, Appl. Phys. Lett, accepted (2018); arXiv:1807.10605 [4] “Fine-tuning of whispering gallery modes in on-chip silica microdisk resonators within a full spectral range“, R. Henze, C. Pyrlik, A. Thies, J.M. Ward, A. Wicht, O. Benson, Appl. Phys. Lett. 102, 041104 (2013).
The exploitation of emerging quantum technologies requires efficient fabrication of key building blocks. Sources of single photons are extremely important across many applications as they can serve as vectors for quantum information—thereby allowing long-range (perhaps even global-scale) quantum states to be made and manipulated for tasks such as quantum communication or distributed quantum computation. At the single-emitter level, quantum sources also afford new possibilities in terms of nanoscopy and bio-marking. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, as they are a photostable solid-state source of single photons at room temperature. In this review, we discuss the state of the art of diamond-based single-photon emitters and highlight their fabrication methodologies. We present the experimental techniques used to characterize the quantum emitters and discuss their photophysical properties. We outline a number of applications including quantum key distribution, bio-marking and sub-diffraction imaging, where diamond-based single emitters are playing a crucial role. We conclude with a discussion of the main challenges and perspectives for employing diamond emitters in quantum information processing.