Abstract Since the onset of the 1990s, the development of single-molecule spectroscopy has led to the discovery of various quantum optical signatures in organic single molecules. The single-photon nature of an organic chromophore is of particular importance because of its potential as a nonclassical photon source at room temperature for quantum information science and optical quantum computing. This condensed review focuses on the introduction of fundamental knowledge and basic experimental methods for single-photon sources and organic molecular photophysics and summarizes the research developments in this field, providing an understanding of quantum emission from organic single molecules.
Abstract Since the onset of the 1990s, the development of single-molecule spectroscopy has led to the discovery of various quantum optical signatures in organic single molecules. The single-photon nature of an organic chromophore is of particular importance because of its potential as a nonclassical photon source at room temperature for quantum information science and optical quantum computing. This condensed review focuses on the introduction of fundamental knowledge and basic experimental methods for single-photon sources and organic molecular photophysics and summarizes the research developments in this field, providing an understanding of quantum emission from organic single molecules.
The development of single-photon sources has been nothing but rapid in recent years, with quantum emitter-based systems showing especially impressive progress. In this article, we give an overview of the developments in single-photon sources based on single molecules. We will introduce polycyclic hydrocarbons as the most commonly used emitter systems for the realization of an organic solid-state single-photon source. At cryogenic temperatures this special class of fluorescent molecules demonstrates remarkable optical properties such as negligible dephasing, indefinite photostability, and high photon rates, which make them attractive as fundamental building blocks in emerging quantum technologies. To better understand the general properties and limitations of these molecules, we discuss sample preparation and relevant emitter parameters such as absorption and emission spectra, lifetime, and dephasing. We will also give an overview of light extraction strategies as a crucial part of a single-photon source. Finally, we conclude with a look into the future, displaying current challenges and possible solutions.
The concept of the photon , central to Einstein's explanation of the photoelectric effect, is exactly 100 years old. Yet, while photons have been detected individually for more than 50 years, devices producing individual photons on demand have only appeared in the last few years. New concepts for single-photon sources, or 'photon guns', have originated from recent progress in the optical detection, characterization and manipulation of single quantum objects. Single emitters usually deliver photons one at a time. This so-called antibunching of emitted photons can arise from various mechanisms, but ensures that the probability of obtaining two or more photons at the same time remains negligible. We briefly recall basic concepts in quantum optics and discuss potential applications of single-photon states to optical processing of quantum information: cryptography, computing and communication. A photon gun's properties are significantly improved by coupling it to a resonant cavity mode, either in the Purcell or strong-coupling regimes. We briefly recall early production of single photons with atomic beams, and the operation principles of macroscopic parametric sources, which are used in an overwhelming majority of quantum-optical experiments. We then review the photophysical and spectroscopic properties and compare the advantages and weaknesses of various single nanometre-scale objects used as single-photon sources: atoms or ions in the gas phase and, in condensed matter, organic molecules, defect centres, semiconductor nanocrystals and heterostructures. As new generations of sources are developed, coupling to cavities and nano-fabrication techniques lead to improved characteristics, delivery rates and spectral ranges. Judging from the brisk pace of recent progress, we expect single photons to soon proceed from demonstrations to applications and to bring with them the first practical uses of quantum information.
Single organic molecules make excellent single photon sources, emitting photons with high efficiency and at favourable wavelengths for coupling to other quantum systems, including alkali atoms. I will discuss techniques to create organic crystals containing single photon emitting molecules, and our recent results applying strain to these crystals to tune their emission wavelength. I will show that subsequent photons emitted by a single molecule can undergo quantum interference at a beam splitter, a vital tool in optical quantum computing and communication, and will discuss how discuss how to assess photon indistinguishability using both continuous and pulsed lasers. While molecular excitation and radiative emission is efficient, generated photons can be difficult to collect without the use of photonic structures. I will discuss our recent efforts in coupling single molecules to waveguides and nanophotonic cavities.
Efficient quantum light sources and non-linear optical elements at the few photon level are the basic ingredients for most applications in nano and quantum technologies. On the other hand, a scalable platform for quantum ICT typically requires reliable light matter interfaces and on-chip integration. In this work we demonstrate the potential of a novel hybrid technology which combines single organic molecules as quantum emitters and dielectric chips [1]. Dibenzoterrylene molecules in anthracene crystals (DBT:Ac) are particularly suitable quantum systems for this task, since they exhibit long-term photostability in thin samples [2], easy fabrication methods and life-time limited emission at cryogenic temperatures [3]. We demonstrate at room temperature the emission of single photons from DBT molecules into ridge waveguides with a branching ratio up to 40%. The overall single-photon source efficiency, including emission into the guided mode, propagation losses, and emission into a quasi-gaussian mode in free space, is estimated around 16%. These results are competitive with state-of-the-art single photon emission into propagating guided modes from solid state systems [4], while offering a novel platform with unprecedented versatility. References [1] P. Lombardi et al., Arxiv: 1701.00459v1 (2017). [2] C. Toninelli et al., Opt. Express 18, 6577 (2010). [3] A. A. L. Nicolet et al., ChemPhysChem 8, 1929 (2007). [4] I. Zadeh et al., Nano Lett. 16, 2289 (2016); R. S. Daveau et al., Arxiv: 1610.08670v1 (2016). [5] J. Hwang et. al., New J. Phys. 13, 085009 (2011); H.-W. Lee et al., Phys. Rev. A 63, 012305 (2000).
A single-photon source is an essential tool for the emerging field of quantum technologies. Ideally, it should be spectrally compatible with other photonic devices while providing a high flux of narrow-band photons. The single organic dye molecule dibenzanthanthrene under cryogenic conditions possesses the given characteristics and therefore constitutes a prominent single-photon source. Nevertheless, the implementation of such a single-photon source requires a complex experimental setup involving a cryostat with a confocal microscope for the effective collection of the molecular emission. In the approach presented here we use a single emitter coupled directly to the end facet of an optical fiber. This has the potential to transfer a single-photon source based on a quantum emitter from a proof-of-principle type of setup to a scalable ``plug-and-play'' device. We present successful coupling of a single organic molecule to an optical fiber and record the excitation spectrum, measure the saturation curve, and analyze the contributions of Raman background fluorescence. The single-photon nature is proven by an antibunched autocorrelation recording, which reveals coherent Rabi oscillations.
Summary form only given. Efficient quantum light sources and non-linear optical elements at the few photon level are the basic ingredients for most applications in nano and quantum technologies. On the other hand, a scalable platform for quantum information and communication typically requires reliable light matter interfaces and on-chip integration. In this work we demonstrate the potential of a novel hybrid technology which combines single organic molecules as quantum emitters and dielectric chips, consisting of ridge waveguides and grating far-field couplers [1].Here the emitters are integrated by spin-coating onto the photonic chip. We demonstrate at room temperature the emission of single photons from DBT molecules into ridge waveguides with a branching ratio up to 40%. The overall single-photon source efficiency, including emission into the guided mode, propagation losses, and emission into a quasi-gaussian mode in free space, is estimated around 16%. These results are competitive with state-of-the-art single photon emission into propagating guided modes from solid state systems [4], while offering a novel platform with unprecedented versatility. Single waveguided photons can be readily processed on-chip or efficiently extracted into a quasi-gaussian mode in free space. We also discuss options to further improve the collection efficiency and applications to quantum optics [5] and to study manybody-induced quantum correlation effects [6].