Single photon emitters are quantum light sources that can enable a variety of quantum based technologies such as quantum information or quantum random number generation, among others. These single photon emitters can have their brightness increased by coupling to a plasmonic cavity. In this work, this possibility is addressed by spin coating anthracene crystals hosting dibenzoterrylene (DBT) molecules on top of Au dipolar nanoantenna arrays. Thin anthracene crystals covering a big fraction of the nanoantenna arrays were achieved, on which confocal fluorescence microscopy and time correlated single photon counting have been used to characterize the emitters. A time gating based analysis has been used to separate the nanoantenna luminescence from the fluorescence of the DBT molecules, obtaining lifetime values from coupled and uncoupled molecules. A set of 149 coupled molecules and 158 uncoupled molecules was represented in a histogram, showing a distribution from whose mean values the lifetime of DBT molecules (t=4.37 ns) was acquired, as well as a mean lifetime reduction of 2.4 times and a maximum lifetime reduction of 7 times.
Single photon emitters are quantum light sources that can enable a variety of quantum based technologies such as quantum information or quantum random number generation, among others. These single photon emitters can have their brightness increased by coupling to a plasmonic cavity. In this work, this possibility is addressed by spin coating anthracene crystals hosting dibenzoterrylene (DBT) molecules on top of Au dipolar nanoantenna arrays. Thin anthracene crystals covering a big fraction of the nanoantenna arrays were achieved, on which confocal fluorescence microscopy and time correlated single photon counting have been used to characterize the emitters. A time gating based analysis has been used to separate the nanoantenna luminescence from the fluorescence of the DBT molecules, obtaining lifetime values from coupled and uncoupled molecules. A set of 149 coupled molecules and 158 uncoupled molecules was represented in a histogram, showing a distribution from whose mean values the lifetime of DBT molecules (t=4.37 ns) was acquired, as well as a mean lifetime reduction of 2.4 times and a maximum lifetime reduction of 7 times.
Single organic molecules hold great promise for generating, manipulating, and storing single photons. Such processes form the basis for new quantum-enhanced technologies such as sensing, communications, and computation. In this talk I will focus on a particularly promising molecule – dibenzoterrylene (DBT). When DBT is introduced into a solid crystal of anthracene it is photostable and emits light between 780 and 795 nm. When cooled to cryogenic temperature, DBT is isolated from phonon-induced dephasing meaning that the photons have a lifetime-limited. I will present recent results in growing DBT-doped anthracene crystals, introducing these to nanophotonic interfaces for enhancing the collection of photons, tuning the DBT emission wavelength to coincide with rubidium atomic absorption, and finally pump-probe spectroscopy experiments to find long-lived triplet states in DBT which will be useful for building a single-molecule quantum memory.
Dibenzoterrylene (DBT) molecules embedded in an anthracene host crystal are promising sources of single photons. They have high photostability and can be readily included in photonic structures [1] . Furthermore, when cooled to cryogenic temperatures they are spectrally stable and display fully coherent, lifetime-limited emission in the zero-phonon line (ZPL) [2] , and have a large branching ratio for this decay compared to incoherent decay involving molecular vibrations [3] . Another key characteristic of DBT-based photon sources is the proximity of their emission wavelength compared to rubidium atoms [4] , which can be exploited for quantum technology applications. However, so far fine-tuning of the emission of DBT has mainly been achieved using Stark tuning with a static electric field.
The physical realisation of a photonic quantum computer requires a reliable, fast, ondemand source of single indistinguishable photons. A promising candidate for one of these sources is a single dye molecule in a solid state matrix placed within the evanescent field of a photonic waveguide. This thesis explores the possibility of coupling of single dibenzoterrylene (DBT) molecules in an anthracene matrix to a silicon nitride waveguide at room temperature. I first discuss the theory by which photons from a DBT molecule can be evanescently coupled to a ridge waveguide. I present a novel growth method to form DBT-doped anthracene crystals which is very promising for applications to photonic devices. I discuss the methodology and the theory of such growth. I describe the confocal microscope I developed and used to image and characterise the emission of the single DBT molecules embedded in these crystals. My measurements show that the molecules are extremely stable single quantum emitters with a well-de ned polarization relative to the crystal axes. Measurements of the saturation intensity at room temperature allow me to estimate that a single DBT molecule could deliver at least 1012 photons before bleaching. This method of growth was used to deposit DBT molecules on top of a silicon nitride ridge waveguide. The results of the coupling experiment are shown. These include confocal images, saturation and lifetime measurements. The coupling efficiency is calculated and compared to what was simulated. The challenges of such structures are then presented. To tackle these challenges I deposited the molecules on top of lithium niobate and in silicon nitride slots. I conclude with a proposal for constructing the best photonic structure which would guarantee an easy deposition of the molecules and high coupling efficiencies.
Single photons are highly desirable for encoding, sending and processing quantum information. Suitable engineering of single quantum emitters and their environment can lead to a reliable single photon source and to mediated photon-photon interactions, essential assets for quantum communication and computation purposes. Dye molecules, our chosen single quantum emitter, have attracted much attention in recent years due to their high photostability and narrow emission lines. In this thesis I present a detailed analysis of the optical properties of single dibenzoterrylene molecules in an anthracene matrix. Single photon emission is demonstrated at room and cryogenic temperatures. In the latter case, an analysis of the second-order correlation function of the emission of a single molecule is studied at various temperatures. The data agree with a full solution of the optical Bloch equations over a wide range of temperature, and provide some insight into the dephasing process of the molecules. I then present a technique for integrating single dye molecules with nano-photonic devices. These are hybrid plasmonic waveguides, designed to guide light and to enhance the interaction with a single emitter by a tight confinement of the waveguide mode. Single molecules are deposited over the waveguides and a first evidence of coupling is presented. I conclude with proposed improvements to the optical setup and to the deposition methods. Finally, I present another type of integrated device, where the light matter interaction is enhanced by inserting single quantum emitters into coupled optical resonators. The theoretical description for the case of resonant two-photon absorption from single atoms in coupled photonic crystal cavities is developed. I conclude by proposing a possible realisation of this system, and describing the first steps towards the fabrication of such a device.
Cavity quantum electrodynamics is the art of enhancing light-matter interaction of photon emitters in cavities with opportunities for sensing, quantum information, and energy capture technologies. To boost emitter-cavity interaction, that is, coupling strength g, ultrahigh quality cavities have been concocted yielding photon trapping times of microsecondsy to milliseconds. However, such high- Q cavities give poor photon output, hindering applications. To preserve high photon output, it is advantageous to strive for highly localized electric fields in radiatively lossy cavities. Nanophotonic antennas are ideal candidates combining low- Q factors with deeply localized mode volumes, allowing large g, provided the emitter is positioned exactly right inside the nanoscale mode volume. Here, with nanometer resolution, we map and tune the coupling strength between a dipole nanoantenna-cavity and a single molecule, obtaining a coupling rate of g max ∼ 200 GHz. Together with accelerated single photon output, this provides ideal conditions for fast and pure nonclassical single photon emission with brightness exceeding 10 9 photons/sec. Clearly, nanoantennas acting as “bad” cavities offer an optimal regime for strong coupling g to deliver bright on-demand and ultrafast single photon nanosources for quantum technologies.
Single photons are very attractive for quantum information processing, given their long coherence time and their ability to carry information in many degrees of freedom. A current challenge is the generation of single photons in a photonic chip in order to scale up the complexity of quantum operations. Solid state emitters could offer this possibility. Quantum dots are one promising approach, but photons produced by different dots are generally distinguishable. Nitrogen-vacancy (N-V) centres in diamond are also promising, however it is challenging to place these in photonic circuits and the emitted photons have many frequencies. By contrast, dibenzoterrylene (DBT) molecules embedded in a thin film of anthracene (AC) at cryogenic temperatures produce a high yield of indistinguishable photons [1, 2]. DBT acts as a two-level system with a narrow 30 MHz near-infrared (785 nm) zero-phonon line [1]. We have proposed that a DBT molecule, deposited in the vicinity of a nanoscale waveguide, could emit these photons efficiently into the waveguide [3]. Conventional spin-coating methods [1] do not offer sufficient control over the surface coverage and the morphology of the AC crystal for deposition on photonic structures, while crystals grown with sublimation are too thick. Another method is needed.