A single-photon source is an essential tool for the emerging field of quantum technologies. Ideally, it should be spectrally compatible with other photonic systems while providing a high flux of narrow-band photons. The single organic dye molecule dibenzanthantherene (DBATT) embedded into a n-tetradecane Spol’skii matrix under cryogenic conditions possesses the given characteristics, thus constitutes a prominent single-photon source. Nevertheless, the implementation of such a single-photon source requires an elaborate experimental setup involving a cryostat with a confocal microscope for the effective collection of the molecule’s emission. Another approach is to use a single emitter coupled to an optical fiber. This approach has the potential to transfer a single-photon source from a proof-of-principle type of setup to a scalable “plug and play” device. Here we present the alignment-free fiber-coupled organic molecule single-photon source cooled down to cryogenic temperatures using a transport dewar as a cryostat.
A single-photon source is an essential tool for the emerging field of quantum technologies. Ideally, it should be spectrally compatible with other photonic systems while providing a high flux of narrow-band photons. The single organic dye molecule dibenzanthantherene (DBATT) embedded into a n-tetradecane Spol’skii matrix under cryogenic conditions possesses the given characteristics, thus constitutes a prominent single-photon source. Nevertheless, the implementation of such a single-photon source requires an elaborate experimental setup involving a cryostat with a confocal microscope for the effective collection of the molecule’s emission. Another approach is to use a single emitter coupled to an optical fiber. This approach has the potential to transfer a single-photon source from a proof-of-principle type of setup to a scalable “plug and play” device. Here we present the alignment-free fiber-coupled organic molecule single-photon source cooled down to cryogenic temperatures using a transport dewar as a cryostat.
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.
Placing single emitters inside optical cavities provides a way of drastically modifying their interaction with the electric field. Such systems can be used to test our fundamental understanding of quantum electrodynamics and to develop devices that exploit this new found knowledge. This thesis describes work towards coupling single dye molecules to optical fibre microcavities at cryogenic temperatures. I present the design of an oven growth chamber and develop a method to grow cosublimated crystals of anthracene doped with dibenzoterrylene. I then describe the characterisation of these samples using a confocal microscope setup both at ambient and cryogenic temperatures. The samples grown show bright, stable, single emitters in a defined orientation in the anthracene crystals. By varying the growth parameters of the homebuilt crystal growing chamber, we can control the density of dibenzoterrylene molecules and grow at an optimum density to use these crystals in conjunction with optical fibre microcavities. I show how optical fibre microcavities have been developed that can be cooled to the liquid helium temperatures required to take advantage of the lifetime-limited emission from single dibenzoterrylene molecules, that only occurs below 4K. I also present cavity quantum electrodynamic simulations of the cavities, showing what we expect to see when we take reflection spectra of single molecules coupled to these cavities. In addition, I describe the optical setup that has been developed to take these measurements. I conclude with proposed improvements to the cavity setup that will enable these reflection spectra to be more easily taken. This will allow these molecule-cavity systems to be used as infrared single photon sources for quantum optics experiments.
At cryogenic temperatures, organic single-photon sources (SPSs) offer Fourier-limited emission, virtually unlimited photostability, and emission wavelengths selectable by molecular design, making them attractive for quantum metrology, secure communication, and photonic quantum information processing. However, their efficient integration with photonic microstructures has remained challenging, limiting photon collection from single organic emitters under cryogenic operation. Here, we demonstrate a cryogenic planar metallo-dielectric antenna that efficiently directs the emission of a single dibenzoterrylene (DBT) molecule towards the collection optics. The device reaches a collection efficiency of 97% and delivers 100 million photons per second into the first lens. We measure a photon indistinguishability for the Fourier-limited transition of 91.2% while maintaining a high single-photon purity of 97.7% under strong continuous-wave (CW) and pulsed excitation. These results establish organic molecules as a high-performance platform for single-photon generation and represent an important step towards scalable organic quantum photonic technologies.
Abstract In this work, we present a stand-alone and fiber-coupled quantum-light source. The plug-and-play device is based on an optically driven quantum dot delivering single photons via an optical fiber. The quantum dot is deterministically integrated in a monolithic microlens which is precisely coupled to the core of an optical fiber via active optical alignment and epoxide adhesive bonding. The rigidly coupled fiber-emitter assembly is integrated in a compact Stirling cryocooler with a base temperature of 35 K. We benchmark our practical quantum device via photon auto-correlation measurements revealing g(2)(0) = 0.07 ± 0.05 under continuous-wave excitation and we demonstrate triggered non-classical light at a repetition rate of 80 MHz. The long-term stability of our quantum light source is evaluated by endurance tests showing that the fiber-coupled quantum dot emission is stable within 4% over several successive cool-down/warm-up cycles. Additionally, we demonstrate non-classical photon emission for a user-intervention-free 100-hour test run and stable single-photon count rates up to 11.7 kHz with a standard deviation of 4%.
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.
Single-photon sources (SPS) are essential for secure quantum communication and quantum computing. Solid-state systems based on quantum dots (QDs) are particularly attractive for emitting pure, on-demand single photons, making them ideal candidates for flying qubits in quantum key distribution protocols. Integrating a SPS into photonic circuits is a key step toward scalable and "plug-and-play" quantum technologies. However, the SPS with the best performances (III-V QDs) operate only at cryogenic temperatures, a significant drawback for practical implementation. Alternatively, CdSe QDs (II-VI) are operational at 300 K and emit in the blue-green range, thus allowing for free-space long-distance communication in seawater and air.The thesis aims to develop an on-chip single-photon source that can operate at non-cryogenic temperatures. The SPS consists of a CdSe QD embedded within a ZnSe nanowire (NW) shell grown by molecular beam epitaxy on a patterned GaAs (111)B substrate. The NW geometry enhances light extraction by acting as a single-mode waveguide, while the conical ending of the shell improves emission control.We investigated the optical performance of the as-grown QD-NW emitter at room temperature, achieving a promising brightness of 0.17 photons per pulse and antibunching behavior with g(2)(0) < 0.3 within a reduced spectral window. However, the emission spectrum at 300 K features overlapping broad lines, leading to a trade-off between brightness and purity. At 6 K, we used a broadband filter to capture entirely the narrow exciton line and measured directly the photon count rate with an avalanche photodiode. In addition, we observed strong antibunching with a few percent purity through cathodoluminescence.Phonons impact the performance of the SPS at high temperatures, where broad lines overlap, and at cryogenic temperatures, where they reduce the photon indistinguishability. Understanding and controlling the influence of phonons has increased the need for high-accuracy temperature measurements at cryogenic temperatures. We present a calibration-free method to extract the local temperature from the emission spectrum, which we used to investigate the heating effects induced by non-resonant excitation. Additionally, we analysed the line-broadening mechanisms from cryogenic to room temperature. An extension of the Huang-Rhys model is developed to analytically describe the acoustic exciton-phonon interactions, accounting for multi-phonon processes. The model accurately fits emission spectra from 6 K to 300 K using parameters obtained from low-temperature data.The tapered nanowire shape is also an advantage for integration into a photonic device, enabling efficient evanescent coupling when the emitter is positioned next to a waveguide. The direct transfer using micromanipulators in a scanning electron microscope onto pre-fabricated waveguides is very challenging due to the tiny size of the waveguide at an emission wavelength of 550 nm. We developed a new approach, where the emitter is deposited within a large zone and then embedded within a resist, which serves as a mask during waveguide etching. This method significantly reduces the need for micro-manipulation and allows for promising prospects. We used finite-difference time-domain simulations to support the design and fabrication of the waveguides for optimal coupling.