Connecting excited state lifetime and intensity correlations for quantitative analysis of chromophore interactions

Intensity correlation is a powerful tool to study intensity fluctuations on various time scales. Fluorescence correlation spectroscopy (FCS) is a popular representative to monitor spontaneous intensity fluctuations caused by the deviation of the system from thermal equilibrium at nanomolar concentrations. FCS is frequently used to determine local concentrations, diffusion coefficients and intermolecular interactions of fluorescently labeled biomolecules. However, determination of the forward and backward transition rate constants and thereby also the equilibrium constant is not possible when two intensity levels are involved e.g. in a Förster resonance energy transfer (FRET) experiment. The idea of combining the fluorescence lifetime information (microtime) with the intensity information (macrotime) lead to the development of fluorescence lifetime FCS (FLCS). However, FLCS requires prior knowledge of the fluorescence lifetime components and suffers in experiments from inaccurate bunching amplitudes. Therefore, it is the aim of this work to develop a model free connection between the microtime information and the macrotime information. To this end, shrinking-gate FCS (sg-FCS) is presented which enables the extraction of microscopic transition rate constants without prior knowledge by correlating photon subsets according to their arrival time after pulsed laser excitation. sg-FCS is demonstrated in simulations and in surface- and solution-experiments with a DNA based model system. Without prior knowledge, the equilibrium constant is recovered over two and a half orders of magnitude. Additionally, sg-FCS identifies dynamic bunching amplitudes in the intensity correlation as they come with a change in the fluorescence lifetime which is not the case for on-off switching processes. Beyond the analysis of photon bunching on long timescales, the degree of photon antibunching on short timescales is used as a metric for the number of emitters in a multichromophoric system. So far, the interpretation of antibunching has been hampered by exciton annihilation processes. On the one hand, singlet-singlet annihilation (SSA) increases the degree of photon antibunching. On the other hand, singlet-triplet annihilation (STA) results in photon bunching on longer timescales and the interpretation of photon antibunching in presence of photon bunching was not discussed in literature yet. Here, it is demonstrated in simulations and experiments with DNA origami-based model systems, how photon antibunching is affected by independent and collective chromophore blinking. Additionally, universal guidelines for correct interpretation of photon antibunching are identified. Thereby, the time dependence of the STA process is used to identify collective blinking chromophores by applying the sg-FCS analysis which in addition recovers the STA rate constant. In a similar approach, picosecond time resolved antibunching (psTRAB) also utilizes the excited state lifetime information which is then used to recover the true number of chromophores in a multichromophoric system which is subject to SSA. It is demonstrated in simulations and experiments, that psTRAB can recover the true number of emitters on a DNA origami structure besides efficient SSA. Additionally, the analysis reveals the dimensionality of exciton diffusion in mesoscopic H- and J-type conjugated polymer aggregates. At last, the potential for bright and small point light sources based on DNA origami is evaluated. State of the art dye loaded polymer beads suffer from inhomogeneous fluorescence properties and size. DNA origami provides stoichiometric and spatial control over the dye modifications and is a promising candidate to overcome the drawbacks of polymer beads. To obtain the highest labeling density on DNA origami structures the distance dependency of dye-dye interaction is systematically examined. At small distances, fluorescence lifetime and fluorescence intensity are quenched due to static and dynamic quenching which becomes less for larger distances until the dyes are permanently separated at ~ 3 nm distance. However, the dyes are not independent at this distances and resonant coupling like SSA as well as STA can affect the fluorescence intensity, photoblinking and photostability. All in all, the findings and algorithms described above are easy to apply in many laboratories around the world which are already using TCSPC and will contribute to the quantitative analysis of switching kinetics between intensity states by sg-FCS and the change of independent chromophore numbers over time psTRAB. At last, further consideration of weak and strong coupling effects between organic dyes in close proximity will pave the way to bright and unprecedented homogeneous DNA origami-based point light sources for biophysics experiments and super resolution microscopy

Rectangular Photonic Crystal Nanobeam Cavities in Bulk Diamond

We demonstrate the fabrication of photonic crystal nanobeam cavities with rectangular cross section into bulk diamond. In simulation, these cavities have an unloaded quality factor (Q) of over 1 million. Measured cavity resonances show fundamental modes with spectrometer-limited quality factors larger than 14,000 within 1nm of the NV center's zero phonon line at 637nm. We find high cavity yield across the full diamond chip with deterministic resonance trends across the fabricated parameter sweeps

Benchmarking End-to-end Learning of MIMO Physical-Layer Communication

End-to-end data-driven machine learning (ML) of multiple-input multiple-output (MIMO) systems has been shown to have the potential of exceeding the performance of engineered MIMO transceivers, without any a priori knowledge of communication-theoretic principles. In this work, we aim to understand to what extent and for which scenarios this claim holds true when comparing with fair benchmarks. We study closed-loop MIMO, open-loop MIMO, and multi-user MIMO and show that the gains of ML-based communication in the former two cases can be to a large extent ascribed to implicitly learned geometric shaping and bit and power allocation, not to learning new spatial encoders. For MU-MIMO, we demonstrate the feasibility of a novel method with centralized learning and decentralized executing, outperforming conventional zero-forcing. For each scenario, we provide explicit descriptions as well as open-source implementations of the selected neural-network architectures.Comment: 6 pages, 8 figures, conference pape

A scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid devices

Integrated quantum optical hybrid devices consist of fundamental constituents such as single emitters and tailored photonic nanostructures. A reliable fabrication method requires the controlled deposition of active nanoparticles on arbitrary nanostructures with highest precision. Here, we describe an easily adaptable technique that employs picking and placing of nanoparticles with an atomic force microscope combined with a confocal setup. In this way, both the topography and the optical response can be monitored simultaneously before and after the assembly. The technique can be applied to arbitrary particles. Here, we focus on nanodiamonds containing single nitrogen vacancy centers, which are particularly interesting for quantum optical experiments on the single photon and single emitter level.Comment: The following article has been submitted to Review of Scientific Instruments. After it is published, it will be found at http://rsi.aip.org

Evaluation of nitrogen- and silicon-vacancy defect centres as single photon sources in quantum key distribution

We demonstrate a quantum key distribution (QKD) testbed for room temperature single photon sources based on defect centres in diamond. A BB84 protocol over a short free-space transmission line is implemented. The performance of nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is evaluated and an extrapolation for next-generation sources with enhanced efficiency is discussed.Comment: 14 pages, 5 figure

Klimawandel vor unserer Haustür: Wie sich unser Leben heute bereits verändert = Climate change at our doorstep: How our lives are already changing

DAS REKLIM JUBILÄUMSMAGAZIN berichtet in Geschichten und Bildern von der Themenvielfalt und den Ergebnissen des Forschungsverbundes und erläutert, wie die Wissenschaft im Dialog mit der Gesellschaft arbeitet, um Fragen unserer Zeit aufzugreifen. Lassen Sie sich begeistern! THE REKLIM ANNIVERSARY MAGAZINE reports, in stories and images, on the research network’s findings and broad range of focus areas. In addition, it demonstrates how the research community can and is working in dialogue with society in order to address the most pressing questions of our time. Check it out