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Register a new userEffect of charging on CdSe/CdS dot-in-rods single-photon emission
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The photon statistics of CdSe/CdS dot-in-rods nanocrystals is studied with a method involving post-selection of the photon detection events based on the photoluminescence count rate. We show that flickering between two states needs to be taken into account to interpret the single-photon emission properties. With post-selection we are able to identify two emitting states: the exciton and the charged exciton (trion), characterized by different lifetimes and different second order correlation functions. Measurements of the second order autocorrelation function at zero delay with post- selection shows a degradation of the single photon emission for CdSe/CdS dot-in-rods in a charged state that we explain by deriving the neutral and charged biexciton quantum yields.
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The blinking dynamics of colloidal core-shell CdSe/CdS dot-in-rods is studied in detail at the single particle level. Analyzing the autocorrelation function of the fluorescence intensity, we demonstrate that these nanoemitters are characterized by a short value of the mean duration of bright periods (ten to a few hundreds of microseconds). The comparison of the results obtained for samples with different geometries shows that not only the shell thickness is crucial but also the shape of the dot- in-rods. Increasing the shell aspect ratio results in shorter bright periods suggesting that surface traps impact the stability of the fluorescence intensity.
We prove experimentally, upon polarization analysis performed on a large statistic of single nanoemitters, that high quality core/shell CdSe/CdS dot-in-rods behave as linear dipoles. Moreover, the dipole in-plane and out-of-plane orientations could be assessed. We demonstrate in particular that, contrary to expectations, the emitting dipole is not aligned with the elongated axis of the dot-in-rod. Besides, the polarimetric measurements prove that the excitation transition cannot be approximated by a single linear dipole, contrary to the emission transition. Finally, we highlight that non-radiative channels of charge carrier recombination do not affect the dipolar nature of the radiative transitions.
Single-photon sources based on semiconductor quantum dots have emerged as an excellent platform for high efficiency quantum light generation. However, scalability remains a challenge since quantum dots generally present inhomogeneous characteristics. Here we benchmark the performance of fifteen deterministically fabricated single-photon sources. They display an average indistinguishability of 90.6 +/- 2.8 % with a single-photon purity of 95.4 +/- 1.5 % and high homogeneity in operation wavelength and temporal profile. Each source also has state-of-the-art brightness with an average first lens brightness value of 13.6 +/- 4.4 %. Whilst the highest brightness is obtained with a charged quantum dot, the highest quantum purity is obtained with neutral ones. We also introduce various techniques to identify the nature of the emitting state. Our study sets the groundwork for large-scale fabrication of identical sources by identifying the remaining challenges and outlining solutions.
Colloidal quantum dots (cQDs) are now a mature nanomaterial with optical properties customizable through varying size and composition. However, their use in optical devices is limited as they are not widely available in convenient forms such as optical fibers. With advances in polymerization methods incorporating nanocrystals, nanocomposite materials suitable for processing into high quality hybrid active fibers can be achieved. We demonstrate a plastic optical fiber fabrication method which ensures homogeneous dispersion of cQDs within a polymer core matrix. Loading concentrations between 10$^{11}$-10$^{13}$ CdSe/CdS cQDs per cm$^{3}$ in polystyrene were electronically imaged, confirming only sporadic sub-wavelength aggregates. Rayleigh scattering losses are therefore dominant at energies below the semiconductors band gap, but are overtaken by a sharp CdS-related absorption onset around 525 nm facilitating cQD excitation. The redshifted photoluminescence emission is then minimally reabsorbed along the fiber with a spectrum barely affected by the polymerization and a quantum yield staying at $sim$65$%$ of its initial value. The latter, along with the glass transition temperature and refractive index, is independent of the cQD concentration hence yielding a proportionally increasing light output. Our cQD-doped fibers are photostable to within 5$%$ over days showing great promise for functional material applications.
User-friendly single-photon sources with high photon-extraction efficiency are crucial building blocks for photonic quantum applications. For many of these applications, such as long-distance quantum key distribution, the use of single-mode optical fibers is mandatory, which leads to stringent requirements regarding the device design and fabrication. We report on the on-chip integration of a quantum dot microlens with a 3D-printed micro-objective in combination with a single-mode on-chip fiber coupler. The practical quantum device is realized by deterministic fabrication of the QD-microlens via in-situ electron-beam lithography and 3D two-photon laser writing of the on-chip micro-objective and fiber-holder. The QD with microlens is an efficient single-photon source, whose emission is collimated by the on-chip micro-objective. A second polymer microlens is located at the end facet of the single-mode fiber and ensures that the collimated light is efficiently coupled into the fiber core. For this purpose, the fiber is placed in the on-chip fiber chuck, which is precisely aligned to the QD-microlens thanks to the sub-$mu$m processing accuracy of high-resolution two-photon direct laser writing. This way, we obtain a fully integrated high-quality quantum device with broadband photon extraction efficiency, a single-mode fiber-coupling efficiency of 26%, a single-photon flux of 1.5 MHz at single-mode fibre output and a multi-photon probability of 13 % under pulsed optical excitation. In addition, the stable design of the developed fiber-coupled quantum device makes it highly attractive for integration into user-friendly plug-and-play quantum applications.
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