92 research outputs found
Generating single photons at gigahertz modulation-speed using electrically controlled quantum dot microlenses
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 108, 021104 (2016) and may be found at https://doi.org/10.1063/1.4939658.We report on the generation of single-photon pulse trains at a repetition rate of up to 1 GHz. We achieve this speed by modulating the external voltage applied on an electrically contacted quantum dot microlens, which is optically excited by a continuous-wave laser. By modulating the photoluminescence of the quantum dot microlens using a square-wave voltage, single-photon emission is triggered with a response time as short as (281 ± 19) ps, being 6 times faster than the radiative lifetime of (1.75 ± 0.02) ns. This large reduction in the characteristic emission time is enabled by a rapid capacitive gating of emission from the quantum dot, which is placed in the intrinsic region of a p-i-n-junction biased below the onset of electroluminescence. Here, since our circuit acts as a rectifying differentiator, the rising edge of the applied voltage pulses triggers the emission of single photons from the optically excited quantum dot. The non-classical nature of the photon pulse train generated at GHz-speed is proven by intensity autocorrelation measurements with g(2)(0) = 0.3 ± 0.1. Our results combine optical excitation with fast electrical gating and thus show promise for the generation of indistinguishable single photons at rates exceeding the limitations set by the intrinsic radiative lifetime.BMBF, 03V0630, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die Quanteninformationstechnologie (QSOURCE)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots
Quantum dots are arguably the best interface between matter spin qubits and
flying photonic qubits. Using quantum dot devices to produce joint
spin-photonic states requires the electronic spin qubits to be stored for
extended times. Therefore, the study of the coherence of spins of various
quantum dot confined charge carriers is important both scientifically and
technologically. In this study we report on spin relaxation measurements
performed on five different forms of electronic spin qubits confined in the
very same quantum dot. In particular, we use all optical techniques to measure
the spin relaxation of the confined heavy hole and that of the dark exciton - a
long lived electron-heavy hole pair with parallel spins. Our measured results
for the spin relaxation of the electron, the heavy-hole, the dark exciton, the
negative and the positive trions, in the absence of externally applied magnetic
field, are in agreement with a central spin theory which attributes the
dephasing of the carriers' spin to their hyperfine interactions with the
nuclear spins of the atoms forming the quantum dots. We demonstrate that the
heavy hole dephases much slower than the electron. We also show, both
experimentally and theoretically, that the dark exciton dephases slower than
the heavy hole, due to the electron-hole exchange interaction, which partially
protects its spin state from dephasing.Comment: 12 pages, 5 figures, 1 tabl
Impact of Immunization Technology and Assay Application on Antibody Performance – A Systematic Comparative Evaluation
Antibodies are quintessential affinity reagents for the investigation and determination of a protein's expression patterns, localization, quantitation, modifications, purification, and functional understanding. Antibodies are typically used in techniques such as Western blot, immunohistochemistry (IHC), and enzyme-linked immunosorbent assays (ELISA), among others. The methods employed to generate antibodies can have a profound impact on their success in any of these applications. We raised antibodies against 10 serum proteins using 3 immunization methods: peptide antigens (3 per protein), DNA prime/protein fragment-boost (“DNA immunization”; 3 per protein), and full length protein. Antibodies thus generated were systematically evaluated using several different assay technologies (ELISA, IHC, and Western blot). Antibodies raised against peptides worked predominantly in applications where the target protein was denatured (57% success in Western blot, 66% success in immunohistochemistry), although 37% of the antibodies thus generated did not work in any of these applications. In contrast, antibodies produced by DNA immunization performed well against both denatured and native targets with a high level of success: 93% success in Western blots, 100% success in immunohistochemistry, and 79% success in ELISA. Importantly, success in one assay method was not predictive of success in another. Immunization with full length protein consistently yielded the best results; however, this method is not typically available for new targets, due to the difficulty of generating full length protein. We conclude that DNA immunization strategies which are not encumbered by the limitations of efficacy (peptides) or requirements for full length proteins can be quite successful, particularly when multiple constructs for each protein are used
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