The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Gjerrit Meinsma - One of the best experts on this subject based on the ideXlab platform.
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On /spl Hscr//sub /spl infin// control for dead-Time systems
IEEE Transactions on Automatic Control, 2000Co-Authors: Gjerrit Meinsma, Hans ZwartAbstract:A mixed sensitivity H∞ problem is solved for dead-Time systems. It is shown that for a given bound on the H∞-norm causal stabilizing controllers exist that achieve this bound if and only if a related finite-dimensional Riccati equation has a solution with a certain nonsingularity property. In the case of Zero Time Delay, the Riccati equation is a standard Riccati equation and the nonsingularity condition is that the solution be nonnegative definite. For nonZero Time Delay, the nonsingularity condition is more involved but still allows us to obtain controllers. All suboptimal controllers are parameterized, and the central controller is shown to be a feedback interconnection of a finite-dimensional system and a finite memory system, both of which can be implemented. Some H∞ problems are rewritten as pure rational H∞ problems using a Smith predictor parameterization of the controlle
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Robustness of the stability of feedback systems with respect to small Time Delays
Systems & Control Letters, 1999Co-Authors: Gjerrit Meinsma, Tetsuya IwasakiAbstract:It is shown that a feedback system is robustly stable with respect to small Time Delays if and only if it is stable for Zero Time Delay and a structured singular value is less than one.
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On H-infinity control for dead-Time systems
1997Co-Authors: Gjerrit Meinsma, Heiko J. ZwartAbstract:A mixed sensitivity H-infinity problem is solved for dead-Time systems. It is shown that for a given bound on the H-infinity-norm causal stabilizing controllers exist that achieve this bound if and only if a related finite-dimensional Riccati equation has a solution with a certain nonsingularity property. In the case of Zero Time Delay, the Riccati equation is a standard Riccati equation and the nonsingularity condition is that the solution be nonnegative definite. For nonZero Time Delay, the nonsingularity condition is more involved but still allows us to obtain controllers. All suboptimal controllers are parameterized, and the central controller is shown to be a feedback interconnection of a finite-dimensional system and a finite memory system, both of which can be implemented. Some H-infinity problems are rewritten as pure rational H-infinity problems using a Smith predictor parameterization of the controller
Tomas Jemsson - One of the best experts on this subject based on the ideXlab platform.
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Time Correlated Single Photon Spectroscopy on Pyramidal Quantum Dots - Time Correlated Single Photon Spectroscopy on Pyramidal Quantum Dots
2015Co-Authors: Tomas JemssonAbstract:We report on excitonic single photon emission and biexcitonic photon bunching from an InGaN quantum dot formed on the apex of a hexagonal GaN micropyramid. An approach to suppress uncorrelated emission from the pyramid base is proposed, a metal lm is demonstrated to eectively screen background emission and thereby signicantly enhance the signal-to-background ratio of the quantum dot emission. As a result, the second order coherence function at Zero Time Delay g(2)(0) is signicantly reduced (to g(2)(0) = 0.24, raw value) for the excitonic autocorrelation at a temperature of 12 K under continuous wave excitation, and a dominating single photon emission is demonstrated to survive up to 50 K. The deterioration of the g(2)(0)-value at elevated temperatures is well understood as the combined eect of reduced signal-to-background ratio and limited Time resolution of the setup. This result underlines the great potential of site controlled pyramidal dots as sources of fast polarized single photons.
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Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid.
Nanotechnology, 2015Co-Authors: Tomas Jemsson, H. Machhadani, Per-olof Holtz, K. Fredrik KarlssonAbstract:We report on excitonic single photon emission and biexcitonic photon bunching from an InGaN quantum dot formed on the apex of a hexagonal GaN micropyramid. An approach to suppress uncorrelated emission from the pyramid base is proposed, a metal film is demonstrated to effectively screen background emission and thereby significantly enhance the signal-to-background ratio of the quantum dot emission. As a result, the second order coherence function at Zero Time Delay is significantly reduced (to = 0.24, raw value) for the excitonic autocorrelation at a temperature of 12 K under continuous wave excitation, and a dominating single photon emission is demonstrated to survive up to 50 K. The deterioration of the -value at elevated temperatures is well understood as the combined effect of reduced signal-to-background ratio and limited Time resolution of the setup. This result underlines the great potential of site-controlled pyramidal dots as sources of fast polarized single photons.
Steven S Vogel - One of the best experts on this subject based on the ideXlab platform.
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measuring two photon microscopy ultrafast laser pulse duration at the sample plane using Time correlated single photon counting
Journal of Biomedical Optics, 2020Co-Authors: Steven S VogelAbstract:Two-photon microscopy (2PM) has revolutionized biomedical imaging by allowing thin optical sectioning in relatively thick biological specimens. Because dispersive microscope components in 2PM, such as objective lens, can alter temporal laser pulse width (typically being broader at the sample plane), for accurate measurements of two-photon absorption properties, it is important to characterize pulse duration at the sample plane. We present a simple modification to a two-photon microscope light path that allows for second-harmonic-generation-based interferometric autocorrelation measurements to characterize ultrafast laser pulse duration at the sample plane using Time-correlated single-photon counting (TCSPC). We show that TCSPC can be used as a simple and versatile method to estimate the Zero Time Delay step value between two adjacent ultrafast laser pulses for these measurements. To demonstrate the utility of this modification, we measured the Coherent Chameleon-Ultra II Ti:sapphire laser pulse width at the sample plane using a 10 × air, 40 × air, or 63 × water-immersion objective lens. At 950-nm two-photon excitation, the measured pulse width was 154 ± 32, 165 ± 13, and 218 ± 27 fs ( n = 6, mean ± standard deviation), respectively.
Dario Gerace - One of the best experts on this subject based on the ideXlab platform.
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Optimal antibunching in passive photonic devices based on coupled nonlinear resonators
New Journal of Physics, 2013Co-Authors: S. Ferretti, Vincenzo Savona, Dario GeraceAbstract:We propose the use of weakly nonlinear passive materials for prospective applications in integrated quantum photonics. It is shown that strong enhancement of native optical nonlinearities by electromagnetic field confinement in photonic crystal resonators can lead to single-photon generation only exploiting the quantum interference of two coupled modes and the effect of photon blockade under resonant coherent driving. For realistic system parameters in state of the art microcavities, the efficiency of such a single-photon source is theoretically characterized by means of the second-order correlation function at Zero-Time Delay as the main figure of merit, where major sources of loss and decoherence are taken into account within a standard master equation treatment. These results could stimulate the realization of integrated quantum photonic devices based on non-resonant material media, fully integrable with current semiconductor technology and matching the relevant telecom band operational wavelengths, as an alternative to single-photon nonlinear devices based on cavity quantum electrodynamics with artificial atoms or single atomic-like emitters.
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Single-photon nonlinear optics with Kerr-type nanostructured materials
Physical Review B, 2012Co-Authors: S. Ferretti, Dario GeraceAbstract:We employ a quantum theory of the nonlinear optical response from an actual solid-state material possessing an intrinsic bulk contribution to the third-order nonlinear susceptibility (Kerr-type nonlinearity), which can be arbitrarily nanostructured to achieve diffraction-limited electromagnetic field confinement. By calculating the Zero-Time Delay second-order correlation of the cavity field, we set the conditions for using semiconductor or insulating materials with near-infrared energy gaps as efficient means to obtain single-photon nonlinear behavior in prospective solid-state integrated devices, alternative to ideal sources of quantum radiation such as, e.g., single two-level emitters.Comment: 5 pages, three figure
Weidong Geng - One of the best experts on this subject based on the ideXlab platform.
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Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System
Scientific reports, 2015Co-Authors: Jing Tang, Weidong GengAbstract:We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at Zero Time Delay g((2))(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing.
