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Observation of extremely slow hole spin relaxation in self-assembled quantum dots  [PDF]
D. Heiss,S. Schaeck,H. Huebl,M. Bichler,G. Abstreiter,J. J. Finley,D. V. Bulaev,Daniel Loss
Physics , 2007, DOI: 10.1103/PhysRevB.76.241306
Abstract: We report the measurement of extremely slow hole spin relaxation dynamics in small ensembles of self-assembled InGaAs quantum dots. Individual spin orientated holes are optically created in the lowest orbital state of each dot and read out after a defined storage time using spin memory devices. The resulting luminescence signal exhibits a pronounced polarization memory effect that vanishes for long storage times. The hole spin relaxation dynamics are measured as a function of external magnetic field and lattice temperature. We show that hole spin relaxation can occur over remarkably long timescales in strongly confined quantum dots (up to ~270 us), as predicted by recent theory. Our findings are supported by calculations that reproduce both the observed magnetic field and temperature dependencies. The results suggest that hole spin relaxation in strongly confined quantum dots is due to spin orbit mediated phonon scattering between Zeeman levels, in marked contrast to higher dimensional nanostructures where it is limited by valence band mixing.
Time-Resolved Photoluminescence Spectroscopy: A Novel Technique for Determination of Luminescence of Quantum Dots
Time-Resolved Photoluminescence Spectroscopy: A Novel Technique for Determination of Luminescence of Quantum Dots

ZHENG Zhu-Hong,SHEN De-Zhen,
郑著宏
,申德振

中国物理快报 , 2007,
Abstract: The time-resolved photoluminescence (PL) spectroscopy measured by thegradually increasing start delay time is utilized as a tool for the determination of the luminescence of quantum dots (QDs). The luminescence evolution of self-assembled CdSe QDs during the luminescence decay is fully revealed in terms of the experiment technique. The characteristic narrow luminescence lines of self-assembled CdSe QDs are obtained with increasing start delay time.
Superradiance  [PDF]
Richard Brito,Vitor Cardoso,Paolo Pani
Physics , 2015, DOI: 10.1007/978-3-319-19000-6
Abstract: Superradiance is a radiation enhancement process that involves dissipative systems. With a 60 year-old history, superradiance has played a prominent role in optics, quantum mechanics and especially in relativity and astrophysics. In General Relativity, black-hole superradiance is permitted by dissipation at the event horizon, that allows for energy, charge and angular momentum extraction from the vacuum, even at the classical level. Black-hole superradiance is intimately connected to the black-hole area theorem, Penrose process, tidal forces and even Hawking radiation, which can be interpreted as a quantum version of black-hole superradiance. Various mechanisms (as diverse as massive fields, magnetic fields, anti-de Sitter boundaries, nonlinear interactions, etc...) can confine the amplified radiation and give rise to strong instabilities. These "black-hole bombs" have applications in searches of dark matter and of physics beyond the Standard Model, are associated to the threshold of formation of new black hole solutions that evade the no-hair theorems, can be studied in the laboratory by devising analog models of gravity, and might even provide a holographic description of spontaneous symmetry breaking and superfluidity through the gauge-gravity duality. This work is meant to provide a unified picture of this multifaceted subject, which was missing in the literature. We focus on the recent developments in the field, and work out a number of novel examples and applications, ranging from fundamental physics to astrophysics.
Probing microwave capacitance of self-assembled quantum dots  [PDF]
Guanglei Cheng,Jeremy Levy,Gilberto Medeiros-Ribeiro
Physics , 2009,
Abstract: Self-assembled quantum dots have remarkable optical, electronic and spintronic properties that make them leading candidates for quantum information technologies. Their characterization requires rapid and local determination of both charge and spin degrees of freedom. We present a way to probe the capacitance of small ensembles of quantum dots at microwave frequencies. The technique employs a capacitance sensor based on a microwave microstrip resonator with sensitivity ~10^(-19) F/rt(Hz), high enough to probe single electrons. The integration of this design in a scanning microscope will provide an important tool for investigating single charge and spin dynamics in self-assembled quantum dot systems.
Size dependent exciton g-factor in self-assembled InAs/InP quantum dots  [PDF]
N. A. J. M. Kleemans,J. van Bree,M. Bozkurt,P. J. van Veldhoven,P. A. Nouwens,R. N?tzel,A. Yu. Silov,M. E. Flatté,P. M. Koenraad
Physics , 2008, DOI: 10.1103/PhysRevB.79.045311
Abstract: We have studied the size dependence of the exciton g-factor in self-assembled InAs/InP quantum dots. Photoluminescence measurements on a large ensemble of these dots indicate a multimodal height distribution. Cross-sectional Scanning Tunneling Microscopy measurements have been performed and support the interpretation of the macro photoluminescence spectra. More than 160 individual quantum dots have systematically been investigated by analyzing single dot magneto-luminescence between 1200nm and 1600 nm. We demonstrate a strong dependence of the exciton g-factor on the height and diameter of the quantum dots, which eventually gives rise to a sign change of the g-factor. The observed correlation between exciton g-factor and the size of the dots is in good agreement with calculations. Moreover, we find a size dependent anisotropy splitting of the exciton emission in zero magnetic field.
Influence of ZnTe based distributed Bragg reflectors on the yellow range luminescence of self assembled CdTe QDs  [PDF]
Jean-Guy Rousset,Jakub Kobak,El?bieta Janik,Magdalena Parlinska-Wojtan,Tomasz S?upinski,Jan Suffczyński,Andrzej Golnik,Piotr Kossacki,Micha? Nawrocki,Wojciech Pacuski
Physics , 2014,
Abstract: The influence of a distributed Bragg reflector composed of ZnTe, MgTe, and MgSe superlattices on photoluminescence of self assembled CdTe quantum dots (QD) emitting in the yellow spectral range is investigated. In the case of QDs grown on a distributed Bragg reflector the photoluminescence intensity is enhanced by more than one order of magnitude, whereas the single QD lines are broadened as compared to the case of QDs grown on a ZnTe buffer. Structural and chemical analysis reveal an unintentional formation of a thin ZnSe layer induced by the growth interruption needed for the deposition of the QDs sheet. Sharp emission lines from individual quantum dots are recovered in the case of a thicker ZnTe layer grown prior to the QDs. This indicates that growth interruptions might be responsible for the QD emission line broadening.
Photon-photon correlation statistics in the collective emission from ensembles of self-assembled quantum dots  [PDF]
Fitria Miftasani,Pawe? Machnikowski
Physics , 2014,
Abstract: We present a theoretical analysis of the intensity autocorrelation for the spontaneous emission from a planar ensemble of self-assembled quantum dots. Using the quantum jump approach, we numerically simulate the evolution of the system and construct photon-photon delay time statistics that approximates the second order correlation function of the field. The form of this correlation function in the case of collective emission from a highly homogeneous ensemble qualitatively differs form that characterizing an ensemble of independent emitters (inhomogeneous ensemble of uncoupled dots). The signatures of collective emission in the intensity correlations are observed also in the case of an inhomogeneous but sufficiently strongly coupled ensemble. Thus, we show that the second order correlation function of the emitted field provides a sensitive test of cooperative effects.
Polarization properties of excitonic qu-bits in single self-assembled quantum dots  [PDF]
C. Tonin,R. Hostein,V. Voliotis,R. Grousson,A. Lemaitre,A. Martinez
Physics , 2011, DOI: 10.1103/PhysRevB.85.155303
Abstract: We investigate polarization properties of neutral exciton emission in single self-assembled InAs/GaAs quantum dots. The in-plane shape and strain anisotropy strongly couple the heavy and light hole states and lead to large optical anisotropy with non-orthogonal linearly polarized states misaligned with respect to the crystallographic axes. Owing to a waveguiding experimental configuration, luminescence polarization along the growth axis has been observed revealing the presence of shear components of the deformation tensor out of the growth plane. Resonant luminescence experiments allowed determining the oscillator strength ratio of the two exciton eigenstates. Valence band mixing governs this ratio and can be very different from dot to dot, however the polarization anisotropy axis is quite fixed inside a scanned area of one \mum^{2} and indicates that the in-plane deformation direction to which it is related has a correlation length of the order of magnitude of one \mum^{2}.
Spin superradiance versus atomic superradiance  [PDF]
V. I. Yukalov
Physics , 2005, DOI: 10.1002/lapl.200510002
Abstract: A comparative analysis is given of spin superradiance and atomic superradiance. Their similarities and distinctions are emphasized. It is shown that, despite a close analogy, these phenomena are fundamentally different. In atomic systems, superradiance is a self-organized process, in which both the initial cause, being spontaneous emission, as well as the collectivizing mechanism of their interactions through the common radiation field, are of the same physical nature. Contrary to this, in actual spin systems with dipole interactions, the latter are the major reason for spin motion. Electromagnetic spin interactions through radiation are negligible and can never produce collective effects. The possibility of realizing superradiance in molecular magnets by coupling them to a resonant circuit is discussed.
Dynamics of quantum dot superradiance  [PDF]
V. I. Yukalov,E. P. Yukalova
Physics , 2010, DOI: 10.1103/PhysRevB.81.075308
Abstract: The possibility of realizing the superradiant regime of electromagnetic emission by the assembly of quantum dots is considered. The overall dynamical process is analyzed in detail. It is shown that there can occur several qualitatively different stages of evolution. The process starts with dipolar waves triggering the spontaneous radiation of individual dots. This corresponds to the fluctuation stage, when the dots are not yet noticeably correlated with each other. The second is the quantum stage, when the dot interactions through the common radiation field become more important, but the coherence is not yet developed. The third is the coherent stage, when the dots radiate coherently, emitting a superradiant pulse. After the superradiant pulse, the system of dots relaxes to an incoherent state in the relaxation stage. If there is no external permanent pumping, or the effective dot interactions are weak, the system tends to a stationary state during the last stationary stage, when coherence dies out to a low, practically negligible, level. In the case of permanent pumping, there exists the sixth stage of pulsing superradiance, when the system of dots emits separate coherent pulses.
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