918 research outputs found
Resonant optical pumping of a Mn spin in a strain free quantum dot
We report on the spin properties of individual Mn atoms in II-VI
semiconductor strain free quantum dots. Strain free Mn-doped CdTe quantum dots
are formed by width fluctuations in thin quantum wells lattice matched on a
CdTe substrate. These quantum dots permit to optically probe and address any
spin state of a Mn atom in a controlled strain environment. The absence of
strain induced magnetic anisotropy prevents an optical pumping of the Mn spin
at zero magnetic field. Thus, a large photoluminescence is obtained under
resonant optical excitation of the exciton-Mn complex. An efficient optical
pumping of the coupled electronic and nuclear spins of the Mn is restored under
a weak magnetic field. The observed reduction of the resonant photoluminescence
intensity under magnetic field is well described by a model including the
hyperfine coupling and a residual crystal field splitting of the Mn atom.
Finally, we show that the second order correlation function of the resonant
photoluminescence presents a large photon bunching at short delay which is a
probe of the dynamics of coupled electronic and nuclear spins of the Mn atom
Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation
We analyze the spin dynamics of an individual magnetic atom (Mn) inserted in
a II-VI semiconductor quantum dot under resonant optical excitation. In
addition to standard optical pumping expected for a resonant excitation, we
show that for particular conditions of laser detuning and excitation intensity,
the spin population can be trapped in the state which is resonantly excited.
This effect is modeled considering the coherent spin dynamics of the coupled
electronic and nuclear spin of the Mn atom optically dressed by a resonant
laser field. This spin population trapping mechanism is controlled by the
combined effect of the coupling with the laser field and the coherent
interaction between the different Mn spin states induced by an anisotropy of
the strain in the plane of the quantum dot
Dynamics of a Mn spin coupled to a single hole confined in a quantum dot
Using the emission of the positively charged exciton as a probe, we analyze
the dynamics of the optical pumping and the dynamics of the relaxation of a Mn
spin exchange-coupled with a confined hole spin in a II-VI semiconductor
quantum dot. The hole-Mn spin can be efficiently initialized in a few tens of
under optical injection of spin polarized carriers. We show that this
optical pumping process and its dynamics are controlled by electron-Mn
flip-flops within the positively charged exciton-Mn complex. The pumping
mechanism and its magnetic field dependence are theoretically described by a
model including the dynamics of the electron-Mn complex in the excited state
and the dynamics of the hole-Mn complex in the ground state of the positively
charged quantum dot. We measure at zero magnetic field a spin relaxation time
of the hole-Mn spin in the range or shorter. This hole-Mn spin
relaxation is induced by the presence of valence band mixing in self-assembled
quantum dots
Strain induced coherent dynamics of coupled carriers and Mn spins in a quantum dot
We report on the coherent dynamics of the spin of an individual magnetic atom
coupled to carriers in a semiconductor quantum dot which has been investigated
by resonant photoluminescence of the positively charged exciton (X+). We
demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single
Mn atom forms an ensemble of optical Lambda systems which can be addressed
independently. We show that the spin dynamics of the X+Mn complex is dominated
by the electron-Mn exchange interaction and report on the coherent dynamics of
the electron-Mn spin system that is directly observed in the time domain.
Quantum beats reflecting the coherent transfer of population between
electron-Mn spin states, which are mixed by an anisotropic strain in the plane
of the quantum dot, are clearly observed. We finally highlight that this strain
induced coherent coupling is tunable with an external magnetic field
Resonant photoluminescence and dynamics of a hybrid Mn-hole spin in a positively charged magnetic quantum dot
We analyze, through resonant photoluminescence, the spin dynamics of an
individual magnetic atom (Mn) coupled to a hole in a semiconductor quantum dot.
The hybrid Mn-hole spin and the positively charged exciton in a CdTe/ZnTe
quantum dot forms an ensemble of systems which can be addressed
optically. Auto-correlation of the resonant photoluminescence and resonant
optical pumping experiments are used to study the spin relaxation channels in
this multilevel spin system. We identified for the hybrid Mn-hole spin an
efficient relaxation channel driven by the interplay of the Mn-hole exchange
interaction and the coupling to acoustic phonons. We also show that the optical
systems are connected through inefficient spin-flips than can be
enhanced under weak transverse magnetic field. The dynamics of the resonant
photoluminescence in a p-doped magnetic quantum dot is well described by a
complete rate equation model. Our results suggest that long lived hybrid
Mn-hole spin could be obtained in quantum dot systems with large
heavy-hole/light-hole splitting
Parameterization Methods and Autoregressive Model
The first phase for the treatment of random signals is the feature extraction; in this we can find several methods for that. In this chapter, we presented the autoregressive (AR) method, some methods of univariate and multivariate measures, and examples of their applications
The corrosive effects of salt spray on electrolytic zinc plated mechanical fasteners: The case of clear chromate and yellow dichromate coatings on medium carbon plated bolts
The purpose of this study was to evaluate the relationship between plating thickness and corrosion resistance of zinc coated medium carbon steel bolts under salt spray moisture conditions. Two types of zinc coatings were chosen for the study: the clear chromate zinc and the yellow dichromate zinc. One hundred and eighty 3/8-16 x 5 3/4 inch medium carbon steel bolts were selected for the test and divided into groups of 18. Two types of salt solution were used in the study: the low salt and the high salt. Bolts with various coatings tested with low salt concentration were composed of groups of 18 with different coating conditions. Bolts with various coatings and tested with high salt concentration solution were composed of groups of 18 each.
An electronic balance was used to take the weight before and after for each sample tested. An electronic thickness tester was also used to measure the thickness before and after for each sample. The hypothesis was supported when P-value of the overall test was less than the set alpha value.
The percentage weight loss, thickness loss, and the analysis of variance or ANOVA were the statistics used to interpret the results of the test.
The conclusions drawn from these tests were:
1. Medium carbon steel bolts plated electrolytically with yellow dichromate zinc were more corrosion resistant than the ones plated with clear chromate zinc.
2. The yellow dichromate zinc appeared to be more protective than the clear chromate zinc.
3. Bolt coatings should be at least 0.0002 thick to guarantee a minimum protection on medium carbon steel bolts.
4. Yellow dichromate zinc was chosen to be the best coating on medium carbon bolts.
5. The clear chromate zinc does not provide a good protection for medium carbon bolts beyond 60 hours in the fog chamber of the salt spray apparatus.
Based on the findings of this study, the following suggestions were made:
1. Manufacturers should be aware of some geographical locations with high moisture content and high pollution in the atmosphere and provide thicker coating for fasteners used in their products.
2. Manufacturers should try to coat bolts with yellow dichromate zinc.
3. Manufactured products going to the ultra-dry desert climate of Nevada and Arizona could use fasteners coated with clear chromate zinc provided they are at least 0.0003 thick
Adaptive Dijkstra’s Search Algorithm for MIMO detection
Employing Maximum Likelihood (ML) algorithm for signal detection in a large-scale Multiple-Input- Multiple-Output (MIMO) system with high modulation order is a computationally expensive approach. In this paper an adaptive best first search detection algorithm is proposed. The proposed Adaptive Dijkstra’s Search (ADS) algorithm exploits the resources available in the search procedure to reduce the required number of nodes to be visited in the tree. A tunable parameter is used to control the number of the best possible candidate nodes required. Unlike the conventional DS, the ADS algorithm results in signal detection with low computation complexity and quasi-optimal performance for systems under low and medium SNR regimes. Simulation results demonstrate a 25% computational complexity reduction, compared to the conventional DS
Optical Stark Effect and Dressed Excitonic States in a Mn-doped Quantum Dot
We report on the observation of spin dependent optically dressed states and
optical Stark effect on an individual Mn spin in a semiconductor quantum dot.
The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped
quantum dot are optically dressed by a strong laser field and the resulting
spectral signature is measured in photoluminescence. We demonstrate that the
energy of any spin state of a Mn atom can be independently tuned using the
optical Stark effect induced by a control laser. High resolution spectroscopy
reveals a power, polarization and detuning dependent Autler-Townes splitting of
each optical transition of the Mn-doped quantum dot. This experiment
demonstrates a complete optical resonant control of the exciton-Mn system
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