共查询到20条相似文献,搜索用时 15 毫秒
1.
Dutt MV Cheng J Li B Xu X Li X Berman PR Steel DG Bracker AS Gammon D Economou SE Liu RB Sham LJ 《Physical review letters》2005,94(22):227403
We report on the coherent optical excitation of electron spin polarization in the ground state of charged GaAs quantum dots via an intermediate charged exciton (trion) state. Coherent optical fields are used for the creation and detection of the Raman spin coherence between the spin ground states of the charged quantum dot. The measured spin decoherence time, which is likely limited by the nature of the spin ensemble, approaches 10 ns at zero field. We also show that the Raman spin coherence in the quantum beats is caused not only by the usual stimulated Raman interaction but also by simultaneous spontaneous radiative decay of either excited trion state to a coherent combination of the two spin states. 相似文献
2.
L. G. Si W. X. Yang X. Y. Lü J. H. Li X. X. Yang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):161-166
The authors show the formation of slow temporal vector
optical solitons in a cold lifetime-broadened four-level inverted-Y
atomic system. We demonstrate that Maxwell’s equations for
describing two orthogonally polarised components of a low intensity
signal field can evolve into two coupled nonlinear Schr?dinger
equations, which results in various distortion-free temporal vector
optical solitons, such as bright-bright or dark-dark vector
solitons. These results are produced from the correct balance
between dispersion, self- and cross-phase modulation (SPM and XPM)
effects. We also show that the integrable Manakov model can be
realised by adjusting the corresponding SPM, XPM and dispersion
effects of this inverted-Y atomic system. 相似文献
3.
The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects. 相似文献
4.
Coherent Zeeman resonance from electron spin coherence is demonstrated in a Lambda-type three-level system, coupling electron spin states via trions. The optical control of electron density that is characteristic of a mixed-type quantum-well facilitates the study of trion formation as well as the effects of many-body interactions on the manifestation of electron spin coherence in the nonlinear optical response. 相似文献
5.
Excitonic optical nonlinearities are exploited in room temperature InGaAsP multiple quantum wells to determine the in-well carrier mobilities and spin relaxation processes. The picosecond time scale of the spin relaxation leads to the creation of a fast all-optical polarisation switch by using a circular polarised excite and a linear polarised probe pulse. It is demonstrated that the operation of the switch is dependent on the sense of circular polarisation of the probe. An optically induced birefringence is identified. 相似文献
6.
7.
D.?Aumiler T.?Ban N.?Vuji?i? S.?Vdovi? H.?Skenderovi? G.?Pichler 《Applied physics. B, Lasers and optics》2009,97(3):553-560
We introduce a method for determination of the absolute frequencies of comb lines within an optical frequency comb spectrum.
The method utilizes the experimental and theoretical approach of the velocity-selective optical pumping of the atomic ground
state hyperfine levels induced by resonant pulse-train excitation. The information on the laser pulse repetition frequency
and carrier–envelope offset are physically mapped onto the 87Rb ground state hyperfine level population velocity distributions. Theoretical spectra are calculated using an iterative analytic
solution of the optical Bloch equations describing the resonant pulse-train excitation of four-level 87Rb atoms. They are employed to fit the measured spectra and obtain the parameters of the frequency comb, thus providing a
practical algorithm which can be used in real-time measurements. 相似文献
8.
We study nonlinear optical behaviors in pulse propagation through a medium consisting of four-level cascade-type cold atoms, where a radio-frequency (RF) field couples upper two-folded levels and double-dark resonances (DDRs) can arise. By numerically solving the coupled Bloch-Maxwell equations for atom and field simultaneously in space and time, we demonstrate dynamic control of light propagation and optical switching in such a four-level atomic medium. The proposed scheme may have potential applications in the design of optical switching and optical storage devices. 相似文献
9.
Sanvitto D Whittaker DM Shields AJ Simmons MY Ritchie DA Pepper M 《Physical review letters》2002,89(24):246805
The dynamics of the spin-triplet trion state, under high magnetic field in a GaAs/AlGaAs quantum well, are studied using time resolved spectroscopy. The oscillator strength of the triplet transition is shown to rise with increasing electron density, in good agreement with a theoretical model where the trion interacts with excess electrons in the quantum well. This analysis suggests that the spin-triplet trion state, which is expected to be an optically "dark" state, is experimentally observable due to the interactions with the excess electrons, demonstrating that X- cannot be regarded as an isolated three particle complex. 相似文献
10.
We consider the initialization of the spin state of a single electron trapped in a self-assembled quantum dot via optical pumping of a trion level. We show that with a magnetic field applied perpendicular to the growth direction of the dot, a near-unity fidelity can be obtained in a time equal to a few times the inverse of the spin-conserving trion relaxation rate. This method is several orders of magnitude faster than with the field aligned parallel, since this configuration must rely on a slow hole spin-flip mechanism. This increase in speed does result in a limit on the maximum obtainable fidelity, but we show that for InAs dots, the error is very small. 相似文献
11.
A state space model(SSM) is derived for quantum-dot semiconductor optical amplifiers(QD-SOAs).Rate equations of QD-SOA are formulated in the form of state update equations,where average occupation probabilities along QD-SOA cavity are considered as state variables of the system.Simulations show that SSM calculates QD-SOA's static and dynamic characteristics with high accuracy. 相似文献
12.
S. Laurent O. Krebs S. Cortez M. Senes X. Marie T. Amand P. Voisin J. -M. Grard 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):404
We report on optical orientation of electrons in n-doped InAs/GaAs quantum dots. Under non-resonant cw optical pumping, we measure a negative circular polarization of the luminescence of charged excitons (or trions) at low temperature (T=10 K). The dynamics of the recombination and of the circular polarization is studied by time-resolved spectroscopy. We discuss a simple theoretical model for the trion relaxation, that accounts for this remarkable polarization reversal. The interpretation relies on the bypass of Pauli blocking allowed by the anisotropic electron–hole exchange. Eventually, the spin relaxation time of doping electrons trapped in quantum dots is measured by a non-resonant pump–probe experiment. 相似文献
13.
《Physica E: Low-dimensional Systems and Nanostructures》2011,43(10):2493-2496
Coherent spin precession of electrons and excitons is observed in charge tunable InP quantum dots under the transverse magnetic field by means of time-resolved Kerr rotation. In a quantum dot doped by one electron, spin precession of the doped electron in the quantum dot starts out of phase with spin precession of the doped electrons in a GaAs substrate just after a trion is formed and persists for more than 2 ns even after the trion recombines. Simultaneously spin precession of a trion (hole) starts. Observation of spin precession of both a doped electron and a trion (hole) confirms creating coherent superposition of an electron and a trion as the initialization process of spin of doped electrons in quantum dots. In a neutral quantum dot, the exciton spin precession starts out of phase with spin precession of the doped electrons in a GaAs substrate and the precession frequency does not converge to 0 at the zero field limit. It contains the electron–hole exchange interaction and corresponds to the splitting between bright and dark excitons under the transverse magnetic field. 相似文献
14.
The coherent superposition of two-atomic levels induced by coherent population trapping is employed in the two-level system, the standard three-level Λ type scheme and the four-level N-type systems and a weak probe pulse scans across the system. A theoretical analysis about the response of medium to the probe field is given. It is shown that under different initial conditions, the coherent superposition of the dark state exhibits abundant optical phenomena response to the probe field. It can change the absorption or gain and the dispersion relationship in the medium experienced by the probe. In the embedded three-level scheme, the probe experiences a crossover from absorption to transparent and then to amplification. Consequently the group velocity of the probe pulse can be controlled to propagate either as a subluminal, a standard, a superluminal or even a negative speed. In the embedded four-level N-type system, it can give an enhancement to the Giant Kerr effect and overcome the limitation of two-photon absorption, then make the nonlinear properties of the medium richer than the traditional N-type scheme. 相似文献
15.
Korenev VL 《Physical review letters》2007,99(25):256405
Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins-the nuclear spin nanomagnet. 相似文献
16.
Ping Li Qingpu Wang Xingyu Zhang Yurong Wang Shichen Li He Jingliang Lu Xingqiang 《Optics & Laser Technology》2001,33(6)
A diode-pumped Nd:YVO4 laser passively Q switched with GaAs is studied theoretically and experimentally. We have demonstrated the influence of single-photon absorption, two-photon absorption and free-carrier absorption in GaAs on the Q-switched pulse characteristics. The pulse profile, pulse energy and pulse width of the Q switching with GaAs are simulated by using the conventional rate equations of the four-level laser system. The experimental results show reasonable agreement with the theoretical results on the whole. 相似文献
17.
准Λ型4能级系统具有电磁诱导吸收(EIA)和电磁诱导透明(EIT)两种特性.准Λ型4能级系统包括两个基态精细结构能级和两个激发态精细结构能级,除光学耦合场和探测场外,附加了一个射频场作用于两个激发态精细结构能级之间.若对此系统进行拓展,在两个基态精细结构能级之间引入一个驱动场,则构成4场作用下的闭合Λ型4能级系统.本文对新引进的驱动场的作用规律进行了重点研究.研究结果表明,当驱动场和射频场的Rabi频率满足不同关系时,系统呈现EIA或EIT两种不同特性,探测吸收曲线的整体轮廓也随之改变. 相似文献
18.
K. I. Osman S. S. Hassan A. Joshi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(1):119-130
The effects of spontaneously generated coherence (SGC) and phases of
optical fields on the phenomenon of electromagnetically induced
transparency (EIT) are investigated in a four-level inverted-Y
system and in a five-level K-type system under various parametric
conditions in order to demonstrate controllability of the EIT,
dispersion properties, and group velocity in such systems. Non-zero
second-order susceptibility in both systems is due to the SGC
effect. The experimental viability of the model in semiconductor
quantum well systems is also discussed. 相似文献
19.
A system of equations is formulated describing the evolution of a slowly varying envelope of an arbitrarily polarized ultrashort pulse of electromagnetic radiation in a medium with its resonant properties determined by an ensemble of isolated quantum dots. It is assumed that the concentration of quantum dots is small and that the whole system is equivalent to a gas of resonant four-level atoms. Particular solutions are found that correspond to the propagation of a stationary optical pulse. It is shown by numerical solution of the generalized truncated Maxwell-Bloch equations that steady-state propagation is possible only for circularly polarized light pulses, whereas the pulses of arbitrary polarization either decay and experience the dispersion-related broadening or are converted into circularly polarized solitary waves. 相似文献