共查询到20条相似文献,搜索用时 31 毫秒
1.
Takasu Y Saito Y Takahashi Y Borkowski M Ciuryło R Julienne PS 《Physical review letters》2012,108(17):173002
We report the successful production of subradiant states of a two-atom system in a three-dimensional optical lattice starting from doubly occupied sites in a Mott insulator phase of a quantum gas of atomic ytterbium. We can selectively produce either a subradiant 1(g) state or a superradiant 0(u) state by choosing the excitation laser frequency. The inherent weak excitation rate for the subradiant 1(g) state is overcome by the increased atomic density due to the tight confinement in a three-dimensional optical lattice. Our experimental measurements of binding energies, linewidth, and Zeeman shift confirm the observation of subradiant levels of the 1(g) state of the Yb(2) molecule. 相似文献
2.
T. V. Shahbazyan V. N. Pustovit 《Applied Physics A: Materials Science & Processing》2011,103(3):755-758
We study cooperative emission by an ensemble of emitters, such as fluorescing molecules or semiconductor quantum dots, near
a metal nanoparticle. The primary mechanism of cooperative emission is resonant energy transfer between emitters and plasmons
rather than Dicke radiative coupling between emitters. The emission is dominated by three superradiant states with the same
quantum yield as a single emitter, leading to a drastic reduction of ensemble radiated energy down to just thrice of that
by a single emitter, the remaining energy being dissipated in the metal through subradiant states. We perform numerical calculations
of system eigenstates and find that the plasmonic Dicke effect interactions affect is not impacted by the interactions between
emitters or non-radiative losses in the metal. 相似文献
3.
We investigate nonequilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel nonequilibrium tunneling processes involving high-spin states, which cannot be excited from the ground state because of spin blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots. 相似文献
4.
Simon CM Belhadj T Chatel B Amand T Renucci P Lemaitre A Krebs O Dalgarno PA Warburton RJ Marie X Urbaszek B 《Physical review letters》2011,106(16):166801
The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance. This observation in photoluminescence experiments is made possible by introducing a novel optical detection scheme for the resonant electron hole pair (exciton) generation. 相似文献
5.
V. P. Kochereshko V. N. Kats A. V. Platonov R. A. Suris G. E. Cirlin A. D. Buravlev Yu. B. Samsonenko L. Besombes C. Le Gal H. Mariette 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(5):722-725
The results of a study into the photoluminescence spectra of a set of quantum dots based on GaAs enclosed in AlGaAs nanowires are presented. The steady state and time resolved spectra of photoluminescence under optical excitation both from an array of quantum wires/dots and a single quantum wire/dot have been measured. In the photoluminescence spectra of single quantum dots, emission lines of excitons, biexcitons and tritons have been found. The binding energy of the biexciton in the studied structures was deduced to be 8 meV. 相似文献
6.
Vidar Gudmundsson Nzar Rauf Abdullah Chi‐Shung Tang Andrei Manolescu Valeriu Moldoveanu 《Annalen der Physik》2019,531(11)
It is shown that quantum electromagnetic transitions to high orders are essential to describe the time‐dependent path of a nanoscale electron system in a Coulomb blockade regime when coupled to external leads and placed in a 3D rectangular photon cavity. The electronic system consists of two quantum dots embedded asymmetrically in a short quantum wire. The two lowest in energy spin degenerate electron states are mostly localized in each dot with only a tiny probability in the other dot. In the presence of the leads, a slow high‐order transition between the ground states of the two quantum dots is identified. The Fourier power spectrum for photon–photon correlations in the steady state shows a Fano type of resonance for the frequency of the slow transition. Full account is taken of the geometry of the multilevel electronic system, and the electron–electron Coulomb interactions together with the para‐ and diamagnetic electron–photon interactions are treated with step‐wise exact numerical diagonalization and truncation of appropriate many‐body Fock spaces. The matrix elements for all interactions are computed analytically or numerically exactly. 相似文献
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8.
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
9.
Morgan E. Ware Allan S. Bracker Eric Stinaff Daniel Gammon David Gershoni Vladimir L. Korenev 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):55
Using polarization-sensitive photoluminescence and photoluminescence excitation spectroscopy, we study single InAs/GaAs self-assembled quantum dots. The dots were embedded in an n-type, Schottky diode structure allowing for control of the charge state. We present here the exciton, singly charged exciton (positive and negative trions), and the twice negatively charged exciton. For non-resonant excitation below the wetting layer, we observed a large degree of polarization memory from the radiative recombination of both the positive and negative trions. In excitation spectra, through the p-shell, we have found several sharp resonances in the emission from the s-shell recombination of the dot in all charged states. Some of these excitation resonances exhibit strong coulomb shifts upon addition of charges into the quantum dot. One particular resonance of the negatively charged trion was found to exhibit a fine structure doublet under circular polarization. This observation is explained in terms of resonant absorption into the triplet states of the negative trion. 相似文献
10.
We study a four-electron system in a vertically coupled four-layer quantum
dot under a magnetic field by the exact diagonalization of the Hamiltonian
matrix. We find that discontinuous ground-state energy transitions are induced by an external magnetic field. We find that dot-dot distance and
electron-electron interaction strongly affect the low-lying states of the
coupled quantum dots. The inter-dot correlation leads to some sequences of
possible disappearances of ground state transitions, which are present for
uncoupled dots. 相似文献
11.
WANG An-Mei XIE Wen-Fang 《理论物理通讯》2005,44(7)
We study a four-electron system in a vertically coupled four-layer quantum dot under a magnetic field by the exact diagonalization of the Hamiltonian matrix. We find that discontinuous ground-state energy transitions are induced by an external magnetic field. We find that dot-dot distance and electron-electron interaction strongly affect the low-lying states of the coupled quantum dots. The inter-dot correlation leads to some sequences of possible disappearances of ground state transitions, which are present for uncoupled dots. 相似文献
12.
We investigate quantum dot arrays and their application to quantum computation. The arrays analyzed contain a total of a few operating electrons with constant tunneling between the dots. We construct quantum two-level systems near the ground state with a large energy separation to the remainder of the states and with the electrostatic interaction modeled within the capacitance matrix formalism. A set of representative examples is investigated numerically. 相似文献
13.
Ware ME Stinaff EA Gammon D Doty MF Bracker AS Gershoni D Korenev VL Bădescu SC Lyanda-Geller Y Reinecke TL 《Physical review letters》2005,95(17):177403
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions. 相似文献
14.
B. Ilahi L. Sfaxi F. Hassen H. Maaref B. Salem G. Guillot A. Jbeli X. Marie 《Applied Physics A: Materials Science & Processing》2005,81(4):813-816
Room temperature 1.3 μm emitting InAs quantum dots (QDs) covered by an In0.4Ga0.6As/GaAs strain reducing layer (SRL) have been fabricated by solid source molecular beam epitaxy (SSMBE) using the Stranski–Krastanov growth mode. The sample used has been investigated by temperature and excitation power dependent photoluminescence (PL), photoluminescence excitation (PLE), and time resolved photoluminescence (TRPL) experiments. Three emission peaks are apparent in the low temperature PL spectrum. We have found, through PLE measurement, a single quantum dot ground state and the corresponding first excited state with relatively large energy spacing. This attribute has been confirmed by TRPL measurements which allow comparison of the dynamics of the ground state with that of the excited states. Optical transitions related to the InGaAs quantum well have been also identified. Over the whole temperature range, the PL intensity is found to exhibit an anomalous increase with increasing temperatures up to 100 K and then followed by a drop by three orders of magnitude. Carrier’s activation energy out of the quantum dots is found to be close to the energy difference between each two subsequent transition energies. PACS 68.65.Ac; 68.65.Hb; 78.67.Hc 相似文献
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16.
Jia-Ren Lee Chien-Rong Lu Wei-I Lee Shih-Chang Lee 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):562-568
We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state. 相似文献
17.
利用密度泛函理论在B3LYP/6-31G(d)基组水平上研究了具有zigzag边界的石墨烯量子点,结果表明不同大小的石墨烯量子点的基态都是具有磁性的自旋三重态.其磁性一方面来源于zigzag边界上占有凸出位置的碳原子,另一方面来源于带有孤对电子的碳原子.从整体上看,除6b结构外,其他结构的能隙随着苯环数量的增加逐渐减小,而附加电荷却使体系能隙明显减小.用含时密度泛函理论(TD-DFT)对能隙为3.83 eV的由六个苯环排列成的三角形结构进行了激发态的计算,发现第十七激发态强度最大,能量为3.93 eV,对
关键词:
石墨烯量子点
磁性
能隙
激发态 相似文献
18.
T. Prosen D. L. Shepelyansky 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(4):515-518
We establish analogy between a microwave ionization of Rydberg
atoms and a charge transport through a chaotic quantum dot
induced by a monochromatic field in a regime with a potential
barrier between dot contacts.
We show that the quantum coherence leads to dynamical localization
of electron excitation in energy
so that only a finite number of photons is absorbed inside the dot.
The theory developed determines the dependence of localization length
on dot and microwave parameters showing that the microwave power
can switch the dot between metallic and insulating regimes.
ultiphoton ionization and excitation to highly excited states
(e.g., Rydberg states) 相似文献
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20.
The optical properties of the populated ZnCdSe/ZnSe quantum dots have been studied by photoluminescence spectra measured with different laser excitation apertures at temperatures from 22 to 300 K. The differences of spectral features between small and large excitation spot suggest the existence of quantum dot size fluctuation in the system. The temperature evolution of photoluminescence spectral features revealed that two types of quantum dots with different densities and sizes coexist in ZnCdSe/ZnSe system. The energy spacings of the two kinds of quantum dot emissions are about 50 meV at various temperatures. The thermally activated lateral transfer processes of carriers populated in the two sorts of quantum dots are investigated by temperature dependences of spectral intensities. 相似文献