Stimulated emission from the biexciton in a single self-assembled II-VI quantum dot

Using two-photon excitation, stimulated emission from the biexciton state in a single CdSe/ZnSe quantum dot is observed in a two-pulse configuration. We directly time resolve the emission-absorption characteristics and verify the potential for laser action. By setting the polarization of the stimulation pulse, the recombination path of the biexciton and, by this, the state of the photons emitted in the decay cascade is controlled. We elaborate also the coherent response and address entanglement and disentanglement of the exciton-biexciton system.     

Two-color two-photon Rabi oscillation of biexciton in single InAs/GaAs quantum dot

A two-photon absorption resonance is observed when the sum-frequency of two laser pulses equals the creation energy of a biexciton in a single InAs/GaAs semiconductor quantum dot. Resonant excitation of the two-color two-photon transition results in a coherent oscillation that is remarkably similar to a single-color two-photon Rabi oscillation of the crystal-ground to biexciton optical transition. A model explaining the coherent two-photon absorption is presented.     

Stable biexcitonic lasing of CuCl quantum dots under two-photon resonant excitation

We have observed ultraviolet lasing of CuCl quantum dots embedded in a NaCl single crystalline matrix. Stable ultraviolet lasing of biexciton (two e–h pairs) luminescence has been achieved below 70 K under the two-photon direct excitation of biexcitons of CuCl quantum dots. Laser action occurs with parallely cleaved surfaces of the NaCl crystalline matrix acting as an optical cavity, which shows a very high efficiency of lasing.     

Biexciton quantum coherence in a single quantum dot

Nondegenerate (two-wavelength) two-photon absorption using coherent optical fields is used to show that there are two different quantum mechanical pathways leading to formation of the biexciton in a single quantum dot. Of specific importance to quantum information applications is the resulting coherent dynamics between the ground state and the biexciton from the pathway involving only optically induced exciton/biexciton quantum coherence. The data provide a direct measure of the biexciton decoherence rate which is equivalent to the decoherence of the Bell state in this system, as well as other critical optical parameters.     

Correlated photon-pair emission from pulse-pumped quantum dots embedded in a microcavity

We theoretically investigate the optical response of a quantum dot, embedded in a microcavity and incoherently excited by pulsed pumping. The exciton and biexciton transitions are off-resonantly coupled with the left- and right-polarized mode of the cavity, while the two-photon resonance condition is fulfilled. Rich behaviors are shown to occur in the time dependence of the second-order correlation functions which refer to counter-polarized photons. The system’s dynamics turns out to be much faster than typical experimental detection times. The experimentally accessible time-averaged quantities confirm that such a dot-cavity system behaves as a good emitter of single polarization-correlated photon pairs.     

Bipolariton laser emission from a GaAs microcavity

Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser-like behavior. Very small linewidths were measured, lying below 110 μeV and 150 μeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Varying the pump laser polarization, we were able to show the selection rules for the biexciton particle creation in the quantum well. Simultaneous photoluminescence and near-field measurements show that the polariton and bipolariton emission are spectrally and spatially separated.     

Two-photon coherent control of a single quantum dot

We report on two-photon coherent control of the biexciton state in single Stranski-Krastanov CdSe quantum dots. Clear interference patterns are observed at twice the optical frequency. The decay of the interference contrast is nonexponential and caused by a dynamical inhomogeneous broadening of the energy levels due to long-term fluctuations in the dot environment.     

Two-photon excitation of confined biexcitons in CuCl quantum dots

We have studied direct creation processes of confined biexcitons in CuCl quantum dots by polarization-dependent resonant two-photon excitation spectroscopy. The two-photon absorption band for the lowest state of the biexciton (total angular momentum J=0) which appears on the lower energy side of confined exciton band was identified from the analysis of the polarization dependence of the photoluminescence excitation spectrum of the biexciton. Furthermore, the two-photon excitation process for the excited state of the biexciton (J=2) was also found with polarization dependence different from the J=0 biexciton state.     

Correlated photons from multi-carrier complexes in GaAs quantum dots

We have studied micro-photoluminescence spectra of a self-assembled single GaAs quantum dot under 8 K. With strong pulsed excitation, the micro-photoluminescence spectrum shows bright emission lines originated from an exciton, a positively charged exciton, and a biexciton, together with weak lower energy emissions reflecting multi-excitonic structures with more carriers. We have identified the origins of these weak emission lines, and showed the existence of charged biexciton states, through single photon correlation measurements and excitation power dependence of the photoluminescence intensity. In addition, investigating the radiative recombination process of the charged biexciton, we have determined the electron–hole exchange energy in the GaAs quantum dot.     

Coherent control in a single semiconductor quantum dot exhibiting excitonic and biexcitonic features

We have developed a simplified theoretical model to analyze the phenomenon of coherent control in a single semiconductor quantum dot excited by a pair of optical pulses. The first pulse populates a biexciton state by two-photon absorption while the second pulse generates population in the exciton state via deexcitation from the biexciton state. We have used density-matrix analysis for a 3-level system to calculate the time dependent biexciton and exciton state populations. The usual 9×9 matrix has been reduced to a 6×6 matrix. The time variation of the population in each state and it’s dependence on the pulse delay manifest coherent control. Numerical estimates made for In_0.5Ga_0.5As/GaAs single quantum dots qualitatively agree with the recent experimental results. PACS 78.67.Hc; 42.50.Md; 78.55.Cr     

Room-temperature ordered photon emission from multiexciton states in single CdSe core-shell nanocrystals

We report room-temperature ordered multiphoton emission from multiexciton states of single CdSe(CdZnS) core(-shell) colloidal nanocrystals (NCs) that are synthesized by wet chemical methods. Spectrally and temporally resolved measurements of biexciton and triexciton emission from single NCs are also presented. A simple four level system models the results accurately and provides estimates for biexciton and triexciton radiative lifetimes and quantum yields.     

非简并双光子微脉塞的发射几率

将简并双光子微脉塞的量子理论推广到非简并情形, 给出了原子发射几率的解析表达式并且分析了相应的性质.发现由于在微脉塞中存在两种腔场模式,导致有两个自由度来改变原子在经过腔场时所受到的势场,因此非简并双光子微脉塞的发射几率的行为不同于简并双光子情况下的发射几率.     

Effects of Dipole Interaction on Emission Spectra of Atoms in Two-Photon Processes

We study the interaction of a pair of coupling two-level atoms with a single mode of the radiation field in an ideal cavity via two-photon resonant transition and/or degenerate Ramancoupled processes.In particular, we consider the emission spectra for both two-photon processes. The effects of atomic coupling are analyzed and the properties of emission spectra for large photon number of the cavity-mode are discussed.     

Single-mode spontaneous emission from a single quantum dot in a three-dimensional microcavity

The spontaneous emission from an isolated semiconductor quantum dot state has been coupled with high efficiency to a single, polarization-degenerate cavity mode. The InAs quantum dot is epitaxially formed and embedded in a planar epitaxial microcavity, which is processed into a post of submicron diameter. The single quantum dot spontaneous emission lifetime is reduced from the noncavity value of 1.3 ns to 280 ps, resulting in a single-mode spontaneous emission coupling efficiency of 78%.     

Single-dot spectroscopy in high magnetic fields

We report on photoluminescence measurements from a single InAs/GaAs quantum dot in magnetic fields up to 28 T. Mesa-patterned structure has been used to limit the number of investigated dots. Three pairs of Zeeman-split emission lines with the same effective g*-factor and diamagnetic shift have been observed. The attribution of the lines to recombination of a neutral exciton, a biexciton, and a charged exciton is discussed.     

Exciton and multi-exciton structures in GaAs quantum dots studied by single-photon correlation spectroscopy

Single-photon emitters and detectors are key devices for realizing secure communications by single-photon-based cryptography and single-photon-based quantum computing. For the establishment of these technologies, we need to understand the electronic structures of single and multiple excitons. Therefore, we have studied their emissions via the micro-photoluminescence (μ-PL) spectra of strain-free GaAs/AlGaAs single quantum dots, using excitation power dependence, time-resolved, and single-photon correlation measurements. Under pulsed excitation, we observed clear photon antibunching and bunching by auto- and cross-correlation measurements. From these results, we found that the emission peaks observed in the μ-PL spectra originated from exciton, charged exciton, and biexciton states.     

Photoluminescence of single quantum wires and quantum dots

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.     

Polariton-biexciton transitions in a semiconductor microcavity

The influence of four-particle correlations on the nonlinear optics of a semiconductor microcavity is determined by a pump-and-probe investigation. Experiments are performed on a nonmonolithic microcavity which contains a ZnSe quantum well. In this system the biexciton binding energy exceeds both the normal-mode splitting between exciton and cavity mode and all damping constants. Oscillatory spectral features below the excitonic resonance are observed in the response for counterpolarized beams. Comparison with model calculations shows that in this case the coherent nonlinearity is dominated by biexciton-exciton interactions beyond the Hartree-Fock approximation.     

Optical study of single InAs on In0.12Ga0.88As self-assembled quantum dots: biexciton binding energy dependence on the dots size

Single self-assembled InAs quantum dots embedded in a In_0.12Ga_0.88As quantum well and emitting in the near infrared have been optically investigated. The dependence on the excitation power of the single quantum dot photoluminescence has been used to identify the emission of the biexciton complex. The biexciton binding energy, which has been measured for a dozen dots, increases with increasing exciton transition energy for the dot sizes investigated in the present work, as a consequence of stronger confinement in a smaller quantum dot. The obtained data is compared with experimental results available in the literature for InAs quantum dots. PACS 78.67.Hc; 73.21.La; 78.55.Cr     

Photon antibunching from a single quantum-dot-microcavity system in the strong coupling regime

We observe antibunching in the photons emitted from a strongly coupled single quantum dot and pillar microcavity in resonance. When the quantum dot was spectrally detuned from the cavity mode, the cavity emission remained antibunched, and also anticorrelated from the quantum dot emission. Resonant pumping of the selected quantum dot via an excited state enabled these observations by eliminating the background emitters that are usually coupled to the cavity. This device demonstrates an on-demand single-photon source operating in the strong coupling regime, with a Purcell factor of 61+/-7 and quantum efficiency of 97%.