Showing papers on "Spontaneous emission published in 2004"
TL;DR: The observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity, may provide a basis for future applications in quantum information processing or schemes for coherent control.
Abstract: Cavity quantum electrodynamics, a central research field in optics and solid-state physics, addresses properties of atom-like emitters in cavities and can be divided into a weak and a strong coupling regime. For weak coupling, the spontaneous emission can be enhanced or reduced compared with its vacuum level by tuning discrete cavity modes in and out of resonance with the emitter. However, the most striking change of emission properties occurs when the conditions for strong coupling are fulfilled. In this case there is a change from the usual irreversible spontaneous emission to a reversible exchange of energy between the emitter and the cavity mode. This coherent coupling may provide a basis for future applications in quantum information processing or schemes for coherent control. Until now, strong coupling of individual two-level systems has been observed only for atoms in large cavities. Here we report the observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of about 140 microeV.
1,809 citations
TL;DR: It is shown that under the influence of pure vacuum noise two entangled qubits become completely disentangled in a finite-time, and in a specific example the time to be given by ln((2+sqrt[2] / 2) times the usual spontaneous lifetime).
Abstract: We show that under the influence of pure vacuum noise two entangled qubits become completely disentangled in a finite-time, and in a specific example we find the time to be given by ln((2+sqrt[2] / 2) times the usual spontaneous lifetime.
1,487 citations
TL;DR: The results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
Abstract: Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP–QW coupling. Large enhancements of the internal quantum efficiencies (etaint) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
1,349 citations
TL;DR: In this paper, the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal, and both inhibited and enhanced decay rates are observed depending on the optical emission frequency.
Abstract: Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.
1,046 citations
Journal Article•
TL;DR: This work shows that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal, providing a basis for all-solid-state dynamic control of optical quantum systems.
Abstract: Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.
1,019 citations
TL;DR: The experimental demonstration of an electrically driven, single-mode, low threshold current (∼260 μA) photonic band gap laser operating at room temperature is reported, a small step toward a thresholdless laser or a single photon source.
Abstract: We report the experimental demonstration of an electrically driven, single-mode, low threshold current (∼260 μA) photonic band gap laser operating at room temperature. The electrical current pulse is injected through a sub-micrometer-sized semiconductor wire at the center of the mode with minimal degradation of the quality factor. The actual mode of interest operates in a nondegenerate monopole mode, as evidenced through the comparison of the measurement with the computation based on the actual fabricated structural parameters. As a small step toward a thresholdless laser or a single photon source, this wavelength-size photonic crystal laser may be of interest to photonic crystals, cavity quantum electrodynamics, and quantum information communities.
831 citations
TL;DR: The theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures.
Abstract: As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size1,2. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies—for example, displays, fluorescence tagging3, solid-state lighting and lasers4. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron–hole pairs (the electron–hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.
544 citations
16 May 2004
TL;DR: In this paper, 3D photonic crystals with light-emitters and point-defects are fabricated and investigated, and it is experimentally shown that light emission is suppressed at the complete crystal parts, while cavity modes are successfully observed at the defect parts.
Abstract: 3D photonic crystals with light-emitters and point-defects are fabricated and investigated. It is experimentally shown that light-emission is suppressed at the complete crystal parts, while cavity modes are successfully observed at the defect parts.
341 citations
Proceedings Article•
01 Jan 2004
TL;DR: Three-dimensional photonic crystals containing artificial point defects have been fabricated to emit light at optical communications wavelengths by stacking 0.7-micrometer-period gallium arsenide striped layers resulting in a 3D “woodpile” photonic crystal.
325 citations
TL;DR: C cavity cooling of single rubidium atoms stored in an intracavity dipole trap is demonstrated and it is estimated that the observed cooling rate is at least five times larger than that produced by free-space cooling methods, for comparable excitation of the atom.
Abstract: All conventional methods to laser-cool atoms rely on repeated cycles of optical pumping and spontaneous emission of a photon by the atom. Spontaneous emission in a random direction provides the dissipative mechanism required to remove entropy from the atom. However, alternative cooling methods have been proposed for a single atom strongly coupled to a high-finesse cavity; the role of spontaneous emission is replaced by the escape of a photon from the cavity. Application of such cooling schemes would improve the performance of atom-cavity systems for quantum information processing. Furthermore, as cavity cooling does not rely on spontaneous emission, it can be applied to systems that cannot be laser-cooled by conventional methods; these include molecules (which do not have a closed transition) and collective excitations of Bose condensates, which are destroyed by randomly directed recoil kicks. Here we demonstrate cavity cooling of single rubidium atoms stored in an intracavity dipole trap. The cooling mechanism results in extended storage times and improved localization of atoms. We estimate that the observed cooling rate is at least five times larger than that produced by free-space cooling methods, for comparable excitation of the atom.
298 citations
TL;DR: The results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments.
Abstract: We present a simple method to measure the radiative and nonradiative recombination rates of individual fluorescent emitters at room temperature. By placing a single molecule successively close and far from a dielectric interface and simultaneously measuring its photoluminescence decay and its orientation, both the radiative and nonradiative recombination rates can be determined. For CdSe nanocrystals, our results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments. The bidimensional nature of the transition dipole is also directly evidenced from a single-particle measurement.
TL;DR: A parallel configuration of two interacting whispering-gallery-mode optical resonators is theoretically studied and a narrowband modal structure is shown as a basis for a widely tunable delay line.
Abstract: We theoretically study a parallel configuration of two interacting whispering-gallery-mode optical resonators and show a narrowband modal structure as a basis for a widely tunable delay line. For the optimum coupling configuration the system can possess an unusually narrow spectral feature with a much narrower bandwidth than the loaded bandwidth of each individual resonator. The effect has a direct analogy with the phenomenon of electromagnetically induced transparency in quantum systems for which the interference of spontaneous emission results in ultranarrow resonances.
TL;DR: In this paper, the spontaneous emission of a single molecule is substantially modified close to a metallic nanostructure, and the spectral behavior of the radiative and nonradiative decay rates and of the local field factor in the vicinity of a plasmon resonance is studied.
Abstract: The spontaneous emission of a single molecule is substantially modified close to a metallic nanostructure. We study the spectral behavior of the radiative and nonradiative decay rates and of the local-field factor in the vicinity of a plasmon resonance. We show that the highest fluorescence enhancement is obtained for an emission wavelength redshifted from the plasmon resonance, and that quenching always dominates at plasmon resonance. These results may have experimental implications in spectroscopy and monitoring of elementary light sources.
TL;DR: In this paper, the radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination was calculated for solar cells with lateral fluctuations of the band-gap energy, and a simple analytical model quantified the fluctuations by the standard deviation σEg from the mean band gap.
Abstract: The radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination is calculated for solar cells with lateral fluctuations of the band-gap energy. A simple analytical model quantifies the fluctuations by the standard deviation σEg from the mean band gap. The calculated maximum efficiency decreases by 1.7% (absolute) for σEg=50 meV and by 6.1% for σEg=100 meV with respect to a uniform band gap.
TL;DR: In this article, the photoluminescence intensity of the {112¯2} QW is the strongest among the three QWs, and the internal quantum efficiency was estimated to be as large as about 40% at room temperature.
Abstract: InxGa1−xN multiple quantum wells (QWs) with [0001], ⟨112¯2⟩, and ⟨112¯0⟩ orientations have been fabricated by means of the regrowth technique on patterned GaN template with striped geometry, normal planes of which are (0001) and {112¯0}, on sapphire substrates. It was found that photoluminescence intensity of the {112¯2} QW is the strongest among the three QWs, and the internal quantum efficiency of the {112¯2} QW was estimated to be as large as about 40% at room temperature. The radiative recombination lifetime of the {112¯2} QW was about 0.38ns at low temperature, which was 3.8 times shorter than that of conventional [0001]-oriented InxGa1−xN QWs emitting at a similar wavelength of about 400nm. These findings strongly suggest the achievement of stronger oscillator strength owing to the suppression of piezoelectric fields.
TL;DR: In this paper, the authors measured the spectrum and efficiency of infrared light emission from ambipolar carbon nanotube field effect transistors (FET transistors) and found that the spectral and energy efficiency of radiative recombination is between 10-6 and 10-7 photons/electron−hole pair, and the possible quenching mechanisms are discussed.
Abstract: We measure the spectrum and efficiency of the infrared light emission from ambipolar carbon nanotube field-effect transistors. The width of the emission peak is strongly device-structure dependent. Long devices (∼50 μm) show narrow spectral peaks that we attribute to relaxed carrier recombination, while short devices (∼500 nm) show broad peaks due to hot carrier recombination. The hot carrier distribution is limited to energies below the energies of the optical/zone boundary phonons near 180 meV. The efficiency of the radiative recombination is between 10-6 and 10-7 photons/electron−hole pair, and the possible quenching mechanisms are discussed.
TL;DR: In this paper, the authors analyze the influence of the microstructure and temperature on the coherence properties and show how to engineer thermoradiative properties of surfaces and report the design of a quasi-isotropic source and a very directional source of thermal light.
Abstract: The emission of light by a material at temperature T has been shown recently to be coherent in the near field These properties were attributed to the thermal excitation of surface polaritons We review the origin of this phenomenon We analyze the influence of the microstructure and temperature on the coherence properties and show how to engineer thermoradiative properties of surfaces We report the design of a quasi-isotropic source and a very directional source of thermal light We also report a measurement of the transverse coherence length of a thermal source of light
TL;DR: In this paper, the radiative recombination in the graded base layer of InGaP/GaAs heterojunction bipolar transistors (HBTs) has been observed for a 1 μm×16 μm emitter HBT.
Abstract: This letter reports the direct observation of the radiative recombination in the graded base layer of InGaP/GaAs heterojunction bipolar transistors (HBTs). For a 1 μm×16 μm emitter HBT, we demonstrate the change of the spontaneous light emission intensity (ΔIout) as the base current (Δib) of the HBT is varied from 0 to 5 mA, i.e., an HBT operating as a light-emitting transistor. We also demonstrate output light modulation from the base layer at 1 MHz with the base current modulated at 1 MHz in normal transistor mode operation of the HBT.
TL;DR: In this paper, the authors have presented a study supported in part by the Basque Departamento de Educación, Universidades e Investigació, and the University of the Balque Country UPV/EHU (Contract No. 00206.215-13639/2001).
Abstract: This work has been supported in part by the Basque Departamento de Educacion, Universidades e Investigacion, the University of the Basque Country UPV/EHU (Contract No. 00206.215-13639/2001) and the Spanish Ministerio de Ciencia y Tecnologia (Contract No. MAT2001-0946).
TL;DR: It is demonstrated that quantum dots provide a model system for testing theories on the influence of local-field effects on the spontaneous emission rate and the experimentally observed influence of n on the radiative lifetime is smaller than predicted by well-known models for local- field corrections but in good agreement with a recently developed fully microscopic model.
Abstract: The refractive index dependence of the spontaneous emission rate is determined using organically capped CdSe and CdTe quantum dots as probes. The radiative lifetime of the exciton emission is measured in a variety of apolar solvents with refractive indices n between 1.37 and 1.50. It is demonstrated that quantum dots provide a model system for testing theories on the influence of local-field effects on the spontaneous emission rate. The experimentally observed influence of n on the radiative lifetime is smaller than predicted by well-known models for local-field corrections but is in good agreement with a recently developed fully microscopic model for the local-field enhancement of the spontaneous emission rate.
TL;DR: In this article, the spontaneous decay rate of an excited atom placed near a dielectric cylinder is investigated, and the main contribution to decay rates is due to the quasistatic interaction of the atom dipole momentum with the nanofiber.
Abstract: The spontaneous decay rate of an excited atom placed near a dielectric cylinder is investigated. Special attention is paid to the case when the cylinder radius is small in comparison with radiation wavelength (nanofiber or photonic wire). In this case, the analytical expressions of the transition rates for different orientations of a dipole are derived. It is shown that the main contribution to decay rates is due to the quasistatic interaction of the atom dipole momentum with the nanofiber, and the contributions of guided modes are exponentially small. On the contrary, in the case when the radius of the fiber is only slightly less than the radiation wavelength, the influence of guided modes can be substantial. The results obtained are compared with the case of a dielectric nanospheroid and an ideally conducting wire.
TL;DR: In this paper, the authors reported enhanced radiative recombination realized by incorporating InGaAs quantum wells in the base layer of light-emitting InGaP/GaAs heterojunction bipolar transistors (LETs) operating in the common-emitter configuration.
Abstract: This letter reports the enhanced radiative recombination realized by incorporating InGaAs quantum wells in the base layer of light-emitting InGaP/GaAs heterojunction bipolar transistors (LETs) operating in the common-emitter configuration. Two 50 A In1−xGaxAs (x=85%) quantum wells (QWs) acting, in effect, as electron capture centers (“traps”) are imbedded in the 300 A GaAs base layer, thus improving (as a “collector” and recombination center) the light emission intensity compared to a similar LET structure without QWs in the base. Gigahertz operation of the QW LET with simultaneously amplified electrical output and an optical output with signal modulation is demonstrated.
TL;DR: Surprisingly, large enhancement effects are achievable in both waveguides and nanocavities, and enhanced emission in the waveguide is shown to scale proportionally (inversely) with the photon group index (velocity).
Abstract: A theoretical formalism is presented to investigate enhanced radiative decay of excited dipoles in photonic crystal waveguides and nanocavities with a view to achieving efficient single-photon emission from embedded quantum dots. Surprisingly, large enhancement effects are achievable in both waveguides and nanocavities, and enhanced emission in the waveguide is shown to scale proportionally (inversely) with the photon group index (velocity). Further, a way to include radiative coupling of the quantum dot is shown, and the importance of its inclusion is subsequently demonstrated.
TL;DR: In this article, a silicon nanostructured pn junction diode using current injection at room temperature was observed to exhibit stimulated emission at bandgap energy of 1.1 eV, where the spatial confinement of carriers through such localization structures contributes to the enhancement of the stimulated emission.
Abstract: Stimulated emission at bandgap energy of 1.1 eV was observed in a silicon nanostructured pn junction diode using current injection at room temperature. Nonuniform diffusion using spin-on boron dopant mixed with silicon dioxide nanoparticles was used to fabricate the device. The spatial confinement of carriers through such localization structures contributes to the enhancement of the stimulated emission. The experimental results show a drastic increase in the optical power and multiple spectral peaks at wavelengths longer than the main peak of spontaneous emission through various phonon-assisted radiative recombination processes. When the injection current significantly exceeds a threshold, a single peak dominates, exhibiting stimulated emission.
TL;DR: In this paper, a lasing threshold was observed on the 0-1 emission band near 425 nm at excitation fluences as low as 0.5 μJ/cm2 (6×1016 cm−3 equivalent density), near the onset of density-dependent recombination processes.
Abstract: We report on the observation of amplified spontaneous emission and random lasing in self-organized crystalline para-sexiphenyl nanofibers. Using subpicosecond excitation, a lasing threshold is observed on the 0–1 emission band near 425 nm at excitation fluences as low as 0.5 μJ/cm2 (6×1016 cm−3 equivalent density), near the onset of density-dependent recombination processes. The dependence of the nonlinear emission spectrum on both the pump intensity and position of the excitation area are attributed to the interplay between random lasing and amplified spontaneous emission occurring along the nanofibers.
TL;DR: In this paper, the authors showed that the thermal excitation of holes from the quantum wells into the waveguide where they recombine, but not Auger recombination, limits the continuous-wave room-temperature output power of In(Al)GaAsSb/GaSb diode lasers.
Abstract: Measurements of gain, loss, threshold current, device efficiency and spontaneous emission of 2.5?2.82 ?m In(Al)GaAsSb/GaSb quantum-well diode lasers have been performed over a wide temperature range. The experimental results show that the thermal excitation of holes from the quantum wells into the waveguide where they recombine, but not Auger recombination, limits the continuous-wave room-temperature output power of these lasers, at least up to ? = 2.82 ?m. An approach to extend the wavelength of In(Al)GaAsSb/GaSb diode lasers beyond 3 ?m is discussed.
TL;DR: In this paper, a theoretical model for the linear optical gain properties of a quantum wire assembly and compare it to the well known case of quantum dot assembly was described and analyzed using bias dependent room temperature amplified spontaneous emission spectra.
Abstract: We describe a theoretical model for the linear optical gain properties of a quantum wire assembly and compare it to the well known case of a quantum dot assembly. We also present a technique to analyze the gain of an optical amplifier using bias dependent room temperature amplified spontaneous emission spectra. Employing this procedure in conjunction with the theoretical gain model, we demonstrate that InAs/InP quantum dash structures have quantum-wire-like characteristics. The procedure was used to extract the net gain coefficient, the differential gain, and the relative current component contributing to radiative recombination.
TL;DR: In this article, simultaneous amplified spontaneous emission from two different multiexcitonic transitions −1Se −1S3∕2 and 1Pe −1P3 ∕2− of colloidal CdSe nanocrystals (NCs) stabilized in high volume fraction in titania matrices was reported.
Abstract: We report simultaneous amplified spontaneous emission from two different multiexcitonic transitions −1Se–1S3∕2 and 1Pe–1P3∕2− of colloidal CdSe nanocrystals (NCs) stabilized in high volume fraction in titania matrices. Two-state lasing from both multiexcitonic transitions is achieved in a surface-emitting distributed feedback CdSe NC laser. Variable stripe length measurements show that the gain from the 1Pe–1P3∕2 transition is approximately twice that of the −1Se–1S3∕2 transition for 4.2nm radius CdSe∕ZnS core-shell NCs.
TL;DR: The results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated are presented.
Abstract: We present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also denote the dominant contribution of excitons to the luminescence signal, and the lack of thermodynamical equilibrium at low densities.
TL;DR: In this article, a thermal emission spectrum with a temperature of kT~7 keV modified by some absorption, which would be expected from an internally shocked hot bubble in a starburst region, can describe the spectrum.
Abstract: Prominent Fe K line emission is detected at around 6.7 keV in the XMM-Newton spectrum of the ultraluminous infrared galaxy Arp220. The continuum emission in the 2.5-10 keV band is flat and a few other spectral features are suggested. The large EW of the Fe K line poses a problem with interpreting the hard X-ray emission as integrated X-ray binary emission. A thermal emission spectrum with a temperature of kT~7 keV modified by some absorption, which would be expected from an internally shocked hot bubble in a starburst region, can describe the spectrum. An ensemble of radio supernovae in a dense environment, as suggested from VLBI imaging, could be another possibility, if frequent occurence of such powerful supernovae is sustained. However, the apparent lack of X-ray binary emission does not match the high supernova rate required by both interpretations. Highly photoionized, low-density gas illuminated by a hidden Compton-thick AGN is a possible alternative, which can be tested by presence/absence of radiative recombination continua in better quality data expected from a forthcoming observation.