Showing papers on "Quantum dot laser published in 2008"
TL;DR: It is shown that a single quantum dot coupled to a photonic crystal nanocavity can facilitate controlled phase and amplitude modulation between two modes of light at the single-photon level.
Abstract: Optical nonlinearities enable photon-photon interaction and lie at the heart of several proposals for quantum information processing, quantum nondemolition measurements of photons, and optical signal processing. To date, the largest nonlinearities have been realized with single atoms and atomic ensembles. We show that a single quantum dot coupled to a photonic crystal nanocavity can facilitate controlled phase and amplitude modulation between two modes of light at the single-photon level. At larger control powers, we observed phase shifts up to π/4 and amplitude modulation up to 50%. This was accomplished by varying the photon number in the control beam at a wavelength that was the same as that of the signal, or at a wavelength that was detuned by several quantum dot linewidths from the signal. Our results present a step toward quantum logic devices and quantum nondemolition measurements on a chip.
426 citations
TL;DR: High fidelity initialization of a single hole spin confined to a self-assembled quantum dot by optical pumping is demonstrated, demonstrating a negligible hole spin hyperfine interaction and suggesting a route to the realization of solid-state quantum networks that can intra-convert the spin state with the polarization of a photon.
Abstract: A quantum dot that can be optically initialized to contain a well-defined and very stable hole spin has been designed, with a relaxation time long enough to allow potential applications in solid-state quantum networks.
354 citations
TL;DR: Using far-field optical lithography, a single quantum dot is positioned within a pillar microcavity with a 50 nm accuracy with a milestone for quantum computing.
Abstract: Using far-field optical lithography, a single quantum dot is positioned within a pillar microcavity with a 50 nm accuracy. The lithography is performed in situ at 10 K while measuring the quantum dot emission. Deterministic spectral and spatial matching of the cavity-dot system is achieved in a single step process and evidenced by the observation of strong Purcell effect. Deterministic coupling of two quantum dots to the same optical mode is achieved, a milestone for quantum computing.
320 citations
TL;DR: Quasi-three-level solid state solid-state lasers using trivalent rare earth ions are efficient sources in the near and mid-infrared spectral regions as mentioned in this paper, and their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes.
Abstract: Quasi-three-level solid-state lasers using trivalent rare earth ions are efficient sources in the near- and mid-infrared spectral regions. Their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes. This work will give an overview of quasi-three-level solid-state lasers emitting in the wavelength range 1–5 μm. Recent research and advances in spectroscopic and laser results will be presented. In comparison to four-level lasers such as e.g. Nd3+ lasers at 1.06 μm, quasi-three-level lasers show a much stronger influence of temperature on laser performance, mainly due to the thermally induced changes in the spectroscopic properties of the laser medium. Nevertheless, highly efficient lasers can be realized by direct diode pumping with high spatial and spectral brightness laser diodes. The population dynamics in the manifolds also play an important role and ion concentrations are used to minimize or maximize energy-transfer effects. These general topics will be addressed in Sect. 1, in which basic aspects of quasi-three-level lasers and their description are discussed. Section 2 deals with the general energy-level structure of trivalent rare earths in hosts, from which the most interesting ions and their transitions can be derived. These ions, Nd3+, Yb3+, Er3+, Tm3+ and Ho3+, are investigated in detail in Sect. 3 in order of their emission wavelengths, focusing on their spectral properties and laser results in different laser architectures and host media. In Sect. 4 the work is finally summarized.
276 citations
TL;DR: The quantum magnetic phase transition between two different Kondo regimes is achieved by tuning gate voltages and is fundamentally different from previously observed Kondo transitions in semiconductor and nanotube quantum dots.
Abstract: Quantum criticality is the intriguing possibility offered by the laws of quantum mechanics when the wave function of a many-particle physical system is forced to evolve continuously between two distinct, competing ground states. This phenomenon, often related to a zero-temperature magnetic phase transition, is believed to govern many of the fascinating properties of strongly correlated systems such as heavy-fermion compounds or high-temperature superconductors. In contrast to bulk materials with very complex electronic structures, artificial nanoscale devices could offer a new and simpler means of understanding quantum phase transitions. Here we demonstrate this possibility in a single-molecule quantum dot, where a gate voltage induces a crossing of two different types of electron spin state (singlet and triplet) at zero magnetic field. The quantum dot is operated in the Kondo regime, where the electron spin on the quantum dot is partially screened by metallic electrodes. This strong electronic coupling between the quantum dot and the metallic contacts provides the strong electron correlations necessary to observe quantum critical behaviour. The quantum magnetic phase transition between two different Kondo regimes is achieved by tuning gate voltages and is fundamentally different from previously observed Kondo transitions in semiconductor and nanotube quantum dots. Our work may offer new directions in terms of control and tunability for molecular spintronics.
233 citations
TL;DR: In this article, a terahertz quantum cascade laser source based on intracavity tera-hertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade with the active region engineered to possess giant second-order nonlinear susceptibility is presented.
Abstract: We report on our progress in the development of a terahertz quantum cascade laser source based on intracavity terahertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade laser with the active region engineered to possess giant second-order nonlinear susceptibility. In this letter, we demonstrate devices that operate in mid-infrared at λ1=8.9μm and λ2=10.5μm and produce terahertz output at λ≈60μm via difference-frequency generation with 7μW output power at 80K, 1μW output at 250K, and still approximately 300nW output at 300K.
223 citations
TL;DR: The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.
Abstract: We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.
215 citations
TL;DR: In this article, the authors reported the observation of thermal rectification in a semiconductor quantum dot, as inferred from the asymmetric line shape of the thermopower oscillations.
Abstract: We report the observation of thermal rectification in a semiconductor quantum dot, as inferred from the asymmetric line shape of the thermopower oscillations. The asymmetry is observed at high in-plane magnetic fields and caused by the presence of a high orbital momentum state in the dot.
199 citations
TL;DR: In this paper, a strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition and a maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm.
Abstract: A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.
195 citations
TL;DR: In this article, the authors quantitatively account for the observed 37% external quantum efficiency, showing that it results from the large depletion width and long carrier lifetime combined, and that the electron diffusion length of 0.1μm is comparable to neutral region width.
Abstract: PbS colloidal quantum dot photovoltaic devices in a Schottky architecture have demonstrated an infrared power conversion efficiency of 4.2%. Here, we elucidate the internal mechanisms leading to this efficiency. At relevant intensities, the drift length is 10μm for holes and 1μm for electrons. Transport within the 150nm wide depletion region is therefore highly efficient. The electron diffusion length of 0.1μm is comparable to neutral region width. We quantitatively account for the observed 37% external quantum efficiency, showing that it results from the large depletion width and long carrier lifetime combined.
192 citations
TL;DR: In this paper, the effect of various microscopic scattering processes on the gain profile as a function of temperature is discussed, and it is argued that increased broadening, primarily due to increased impurity scattering, and not diminishing population inversion, is the main reason for the reduction of peak gain.
Abstract: We study the rapid decrease of peak gain in resonant-phonon terahertz quantum cascade lasers with increasing temperature. The effect of various microscopic scattering processes on the gain profile as a function of temperature is discussed. We argue that increased broadening, primarily due to increased impurity scattering, and not diminishing population inversion, is the main reason for the reduction of peak gain.
TL;DR: By using strong optical injection locking, resonance frequency enhancement in excess of 100 GHz in semiconductor lasers is reported, showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for Resonance frequency enhancement.
Abstract: By using strong optical injection locking, we report resonance frequency enhancement in excess of 100 GHz in semiconductor lasers. We demonstrate this enhancement in both distributed feedback (DFB) lasers and vertical-cavity surface-emitting lasers (VCSELs), showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for resonance frequency enhancement. We have also identified the key factors that cause low-frequency roll-off in injection-locked lasers. By increasing the slave laser's DC current bias, we have achieved a record intrinsic 3-dB bandwidth of 80 GHz in VCSELs.
TL;DR: This work proposes a model where transport occurs through quantum dots that are nucleated by background disorder potential in the presence of a confinement gap, and indicates that dot size may scale with constriction width.
Abstract: Graphene nanoribbons display an imperfectly understood transport gap. We measure transport through nanoribbon devices of several lengths. In nanoribbons of length greater than or equal to 250 nm we observe transport through multiple quantum dots in series, while shorter constrictions of length less than or equal to 60 nm display behavior characteristic of single and double quantum dots. Dot size scales with constriction width. We propose a model where transport occurs through quantum dots that are nucleated by background disorder potentials in the presence of a confinement gap.
01 Jan 2008
TL;DR: InAs/GaAs Quantum Dots with multimodal Size Distribution as mentioned in this paper, InAs quantum Dots are grown by MOCVD for opto-electronic device applications.
Abstract: InAs/GaAs Quantum Dots with multimodal Size Distribution. -Capacitance Voltage Spectroscopy of InAs Quantum Dots. -Dynamics of carrier transfer into In(Ga)As self-assembled quantum dots. -Spin phenomena in self-assembled quantum dots. -Studies of Semiconductor Quantum Dots for Quantum Information Processing. -In(Ga)As/GaAs quantum dots grown by MOCVD for opto-electronic device applications. -Excitons and spins in quantum dots coupled to a continuum of states. -Quantum Coupling in Quantum Dot Molecules. -Stress relaxation phenomena in buried quantum dots. -Carrier transfer in the arrays of coupled quantum dots. -Detailed analysis of the shape-dependent deformation field in 3D Ge islands on Si(001. -Growth and Characterization of III-Nitride Quantum Dots and their Application to Emitters. -Metal-Mask MBE technique for selective-area-growth of InAs quantum dots towards optical integrated circuit applications.
TL;DR: In this paper, the authors analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linwidth) in monolithic passively mode-locked semiconductor lasers.
Abstract: We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Haus's model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.
04 May 2008
TL;DR: In this article, a passively modelocked VECSEL with both gain and saturable absorber integrated into a single semiconductor structure is proposed, referred to as the modelocked integrated external-cavity surface emitting laser (MIXSEL).
Abstract: We discuss a passively modelocked VECSEL with both gain and saturable absorber integrated into a single semiconductor structure. We refer to this new kind of laser as the modelocked integrated external-cavity surface emitting laser (MIXSEL).
TL;DR: In this paper, the authors report on electrically pumped high-Q quantum dot-micropillar cavities with quality factors of up to 16.000 and a special current injection scheme using a ring-shaped upper contact is presented which ensures an efficient light out-coupling through the uncapped upper surface of the micropillars.
Abstract: We report on electrically pumped high-Q quantum dot-micropillar cavities with quality factors of up to 16.000. A special current injection scheme using a ring-shaped upper contact is presented which ensures an efficient light out-coupling through the uncapped upper surface of the micropillar. The devices feature excellent single-quantum dot cavity quantum electrodynamic effects with a Purcell enhancement of about 10 for a micropillar with a diameter of 2.5μm.
TL;DR: In this paper, the authors demonstrate quantum cascade laser at an emitting wavelength of 4.6μm, which are capable of room temperature, high power continuous wave (cw) operation.
Abstract: We demonstrate quantum cascade lasers at an emitting wavelength of 4.6μm, which are capable of room temperature, high power continuous wave (cw) operation. Buried ridge geometry with a width of 9.8μm was utilized. A device with a 3mm cavity length that was epilayer-down bonded on a diamond submount exhibited a maximum output power of 1.3W at room temperature in cw operation. The maximum output power at 80K was measured to be 4W, with a wall plug efficiency of 27%.
TL;DR: It is shown that strong coupling (SC) of light and matter as it is realized with quantum dots in microcavities differs substantially from the paradigm of atoms in optical cavities.
Abstract: We show that strong coupling (SC) of light and matter as it is realized with quantum dots in microcavities differs substantially from the paradigm of atoms in optical cavities. The type of pumping used in semiconductors yields new criteria to achieve SC, with situations where the pump hinders, or on the contrary, favors it. We analyze one of the seminal experimental observation of SC of a quantum dot in a pillar microcavity [Reithmaier, Nature (London) 432, 197 (2004)10.1038/nature02969] as an illustration of our main statements.
TL;DR: In this paper, the radiative and nonradiative decay rates of InAs quantum dots are measured by controlling the local density of optical states near an interface, and from time-resolved measurements, they extract the oscillator strength and the quantum efficiency and their dependence on emission energy.
Abstract: The radiative and nonradiative decay rates of InAs quantum dots are measured by controlling the local density of optical states near an interface. From time-resolved measurements, we extract the oscillator strength and the quantum efficiency and their dependence on emission energy. From our results and a theoretical model, we determine the striking dependence of the overlap of the electron and hole wavefunctions on the quantum dot size. We conclude that the optical quality is best for large quantum dots, which is important in order to optimally tailor quantum dot emitters for, e.g., quantum electrodynamics experiments
04 May 2008
TL;DR: In this article, the authors report room-temperature, low threshold, multi-and single mode lasing in levitated microdrops doped with low concentrations of CdSe/ZnS core/shell quantum dots.
Abstract: We report room-temperature, low threshold, multi- and single mode lasing in levitated microdrops doped with low concentrations of CdSe/ZnS core/shell quantum dots.
TL;DR: For the first time, femtosecond pulses from a passive single-section InAs/InP quantum-dot (QD) mode-locked laser (MLL) with the active length of 456 microm and ridge width of 2.5 microm are reported.
Abstract: For the first time, we report femtosecond pulses from a passive single-section InAs/InP quantum-dot (QD) mode-locked laser (MLL) with the active length of 456 microm and ridge width of 2.5 microm at the C-band wavelength range. Without any external pulse compression, the transform-limited Gaussian-pulses are generated at the 92 GHz repetition rate with the 312 fs pulse duration, which is the shortest pulse from any directly electric-pumping semiconductor MLLs to our best knowledge. The lasing threshold injection current and external differential quantum efficiency are 17.2 mA and 38%, respectively. We have also investigated the working principles of the proposed QD MLLs.
TL;DR: It is shown that individual colloidal CdSe-core quantum dots can be optically trapped and manipulated in three dimensions by an infrared continuous wave laser operated at low laser powers, an important advantage for single molecule experiments.
Abstract: We show that individual colloidal CdSe-core quantum dots can be optically trapped and manipulated in three dimensions by an infrared continuous wave laser operated at low laser powers. This makes possible utilizing quantum dots not only for visualization but also for manipulation, an important advantage for single molecule experiments. Moreover, we provide quantitative information about the magnitude of forces applicable to a single quantum dot and of the polarizability of an individual quantum dot.
TL;DR: In this article, a single weakly coupled quantum dot can control the transmission of photons through a photonic crystal cavity that is coupled to waveguides on the chip and demonstrated dipole induced transparency.
Abstract: We demonstrate dipole induced transparency in an integrated photonic crystal device. We show that a single weakly coupled quantum dot can control the transmission of photons through a photonic crystal cavity that is coupled to waveguides on the chip. Control over the quantum dot and cavity resonance via local temperature tuning, as well as efficient out-coupling with an integrated grating structure is demonstrated.
TL;DR: This work demonstrates conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot.
Abstract: Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits.
04 May 2008
TL;DR: In this paper, the realization and modelling of microdisk lasers displaying vertical emission is described, which are THz quantum cascade lasers with metallic gratings fabricated along the circumference of the circumference.
Abstract: We report the realization and modelling of microdisk lasers displaying vertical emission. The devices are THz quantum cascade lasers with metallic gratings fabricated along the circumference.
TL;DR: In this article, a charging energy of 4.3 meV was extracted from Coulomb diamond measurements on a graphene quantum dot with an integrated graphene charge detector, which consists of a graphene island (diameter of ∼200 nm) connected to source and drain contacts via two narrow graphene constrictions.
Abstract: We report measurements on a graphene quantum dot with an integrated graphene charge detector. The quantum dot device consists of a graphene island (diameter of ∼200 nm) connected to source and drain contacts via two narrow graphene constrictions. From Coulomb diamond measurements a charging energy of 4.3 meV is extracted. The charge detector is based on a 45 nm wide graphene nanoribbon placed approximately 60 nm from the island. We show that resonances in the nanoribbon can be used to detect individual charging events on the quantum dot. The charging induced potential change on the quantum dot causes a steplike change in the current in the charge detector. The relative change in the current ranges from 10% up to 60% for detecting individual charging events.
TL;DR: In this paper, the effect of a surface acoustic wave (SAW) on the emission of a single InAs quantum dot was investigated, where the SAW caused the energy of the transitions within the dot to oscillate at the frequency of the SAW, producing a characteristic broadening of the emission lines in their timeaveraged spectra.
Abstract: This letter presents an experimental investigation into the effect of a surface-acoustic-wave (SAW) on the emission of a single InAs quantum dot. The SAW causes the energy of the transitions within the dot to oscillate at the frequency of the SAW, producing a characteristic broadening of the emission lines in their time-averaged spectra. This periodic tuning of the transition energy is used as a method to regulate the output of a device containing a single quantum dot and we study the system as a high-frequency periodic source of single photons.