In this paper we investigate the coherence properties of a quantum dot under two-photon resonant excitation in combination with an additional photo-neutralization laser. The photo-neutralization increases the efficiency of the excitation process and thus, the brightness of the source, by a factor of approximately 1.5 for biexciton-exciton pairs. This enhancement does not degrade the relevant coherences in the system; neither the single photon coherence time, nor the coherence of the excitation process.

We show that resonance fluorescence, i.e. the resonant emission of a coherently driven two-level system, can be realized with a semiconductor quantum dot. The dot is embedded in a planar optical micro-cavity and excited in a wave-guide mode so as to discriminate its emission from residual laser scattering. The transition from the weak to the strong excitation regime is characterized by the emergence of oscillations in the first-order correlation function of the fluorescence, g(τ ), as measured by interferometry. The measurements correspond to a Mollow triplet with a Rabi splitting of up to 13.3 µeV. Second-order-correlation measurements further confirm non-classical light emission. [3,4,5,6,7], as well as photon anti-bunching [8], and were previously only observable in isolated atoms or ions. In addition, QDs can be readily integrated into optical micro-cavities making them attractive for a number of applications, particularly quantum information processing and high efficiency light sources. For example, QDs could be used to realize deterministic solid-state single photon sources [9,10,11] and qubit-photon interfaces [12]. Advances in high-Q cavities have shown that not only can the spontaneous emission rate be dramatically increased by the Purcell effect [13,14], but emission can be reversed in the strong coupling regime [15,16,17]. Despite these efforts, however, quantum dot-based cavity quantum electrodynamics (QED) lacks an ingredient essential to the success of atomic cavity QED, namely the ability to truly resonantly manipulate the two-level system [9,10,11]. Current approaches can at best populate the dot in one of its excited states, which subsequently relaxes in some way to the emitting ground state. This incoherent relaxation has been addressed theoretically [18,19], and experimentally [20] but direct resonant excitation and collection in the ground state has so far not been reported as it is very challenging to differentiate the resonance fluorescence from same-frequency laser scattering off defects, contaminants, etc. In quantum dots without cavities, coherent manipulation of ground-state excitons has nonetheless been achieved with a number of techniques including differential transmission [6], differential * Electronic address: shih@physics.utexas.edu reflectivity [21], four-wave mixing [22], photodiode spectroscopy [7], and Stark-shift modulation absorption spectroscopy [23]. However, none of these is able to collect and use the actual photon emission which limits their use in many potential applications of QDs. This report presents the first measurement of resonance fluorescence in a single self-assembled quantum dot. Described by Mollow in 1969 [24], the resonant emission of a two-state quantum system under strong coherent excitation is distinguished by an oscillatory first-order correlation function, g(τ ), that we observe with interferometry. We use a planar optical micro-cavity to guide the excitation laser between the cavity mirrors and simultaneously enhance the single photon emission in th...

Macrolides, which comprise a family of lactones with different ring sizes, belong to the polyketide class of natural products. Resorcinolic macrolides, an important subgroup, possess interesting structures and exhibit a wide variety of bioactivities, such as anti-tumor, anti-bacteria, and anti-malaria activities, etc. This review summarizes progress in isolation, bioactivity studies, biosynthesis, and representative chemical syntheses of this group of macrolides in recent decades, encompassing 63 naturally occurring macrolides published in 120 articles.

Spontaneous self-sustained chaotic current oscillations are observed experimentally in lightly-doped weakly-coupled GaAs/ Al 0.45 Ga 0.55 As superlattices at room temperature for the first time. The mole fraction of Aluminum in the barrier is chosen to be 0.45 to suppress the thermal carrier leakage through the X-band valley. The effective nonlinearity induced by the sequential well-to-well resonant tunneling can still be strong enough to induce spontaneous chaotic current oscillations even at room temperature. The frequency spectrum of the chaotic current oscillations is ranged from DC to 4 GHz, which can be used as ultra-wide-band noise sources with a bandwidth of several Giga Hertz. The study of semiconductor superlattices (SLs), one of the typical low dimensional structures, has formed a major branch of solid-state physics [1]. In 1970, Esaki and Tsu proposed the concept of superlattices that the bulky Brillouin zone can be folded by several tens of time through superlattice effects [2]. Electrons in the center of the shrunk Brillouin zone could be easily drifted into the boundary that negative differential conductance (NDC) could be resulted from, which was expected to used as microwave oscillation resources with a frequency much larger than that of Gunn diodes. However, there are almost no practical applications yet even though the periodic self-sustained current oscillations were be realized in SLs [3,4], since the oscillation frequency cannot achieved to be large as expected and the overall performance was not comparable with GaAs-or InP-based HEMT devices. Another kind of NDC effect was observed experimentally in weakly-coupled SLs induced by well-to-well sequential resonant tunneling [5]. A lightly-doped weak-coupled SL represent as an ideal one-dimensional nonlinear dynamical system with many degrees of freedom, and the effective nonlinearity is originated from NDC. Indeed, there were a diversify of spatio-temporal patterns observed in DC biased SLs, such as static high-field domains, self-sustained periodic current oscillations, quasi-periodic current oscillations and spontaneous chaotic current oscillations, etc. These spatio-temporal patterns can be observed only below liquid-nitrogen temperature range except that the periodic current oscillations with a frequency range of several GHz were realized at room temperature [6,7].The occurrence of chaos in a dynamical system relies on much more nonlinearity than that of periodicity. The increase of temperature would reduce the nonlinearity in weakly-coupled SLs. The nonlinearity in SLs is characterized by NDC resulted from the well-to-well sequential resonant tunneling. There are two mechanisms that are responsible for the degradation of the nonlinearity induced by the increasing temperature. As the temperature is increased, the resonant tunneling process would be disturbed by the en-