Excitation of atoms in an optical lattice driven by polychromatic amplitude modulation

We investigate the mutiphoton process between different Bloch states in an amplitude modulated optical lattice. In the experiment, we perform the modulation with more than one frequency components, which includes a high degree of freedom and provides a flexible way to coherently control quantum states. Based on the study of single frequency modulation, we investigate the collaborative effect of different frequency components in two aspects. Through double frequency modulations, the spectrums of excitation rates for different lattice depths are measured. Moreover, interference between two separated excitation paths is shown, emphasizing the influence of modulation phases when two modulation frequencies are commensurate. Finally, we demonstrate the application of the double frequency modulation to design a large-momentum-transfer beam splitter. The beam splitter is easy in practice and would not introduce phase shift between two arms.Comment: 11pages, 7 figure

Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion

The superradiant Rayleigh scattering using a pump laser incident along the short axis of a Bose-Einstein condensate with a density distortion is studied, where the distortion is formed by shocking the condensate utilizing the residual magnetic force after the switching-off of the trapping potential. We find that very small variation of the atomic density distribution would induce remarkable asymmetrically populated scattering modes by the matter-wave superradiance with long time pulse. The optical field in the diluter region of the atomic cloud is more greatly amplified, which is not an ordinary mode amplification with the previous cognition. Our numerical simulations with the density envelop distortion are consistent with the experimental results. This supplies a useful method to reflect the geometric symmetries of the atomic density profile by the superradiance scattering.Comment: 7pages,4 figures, Optical Express 21,(2013)1437

Long-time nonlinear dynamical evolution for P-band ultracold atoms in an optical lattice

We report the long-time nonlinear dynamical evolution of ultracold atomic gases in the P-band of an optical lattice. A Bose-Einstein condensate (BEC) is fast and efficiently loaded into the Pband at zero quasi-momentum with a non-adiabatic shortcut method. For the first one and half milliseconds, these momentum states undergo oscillations due to coherent superposition of different bands, which are followed by oscillations up to 60ms of a much longer period. Our analysis shows the dephasing from the nonlinear interaction is very conducive to the long-period oscillations induced by the variable force due to the harmonic confinement.Comment: 8 pages, 7 figure

Research data supporting "High carrier mobility along the [111] orientation in Cu2O photoelectrodes"

Included in the dataset are detailed information into the crystallography, morphology, electronic properties, (photo)electrochemical and carrier dynamics of both single-crystal Cu2O thin films and polycrystalline Cu2O with favored crystal orientations. Multiple intruments, including Empyrean X-ray Diffractometer, Zeiss Merlin Scanning Electron Microscope, Tecnai Osiris Transmission Electron Micrisocope, Newport LCS-100 Solar Simulator, Biologic SP-200, GC9790plus Gas Chromatograph, Keithley 2450 SourceMeter, Shimadzu UV-3600 Plus Double-beam Spectrophotometer, were applied to collect the data. Abstract of associated publication: Solar fuels offer a promising approach to provide sustainable fuels by harnessing sunlight. Following a decade of advancement, Cu2O photocathodes are capable of delivering a performance comparable to that of photoelectrodes with established photovoltaic materials. However, considerable bulk charge carrier recombination that is poorly understood still limits further advances in performance. Here we demonstrate performance of Cu2O photocathodes beyond the state-of-the-art by exploiting a new conceptual understanding of carrier recombination and transport in single-crystal Cu2O thin films. Using ambient liquid-phase epitaxy, we present a new method to grow single-crystal Cu2O samples with three crystal orientations. Broadband femtosecond transient reflection spectroscopy measurements were used to quantify anisotropic optoelectronic properties, through which the carrier mobility along the [111] orientation was found to be an order of magnitude higher than those along other orientations. Driven by these findings, we developed a polycrystalline Cu2O photocathode with an extraordinarily pure (111) orientation and (111) terminating facets using a simple and low-cost method, which delivers 7 mA cm−2 current density (more than 70% improvement compared to that of state-of-the-art electrodeposited devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G illumination, and stable operation over at least 120 h.European Research Council (HYPERION, grant 756962) Engineering and Physical Sciences Research Council (grant H2CAT, EP/V012932/1) Swiss National Science Foundation (P2ELP2_195109) Engineering and Physical Sciences Research Council (EP/ T001038/1) UK Research and Innovation (EP/X022986/1) St John’s College Cambridge (Title A) European Research Council (MatEnSAP, 682833) UK Research and Innovation (EP/X030563/1) National Natural Science Foundation of China (52072187, 22122903) National Key Research and Development Program of China (019YFE0123400) Royal Society and Tata Group (UF150033