Shengwang Du

Oxygen‐Assisted Charge Transfer Between ZnO Quantum Dots and Graphene

Efficient charge transfer between ZnO quantum dots (QDs) and graphene is demonstrated by decorating ZnO QDs on top of graphene, with the assistance of oxygen molecules from the air. The electrical response of the device to UV light is greatly enhanced, and a photoconductive gain of up to 10(7) can be obtained.

Electro-optic Modulation of Single Photons

We use the Stokes photon of a biphoton pair to set the time origin for electro-optic modulation of the wave function of the anti-Stokes photon thereby allowing arbitrary phase and amplitude modulation. We demonstrate conditional single-photon wave functions composed of several pulses, or instead, having Gaussian or exponential shapes.

Discussion and Outlook

We discuss the potential applications of optical precursors. Precursor fields are generated from the linear dispersion effect, such that the precursor fields can be stacked to achieve extremely high transient pulse. Another application in pulse manipulation is stimulated by the precursor generated from phase step-modulation, which may be applied to differential phase shifted key scheme. Communication in dense material is another possible application of precursor. Constructed from far off-resonance spectral components regardless of specific medium, precursor finds further advantage in communication under water.

Coherent Optical Memory with High Storage Efficiency and Large Fractional Delay

A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation.

A Mitochondrion-Specific Photoactivatable Fluorescence Turn-On AIE-Based Bioprobe for Localization Super-Resolution Microscope

A novel mitochondrion-specific photo-activatable fluorescence turn-on bioprobe, named as o-TPE-ON+, is designed and readily prepared, operating through a new photoactivatable mechanism of photocyclodehydrogenation. This bioprobe exhibits unique photoactivation behavior in cells, and is applied to super-resolution imaging of mitochondrion and its dynamic investigation in both fixed and live cells under physiological conditions without any external additives.

Piezotronic Effects on the Optical Properties of ZnO Nanowires

We report the piezotronic effects on the photoluminescence (PL) properties of bent ZnO nanowires (NWs). We find that the piezoelectric field largely modifies the spatial distribution of the photoexcited carriers in a bent ZnO NW. This effect, together with strain-induced changes in the energy band structure due to the piezoresistive effects, results in a net redshift of free exciton PL emission from a bent ZnO NW. At the large-size limit, this net redshift depends only on the strain parameter, but it is size-dependent if the diameter of the NW is comparable to that of the depletion layer. The experimental data obtained using the near-field scanning optical microscopy technique at low temperatures support our theoretical model.

Narrowband biphoton generation near atomic resonance

Generating nonclassical light offers a benchmark tool for fundamental research and potential applications in quantum optics. Conventionally, it has become a standard technique to produce nonclassical light through the nonlinear optical processes occurring in nonlinear crystals. We describe this process using cold atomic-gas media to generate such nonclassical light, especially focusing on narrowband biphoton generation. Compared with the standard procedure the new biphoton source has such properties as long coherence time, long coherence length, high spectral brightness, and high conversion efficiency. Although there exist two methodologies describing the physical process, we concentrate on the theoretical aspect of the entangled two-photon state produced from the four-wave mixing in a multilevel atomic ensemble using perturbation theory. We show that both linear and nonlinear optical responses to the generated fields play an important role in determining the biphoton waveform and, consequently, on the two-photon temporal correlation. There are two characteristic regimes determined by whether the linear or nonlinear coherence time is dominant. In addition, our model provides a clear physical picture that brings insight into understanding biphoton optics with this new source. We apply our model to recent work on generating narrowband (and even subnatural linewidth) paired photons using the technique of electromagnetically induced transparency and slow-light effect in cold atoms and find good agreement with experimental results.

Electromagnetically induced Talbot effect

By modulating transmission function of a weak probe field via a strong control standing wave, an electromagnetically induced grating can be created in the probe channel. Such a nonmaterial grating may lead to self-imaging of ultracold atoms or molecules in the Fresnel near-field regime. This work may offer a nondestructive and lensless way to image ultracold atoms or molecules.

Optical storage with electromagnetically induced transparency in a dense cold atomic ensemble

We experimentally investigate optical storage with electromagnetically induced transparency in a dense cold (85)Rb atomic ensemble. By varying the optical depth (OD) from 0 to 140, we observe that the optimal storage efficiency has a saturation value of 50% as OD>50. Our result is consistent with that obtained from hot vapor cell experiments.

Optimal storage and retrieval of single-photon waveforms

We report an experimental demonstration of optimal storage and retrieval of heralded single-photon wave packets using electromagnetically induced transparency (EIT) in cold atoms at a high optical depth. We obtain an optimal storage efficiency of (49 ± 3)% for single-photon waveforms with a temporal likeness of 96%. Our result brings the EIT quantum light-matter interface closer to practical quantum information applications.