Quantum Statistical Imaging of Particles without Restriction of the Diffraction Limit

A quantum measurement method based on the quantum nature of antibunching photon emission has been developed to detect single particles without the restriction of the diffraction limit. By simultaneously counting the single-photon and two-photon signals with fluorescence microscopy, the images of nearby nitrogen-vacancy centers in diamond at a distance of 8.5±2.4??nm have been successfully reconstructed. Also their axes information was optically obtained. This quantum statistical imaging technique, with a simple experimental setup, can also be easily generalized in the measuring and distinguishing of other physical properties with any overlapping, which shows high potential in future image and study of coupled quantum systems for quantum information techniques.

Phys.Rev.Lett.110,153901 (2013)

Theory of free space coupling to high-Q whispering gallery modes

A theoretical study of free space coupling to high-Q whispering gallery modes both in circular and deformed microcavities are presented. In the case of a circular cavity, both analytical solutions and asymptotic formulas are derived. The coupling efficiencies at different coupling regimes for cylinder incoming wave are discussed, and the maximum efficiency is estimated for the practical Gaussian beam excitation. In the case of a deformed cavity, the coupling efficiency can be higher if the excitation beam can match the intrinsic emission well and the radiation loss can be tuned by adjusting the degree of deformation. Employing an abstract model of slightly deformed cavity, we found that the asymmetric and peak like line shapes instead of the Lorentz-shape dip are universal in transmission spectra due to multi-mode interference, and the coupling efficiency can not be estimated from the absolute depth of the dip. Our results provide guidelines for free space coupling in experiments, suggesting that the high-Q ARCs can be efficiently excited through free space which will stimulate further experiments and applications of WGMs based on free space coupling.

Opt.Exp,Vol.21,Issue.8,9982-9995(2013)

Vector magnetic field sensing by a single nitrogen vacancy center in diamond

In this letter, we proposed and experimentally demonstrated a method to detect the vector magnetic field with a single nitrogen vacancy (NV) center in diamond. The magnetic field in parallel with the axis of the NV center can be obtained by detecting the electron Zeeman shift, while the Larmor precession of an ancillary nuclear spin close to the NV center can be used to measure the field perpendicular to the axis. Experimentally, both the Zeeman shift and Larmor precession can be measured through the fluorescence from the NV center. By applying additional calibrated magnetic fields, complete information on the vector magnetic field can be achieved with such a method. This vector magnetic-field detection method is insensitive to temperature fluctuation and it can be applied to nanoscale magnetic measurements.

EPL, 101,67003(2013)

Movable Fiber-Integrated Hybrid Plasmonic Waveguide on Metal Film

A waveguide structure consisting of a tapered nanofiber on a metal film is proposed and analyzed to support highly localized hybrid plasmonic modes. The hybrid plasmonic mode can be efficiently excited through the in-line tapered fiber based on adiabatic conversion and collected by the same fiber, which is very convenient in the experiment. Due to the ultrasmall mode area of plasmonic mode, the local electromagnetic field is greatly enhanced in this movable waveguide, which is potential for enhanced coherence light emitter interactions, such as waveguide quantum electrodynamics, single emitter spectrum and nonlinear optics.

Photon.Tech.Lett.24 434-436(2012)

Temperature dependent energy level shift of nitrogen-vacancy centers in diamond

Magnetic resonance and fluorescence spectra were measured for nitrogen-vacancy (NV) color centers ensemble in high purity diamond sample, with temperature ranging from 5.6 to 295 K. Both microwave and optical transition energies showed similar nonlinear temperature dependent characters, mainly originating from the thermal expansion of diamond. The present result demonstrated the necessary of taking temperature fluctuation into consideration for high temperature, as the frequency shift will reduce the fidelity of resonance controlling. For temperature below 100 K, these two energy transitions showed a tendency to be constant, which indicated higher stability and performance in applications with NV centers.

Appl.Phys.Lett.99,161903(2011)

Broadband Integrated Polarization Beam Splitter with Surface Plasmon

A broadband integrated waveguide polarization beam splitter consisting of a metal nanoribbon and two dielectric waveguides is proposed and numerically investigated. This surface plasmon based device provides a unique approach for polarization sensitive manipulation of light in an integrated circuit and will be essential for future classical and quantum information processes.

Opt. Lett. 36, 3630 (2011)

Negative Goos–Hanchen shift on a concave dielectric interface

We study the Goos–Hanchen shift (GHS) on a curved surface through numerical simulation by the boundary element method. A negative GHS is first discovered on a concave dielectric interface below the critical angle, accompanied by a large positive GHS on the convexity. The simulation shows that the GHS on a planar interface is the composition of the GHS from a concave and the corresponding convex interface. This work will enrich the study of the GHS for different curved surfaces, which will have potential applications in micro-optics and near-field optics.

Opt. Lett. 36, 624-626 (2011)

Plasmonic modes of silver nanowire on a silica substrate

Plasmon mode in a silver nanowire is theoretically studied when the nanowire is placed on or near a silica substrate. It is found that the substrate has much influence on the plasmon mode. For the nanowire on the substrate, the plasmon (hybrid) mode possesses not only a long propagation length but also an ultrasmall mode area. From the experimental point of view, this cavity-free structure holds a great potential to study a strong coherent interaction between the plasmon mode and single quantum system (for example, quantum dots) embedded in the substrate.

Appl. Phys. Lett. 97, 183102 (2010) ( APL's monthly top 20 most-downloaded articles )

Anti-bunching and luminescence blinking suppression from plasmon-interacted single CdSe/ZnS quantum dot

CdSe/ZnS colloidal quantum dots generally exist as blinking phenomena during the luminescence process that remarkably influences its applications. In this work, we used the surface plasmonic effect to effectively modulate single quantum dots. Obvious contrasts have been observed by comparing single quantum dots on silica and gold films. The surface plasmon is shown to obviously suppress the blinking of single quantum dots. With further demonstrated second- order correlation measurements, an anti-bunching effect was observed. The anti-bunching dip gives the smallest value of g(2)(0) = 0.15, and the lifetime of the exciton has been reduced. This method presents the application’s potential towards tunable high-emitting-speed single photon sources at room temperature

Opt. Express 18, 6340-6346 (2010)?

Photoluminescence from site-selected coupling between quantum dots and microtoroid cavities

By using CdSe/ZnS quantum dots (QDs), we study the effect of cavity quantum electrodynamics on the coupling of the microtoroid cavity. When with whispering gallery (WG) modes, the microtoroid cavity demonstrates high quality factor and small mode volume at visible wavelengths. Accordingly, fiber tapers allow QDs to adhere into the cavity and further permit the control of site-selected coupling. From the luminescence spectra, QDs are modulated effectively by cavity modes. Variable modulations are observed by changing QD coupling conditions. Therefore, based on experimental and theoretical research, strong and tunable Purcell enhancement can be realized by this system.

Chinese Optics Letter, 8, 709 (2010)

Mechanism of unidirectional emission of ultrahigh Q Whispering Gallery mode in microcavities

The mechanism of unidirectional emission of high Q Whispering Gallery mode in deformed circular micro- cavities is studied and firstly presented in this paper. In phase space, light in the chaotic sea leaks out the cavity through the refraction regions, whose positions are controlled by stable islands. Moreover, the positions of fixed points according to the critical line in unstable manifolds mainly determines the light leak out from which refraction region and the direction of the emission. By controlling the cavity shape, we can tune the leaky regions, as well as the positions of fixed points, to achieve unidirectional emission high Q cavities with narrow angular divergence both in high and low refractive index materials. specially for high index material, almost all Gibbous-shaped cavitiess have unidirectional emission.

arXiv:0908.3531

Modified transmission spectrum induced by two-mode interference in a single silica microsphere

We theoretically and experimentally study the resonant transmission spectrum of light in a fibre taper coupled with a single silica microsphere cavity system, where two whispering-gallery modes (WGMs) are simultaneously excited. By changing the taper position (correspondingly, tuning the resonant frequencies of the two WGMs and modulating their coupling conditions with the fibre taper), a sharp electromagnetically-induced- transparency-like window can be observed in the transmission spectrum. This line shape origins from the taper-mediated interference between two co-existing WGMs in a single microsphere. This measurement result agrees well with the theoretical analysis.

J. Phys. B: At. Mol. Opt. Phys. 42 215401 (2009)?Selected as?J. Phys. B's 2009 Highlights link

Ringing phenomenon in silica microsphere

Whispering gallery modes in silica microspheres are excited by a tunable continuous-wave laser through the fiber taper. Ringing phenomenon can be observed with high frequency sweeping speed. The thermal nonlinearity in the microsphere can enhance this phenomenon. Our measurement results agree very well with the theoretical predictions by the dynamic equation.

Chinese Optical Letters, 7, 299-301 (2009).

Inherently directional lasing from a thermal induced deformation high-Q microcavity

We experimentally report an asymmetrical spherical microcavity with thermal-induced deformation, in which five-bounce whispering-gallery modes possess not only ultrahigh quality factors (Q) but also remarkably directional escape emission from the microsphere boundary. With efficient free-space excitation and collection, a low-threshold microlaser is demonstrated and exhibits a highly directional emission. Our measurement agrees well with the theoretical predictions by corrected Fresnel law.

Opt. Lett. 34, 509-511 (2009)