Fano-like Resonance due to Interference with Distant Transitions.

Narrow optical resonances of atoms or molecules have immense significance in various precision measurements, such as testing fundamental physics and the generation of primary frequency standards. In these studies, accurate transition centers derived from fitting the measured spectra are demanded, which critically rely on the knowledge of spectral line profiles. Here, we propose a new mechanism of Fano-like resonance induced by distant discrete levels and experimentally verify it with Doppler-free spectroscopy of vibration-rotational transitions of CO_{2}. The observed spectrum has an asymmetric profile and its amplitude increases quadratically with the probe laser power. Our results facilitate a broad range of topics based on narrow transitions.

Angiotensin II type 1 receptor gene A1166C polymorphism and breast cancer susceptibility.

Numerous studies have evaluated the association between the angiotensin II type-1 receptor (AGTR1) gene A1166C polymorphism and breast cancer risk. However, the specific association is controversial. The aim of the present study was to derive a more precise estimation of the relationship. A comprehensive research was conducted of the PubMed and the Google Scholar databases through February 2015. Data were assessed using STATA version 12.0. Pooled odds ratios with 95%CIs were derived from the fixed-effect or random-effect models. A total of 911 patients with breast cancer and 1284 controls from 5 case-control studies were included in this meta-analysis. The meta-analysis results showed no significant association between the AGTR1 gene A1166C polymorphism and breast cancer risk. Similarly, in the subgroup analysis regarding ethnicity, no associations were observed. Heterogeneity and publication bias were not observed in this meta-analysis. The A1166C polymorphism in the AGTR1 gene may not be a risk factor for breast cancer. Further, large, and well-designed studies are needed to confirm this conclusion.

Towards Scalable Entangled Photon Sources with Self-Assembled InAs/GaAs Quantum Dots.

The biexciton cascade process in self-assembled quantum dots (QDs) provides an ideal system for realizing deterministic entangled photon-pair sources, which are essential to quantum information science. The entangled photon pairs have recently been generated in experiments after eliminating the fine-structure splitting (FSS) of excitons using a number of different methods. Thus far, however, QD-based sources of entangled photons have not been scalable because the wavelengths of QDs differ from dot to dot. Here, we propose a wavelength-tunable entangled photon emitter mounted on a three-dimensional stressor, in which the FSS and exciton energy can be tuned independently, thereby enabling photon entanglement between dissimilar QDs. We confirm these results via atomistic pseudopotential calculations. This provides a first step towards future realization of scalable entangled photon generators for quantum information applications.

Locality and universality of quantum memory effects.

The modeling and analysis of the dynamics of complex systems often requires to employ non-Markovian stochastic processes. While there is a clear and well-established mathematical definition for non-Markovianity in the case of classical systems, the extension to the quantum regime recently caused a vivid debate, leading to many different proposals for the characterization and quantification of memory effects in the dynamics of open quantum systems. Here, we derive a mathematical representation for the non-Markovianity measure based on the exchange of information between the open system and its environment, which reveals the locality and universality of non-Markovianity in the quantum state space and substantially simplifies its numerical and experimental determination. We further illustrate the application of this representation by means of an all-optical experiment which allows the measurement of the degree of memory effects in a photonic quantum process with high accuracy.

Linear up-conversion of orbital angular momentum.

We experimentally demonstrated that infrared light imprinted with orbital angular momentum (OAM) was linearly converted into visible light using four-wave mixing (FWM) via a ladder-type configuration in 85Rb atoms. Simultaneously, we theoretically simulated this linear conversion process, and the theoretical analysis was in reasonable agreement with the experimental results. A large single-photon detuning process was used to reduce the absorption of the atoms to the up-converted light and to avoid pattern formation in the FWM process. The multi-mode image linear conversion process is important for applications including image communications, astrophysics, and quantum information.

Molecular-spin dynamics study of electromagnons in multiferroic RMn2O5.

We investigate the electromagnon in magnetoferroelectrics RMn(2)O(5) using combined molecular-spin dynamics simulations. We confirm that the origin of the electromagnon modes observed in the optical spectra is due to the exchange-striction interaction between the magnons and the phonons, and the dielectric step at the magnetic phase transition is due to the appearance of the electromagnon in the low-temperature phase in these materials. The magnetic anisotropy breaks the rotational symmetry of the magnetic structures and, as a result, the electromagnon splits into three modes in RMn(2)O(5). We find that the electromagnon frequencies are very sensitive to the magnetic wavevector along the a direction q(x). Therefore, the electromagnon frequencies of TmMn(2)O(5) (q(x) ~ 0.467) are expected to be much higher than those of other materials of the family, such as R= Tb, Y, Ho, etc (q(x) ~ 0.48). We further calculate the electromagnons in the magnetic field, and find a new mode appearing in the magnetic field. Although the modes' frequencies change significantly under magnetic field, the total static dielectric constant contributed from the electromagnons does not change much in the magnetic field, suggesting that the colossal magnetodielectric effects in these materials may not be caused by the electromagnons.

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.

Electronic structure interpolation via atomic orbitals.

We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.

Negative Goos-Hänchen shift on a concave dielectric interface.

We study the Goos-Hänchen 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.

Systematically improvable optimized atomic basis sets for ab initio calculations.

We propose a unique scheme to construct fully optimized atomic basis sets for density-functional calculations. The shapes of the radial functions are optimized by minimizing the spillage of the wavefunctions between the atomic orbital calculations and the converged plane wave results for dimer systems. The quality of the bases can be systematically improved by increasing the size of the bases within the same framework. We show that the spillage can describe the convergency of the total energy very well and the cutoff radii of the atomic orbitals are extremely important for the quality of the atomic orbitals. The scheme is easy to implement and very flexible. We have performed extensive tests of this scheme for a wide variety of systems, including semiconductors, oxides, metals, clusters, etc. The results show that the obtained atomic bases are very satisfactory for both accuracy and transferability.

Low-threshold microlaser in a high-Q asymmetrical 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.

Stimulated emission as a result of multiphoton interference.

By performing an experiment on stimulated emission by two photons in the parametric amplification process and comparing it to a three-photon interference scheme, we present evidence in support of the idea that the underlying physics of stimulated emission is simply the constructive interference due to photon indistinguishability. So the observed signal enhancement upon the input of photons can be interpreted as a result of multiphoton interference of the input photons and the otherwise spontaneously emitted photon from the amplifier.

Four-photon interference with asymmetric beam splitters.

Two experiments of four-photon interference are performed with two pairs of photons from parametric downconversion with the help of asymmetric beam splitters. The first experiment is a generalization of the Hong-Ou-Mandel interference effect to two pairs of photons while the second one utilizes this effect to demonstrate a four-photon de Broglie wavelength of lambda/4 by projection measurement.

Demonstration of temporal distinguishability in a four-photon state and a six-photon state.

An experiment is performed to demonstrate the temporal distinguishability of a four-photon state and a six-photon state, both from parametric down-conversion. The experiment is based on a multiphoton interference scheme in a recently discovered projection measurement of a maximally entangled N-photon state. By measuring the visibility of the interference dip, we can distinguish the various scenarios in the temporal distribution of the pairs and, thus, quantitatively determine the degree of temporal distinguishability of a multiphoton state.