Generation of Narrow-Band Polarization-Entangled Photon Pairs for Atomic Quantum Memories

We report an experimental realization of a narrow-band polarization-entangled photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous parametric down-conversion. This linewidth is comparable to the typical linewidth of atomic ensemble based quantum memories. Single-mode output is realized by setting a reasonable cavity length difference between different polarizations, using of temperature controlled etalons and actively stabilizing the cavity. The entangled property is characterized with quantum state tomography, giving a fidelity of 94% between our state and a maximally entangled state. The coherence length is directly measured to be 32 m through two-photon interference.Comment: 4 pages, 4 figure

Miniaturization of Branch-Line Coupler Using Composite Right/Left-Handed Transmission Lines with Novel Meander-shaped-slots CSSRR

A novel compact-size branch-line coupler using composite right/left-handed transmission lines is proposed in this paper. In order to obtain miniaturization, composite right/left-handed transmission lines with novel complementary split single ring resonators which are realized by loading a pair of meander-shaped-slots in the split of the ring are designed. This novel coupler occupies only 22.8% of the area of the conventional approach at 0.7 GHz. The proposed coupler can be implemented by using the standard printed-circuit-board etching processes without any implementation of lumped elements and via-holes, making it very useful for wireless communication systems. The agreement between measured and stimulated results validates the feasible configuration of the proposed coupler

Two-dimensional to three-dimensional structural transition of gold cluster Au 10 during soft landing on TiO 2 surface and its effect on CO oxidation

We investigate the possible structural transition of a planar Au10 cluster during its soft landing on a TiO2 (110) surface with or with no oxygen defects. The collision between the gold cluster and the oxide surface is simulated using the Car–Parrinello quantum molecular dynamics method. Both high-speed and low-speed conditions typically implemented in soft-landing experiments are simulated. It is found that under a high-speed condition, the gold cluster Au10 can undergo a sequence of structural transitions after colliding with a defect-free TiO2 (110) surface. When the TiO2 (110) surface possesses oxygen vacancies, however, chemical bonds can form between gold and Ti atoms if gold atoms contact directly with the vacancies. As a consequence, one oxygen vacancy is capable of trapping one Au atom, and thus can split the Au10 into two parts while bouncing back from the surface. In addition, we study reaction pathways for the CO oxidation based on three isomer structures of Au10 observed in the soft-landing simulation: (1) the precollision two-dimensional structure, (2) a postcollision three-dimensional (3D) structure, and (3) an intermediate (transient) 3D structure that appeared in the midst of the collision. This study allows us to examine the structure-activity relationship using the Au10 as a prototype model catalyst

Two-dimensional to three-dimensional structural transition of gold cluster Au 10 during soft landing on TiO 2 surface and its effect on CO oxidation

We investigate the possible structural transition of a planar Au10 cluster during its soft landing on a TiO2 (110) surface with or with no oxygen defects. The collision between the gold cluster and the oxide surface is simulated using the Car–Parrinello quantum molecular dynamics method. Both high-speed and low-speed conditions typically implemented in soft-landing experiments are simulated. It is found that under a high-speed condition, the gold cluster Au10 can undergo a sequence of structural transitions after colliding with a defect-free TiO2 (110) surface. When the TiO2 (110) surface possesses oxygen vacancies, however, chemical bonds can form between gold and Ti atoms if gold atoms contact directly with the vacancies. As a consequence, one oxygen vacancy is capable of trapping one Au atom, and thus can split the Au10 into two parts while bouncing back from the surface. In addition, we study reaction pathways for the CO oxidation based on three isomer structures of Au10 observed in the soft-landing simulation: (1) the precollision two-dimensional structure, (2) a postcollision three-dimensional (3D) structure, and (3) an intermediate (transient) 3D structure that appeared in the midst of the collision. This study allows us to examine the structure-activity relationship using the Au10 as a prototype model catalyst

The CDEX-1 1 kg Point-Contact Germanium Detector for Low Mass Dark Matter Searches

The CDEX Collaboration has been established for direct detection of light dark matter particles, using ultra-low energy threshold p-type point-contact germanium detectors, in China JinPing underground Laboratory (CJPL). The first 1 kg point-contact germanium detector with a sub-keV energy threshold has been tested in a passive shielding system located in CJPL. The outputs from both the point-contact p+ electrode and the outside n+ electrode make it possible to scan the lower energy range of less than 1 keV and at the same time to detect the higher energy range up to 3 MeV. The outputs from both p+ and n+ electrode may also provide a more powerful method for signal discrimination for dark matter experiment. Some key parameters, including energy resolution, dead time, decay times of internal X-rays, and system stability, have been tested and measured. The results show that the 1 kg point-contact germanium detector, together with its shielding system and electronics, can run smoothly with good performances. This detector system will be deployed for dark matter search experiments.Comment: 6 pages, 8 figure

An Updated Search of Steady TeV γ−\gamma-Ray Point Sources in Northern Hemisphere Using the Tibet Air Shower Array

Using the data taken from Tibet II High Density (HD) Array (1997 February-1999 September) and Tibet-III array (1999 November-2005 November), our previous northern sky survey for TeV $\gamma-$ray point sources has now been updated by a factor of 2.8 improved statistics. From $0.0^{\circ}$ to $60.0^{\circ}$ in declination (Dec) range, no new TeV $\gamma-$ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV $\gamma-$ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.Comment: This paper has been accepted by hepn