Coherent spinor dynamics in a spin-1 Bose condensate

Collisions in a thermal gas are perceived as random or incoherent as a consequence of the large numbers of initial and final quantum states accessible to the system. In a quantum gas, e.g. a Bose-Einstein condensate or a degenerate Fermi gas, the phase space accessible to low energy collisions is so restricted that collisions be-come coherent and reversible. Here, we report the observation of coherent spin-changing collisions in a gas of spin-1 bosons. Starting with condensates occupying two spin states, a condensate in the third spin state is coherently and reversibly created by atomic collisions. The observed dynamics are analogous to Josephson oscillations in weakly connected superconductors and represent a type of matter-wave four-wave mixing. The spin-dependent scattering length is determined from these oscillations to be -1.45(18) Bohr. Finally, we demonstrate coherent control of the evolution of the system by applying differential phase shifts to the spin states using magnetic fields.Comment: 19 pages, 3 figure

Silica Microspheres with Fibrous Shells: Synthesis and Application in HPLC

Monodispersed silica spheres with solid core and fibrous shell were successfully synthesized using a biphase reaction. Both the thickness and the pore size of the fibrous shell could be finely tuned by changing the stirring rate during synthesis. When stirring was adjusted from 0 to 800 rpm, the thickness of the shell could be tuned from 13 to 67 nm and the pore size from 5 to 16 nm. By continuously adjusting the stirring rate, fibrous shells with hierarchical pore structure ranged from 10 to 28 nm and thickness up to 200 nm could be obtained in one pot. We demonstrate that fibrous shells with controllable thickness and pore size could be coated on silica cores with diameters from 0.5 to 3 μm while maintaining the monodispersity of the particles. As a result of the unique fibrous structure, the BET surface area could reach ∼233 m² g^–1 even though the shell thickness was less than 150 nm. The core–shell particles were modified with C18, packed, and then used in high-performance liquid chromatography (HPLC) separation, showing separation performance as high as 2.25 × 10⁵ plates m^–1 for naphthalene and back pressure as low as 5.8 MPa. These silica microspheres with fibrous shells are expected to have great potential for practical applications in HPLC