Meson-baryon s-wave resonances with strangeness -3

Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian ( Phys. Rev. D 74, 034025 (2006)), we study the s-wave meson-baryon resonances in the strangeness S = - 3 and negative-parity sectors. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho-meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2⁺ octet of the nucleon and the 3/2⁺ decuplet of the Delta. Quantum numbers I(J ^P) = 0(3/2^-) are suggested for the experimental resonances Ω ^*(2250)^- and Ω ^*(2380)^-. Among other, resonances with I = 1 are found, which minimal quark content is sssˉl', being s the strange quark and l, l' any of the the light up or down quarks. A clear signal for such a pentaquark would be a baryonic resonance with strangeness -3 and electric charge -2 or 0, in proton charge units. We suggest looking for K ^- Ξ ^- resonances with masses around 2100 and 2240MeV in the sector 1(1/2^-), and for π ^± Ω ^- and K ^- Ξ ^*- resonances with masses around 2260MeV in the sector 1(3/2^-).     

Search for exotic baryons at HERMES

An experimental search for the Θ(1540)- and Λ(1520)-resonance was performed in quasi-real photoproduction on deuterium at the HERMES experiment. While evidence for Θ(1540) was found in the decay channel pK ⁰ _S→pπ ⁺ π ^-, no evidence for the corresponding anti-particle was found. In some models it is expected that the Θ(1540) and the Λ(1520) have similar production mechanisms. The photoproduction cross-sections for the Λ(1520) in the decay channel Λ(1520)→pK ^- and the corresponding anti-particle are determined. The partial photoproduction cross-sections for Λ(1520) and ˉ(1520) are obtained as σ _Λ(1520) = 65.3±8.8(stat)±6.9(syst)nb and σ _ˉ(1520) = 9.8±2.6(stat)±0.9(syst)nb, corresponding to a ratio R _Λ(1520) = σ _ˉ(1520)/σ _Λ(1520) = 0.15±0.05(stat)±0.02(syst).     

Raising and Lowering of Generalized Hulthén Potential from Supersymmetry Approaches

We obtain the exact bound states of the generalized of Hulthén potential with negative energy levels using an analytic approach. In order to obtain bound states, we use the associated Jacobi differential equation. Using the supersymmetry approach to quantum mechanics, we show that these bound states, via four pairs of first order differential operators, represent four types of ladder equations. Two types of these supersymmetric structures suggest derivation of algebric solutions for the bound states using two different approaches. PACS 21.60.Cs; 21.60.Fw; 21.60.-n; 03.65.Fd; 03.65.Ge; 03.65.-w     

Electronic structure of spin-chain compounds: common features

The incommensurate composite systems M₁₄Cu₂₄O₄₁ (M = Ca, Sr, La) are based on two fundamental structural units: CuO₂ chains and Cu₂O₃ ladders. We present electronic structure calculations within density functional theory in order to address the interrelations between chains and ladders. The calculations account for the details of the crystal structure by means of a unit cell comprising 10 chain and 7 ladder units. It turns out that chains and ladders can be treated independently, which allows us to introduce a model system based on a reduced unit cell. For the CuO₂ chains, we find two characteristic bands at the Fermi energy. Tight binding fits yield nearest and next-nearest neighbour interactions of the same order of magnitude.     

双势垒磁性隧道结中量子阱共振隧穿效应的第一性原理理论

磁性隧道结材料中自旋相关的量子阱态所导致的共振隧穿现象具有很重要的研究和应用价值，文章介绍了最近在Fe（001）／MgO／Fe／MgO／Fe双势垒磁性隧道结中存在的量子阱共振隧穿效应的理论研究工作，通过量子阱态的第一性原理的计算以及结合对中间Fe薄膜孤岛结构所导致Coulomb阻塞效应的分析，证实了最近Nozaki等人（Nozaki T et al．Phys．Rev．Lett．，2006，96：027208）实验中得到的振荡效应确实来源于中间Fe层多数自旋电子在Г点处形成的△1对称性的量子阱态．Coulomb阻塞效应的存在正是导致实验中低温下量子阱共振隧穿效应不够明显的主要原因．     

通过Raman相互作用制备三个腔场的W型纠缠相干态

通过对比分立变量量子信息过程和连续变量量子信息过程的差别,利用相干态比较容易获得的这个特点,提出一种方案制备三个腔场的W型纠缠相干态.方案基于Λ型三能级原子与单模腔场的简并Raman 相互作用.三个相同的腔初始分别处于相干态,三个相同的原子初始处于W型纠缠态,通过三个原子分别与三个腔的Raman相互作用、选择适当的相互作用时间并探测作用后的三个原子,三个腔场坍缩为W型纠缠相干态.在原子与腔的相互作用过程中原子不处于高能级,可以忽略原子的自发辐射,系统的相干性能够得到较好的维持.基于当前的腔量子电动力学技术,相信方案能在实验上实现.该方案制备的三个腔场W型纠缠相干态有望在连续变量量子信息过程中有重要的应用价值.文中将方案推广到制备n(n〉3)个腔场的W型纠缠相干态.     

双模纠缠相干光与Bell态原子系统的光子统计

运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的光子统计性质.分析了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对双模光场的光子统计性质的影响.结果表明：双原子体系的初态为｜β00〉、｜β10〉时,光场在其演化过程中不出现光子的反聚束效应；而当原子初态为｜β01〉或｜β11〉时,在一定的条件下可出现光子的反聚束效应.并且在光场的演化过程中,光子的反聚束效应出现的次数、时间和深度极其敏感地依赖于初始光场的平均光子数,而受到双模纠缠光场的纠缠程度以及双原子间偶极作用强度的影响很微弱.     

与色散介质毗邻的一维半无限光子晶体表面态

运用Bloch定理和传输矩阵方法,研究了与色散介质毗邻的由两种材料组成的半无限一维光子晶体局域表面态的电场和色散关系.和以空气为背景的一维光子晶体相比,毗邻色散介质的光子晶体表面模色散曲线在一定堆积次序下会在较低的带隙中发生断开,较高带隙中的表面模群速度在不同堆积次序下会有很大差异.当与色散介质毗邻的物质折射率较大时,较高带隙中的表面模群速度较小；与色散介质毗邻的物质折射率较小时,较高带隙中表面模的群速度较大.     

Kinetic energy release for the collision-induced dissociation of CO<Superscript>+</Superscript>

The kinetic energy release distributions (KERDs) of C⁺ and O⁺ fragments arising from 5 keV collision-induced dissociation (CID) of CO⁺ ions with helium have been measured. The KERDs of C⁺ and O⁺ exhibit different features corresponding to the states that participate in CID processes. We have identified groups of dissociative and predissociative states, and compare them with theoretical and experimental values.