The effects of indium segregation on exciton binding energy and oscillator strength in GaInAs/GaAs quantum wells

We solve analytically the Schrödinger equation taking into account the shape changes of GaInAs/GaAs quantum wells due to indium segregation during the MBE growth by using transfer matrix method. The indium compositional profiles of the quantum wells are provided using the phenomenological model. The fundamental transition energy, binding energy and oscillator strength of excitons as a function of indium segregation coefficient R$R$ and well width are studied. For narrow wells (less than 40 ML), the exciton binding energy and oscillator strength decrease, but for wide wells (larger than 40 ML), increase with increasing the segregation coefficient R$R$. It is shown that indium segregation degrades the optical properties and results in a blue-shift of exciton transition energy in GaInAs/GaAs quantum wells.     

Quantum-classical correspondence for motion on a plane with deficit angle

A particle constrained to move on a cone and bound to its tip by harmonic oscillator and Coulomb-Kepler potentials is considered both in the classical as well as in the quantum formulations. The SU(2) coherent states are formally derived for the former model and used for showing some relations between closed classical orbits and quantum probability densities. Similar relations are shown for the Coulomb-Kepler problem. In both cases a perfect localization of the densities on the classical solutions is obtained even for low values of quantum numbers.     

Synthesis and optical characterization of vertically grown ZnO nanowires in high crystallinity through vapor-liquid-solid growth mechanism

The gas-phase growth and optical characteristics of 1-dimensional ZnO nanostructure have been investigated. The ZnO nanowires (NWs) were grown vertically on Au coated silicon substrates by vapor-liquid-solid (VLS) growth mechanism using chemical vapor deposition (CVD). The ZnO NWs were grown in the crystal direction of [0 0 0 1]. The ZnO NWs exhibit the uniform size of less than 100 nm in diameter and up to 5 μm in length. Photoluminescence (PL) spectrum of ZnO NWs shows the strong band-edge emission at ∼380 nm (∼3.27 eV) without significant deep-level defect emission. The exciton lifetime of ZnO NWs was measured to be approximately 150 ± 10 ps.     

Generalized structure of higher order nonclassicality

A generalized notion of higher order nonclassicality (in terms of higher order moments) is introduced. Under this generalized framework of higher order nonclassicality, conditions of higher order squeezing and higher order subpoissonian photon statistics are derived. A simpler form of the Hong-Mandel higher order squeezing criterion is derived under this framework by using an operator ordering theorem introduced by us in [A. Pathak, J. Phys. A 33 (2000) 5607]. It is also generalized for multi-photon Bose operators of Brandt and Greenberg. Similarly, condition for higher order subpoissonian photon statistics is derived by normal ordering of higher powers of number operator. Further, with the help of simple density matrices, it is shown that the higher order antibunching (HOA) and higher order subpoissonian photon statistics (HOSPS) are not the manifestation of the same phenomenon and consequently it is incorrect to use the condition of HOA as a test of HOSPS. It is also shown that the HOA and HOSPS may exist even in absence of the corresponding lower order phenomenon. Binomial state, nonlinear first order excited squeezed state (NLESS) and nonlinear vacuum squeezed state (NLVSS) are used as examples of quantum state and it is shown that these states may show higher order nonclassical characteristics. It is observed that the Binomial state which is always antibunched, is not always higher order squeezed and NLVSS which shows higher order squeezing does not show HOSPS and HOA. The opposite is observed in NLESS and consequently it is established that the HOSPS and HOS are two independent signatures of higher order nonclassicality.     

Schemes to generate and distinguish a type of genuine four-qubit entangled states in a cavity QED system

We propose a scheme to generate a type of genuine four-qubit entangled states, which were firstly introduced by Yeo et al. [Y. Yeo, W. K. Chua, Phys. Rev. Lett. 96 (2006) 060502]. These states have many interesting entanglement properties and possess possible applications in quantum information processing and in fundamental tests of quantum physics. We show that such a type of 16 orthonormal basis states can be deterministically distinguished by a cavity QED system.     

Interaction of bathocuproine with metals (Ca, Mg, Al, Ag, and Au) studied by density functional theory

Electronic structure of the interface between a bathocuproine (BCP) molecule and metal surface was studied by density functional theory. The bond energy of BCP with metal surface increased with decreasing work function of metals, that is, Au, Ag, Al, Mg, and Ca in this order. The charge transfer also increased with decreasing metal work function. It was analyzed that the Fermi level and the lowest unoccupied molecular orbital of BCP are composed of both BCP and metal orbital component, and electron transport properties across the BCP and metal is discussed based on these analyses.     

Book reviews

MODERN CRYSTALLOGRAPHY I, by B. K. Vainshtein, Springer Series in Solid State Sciences 15. Springer-Verlag, New York, 1981. 399 pp., USf47.50.

SPECTROSCOPY IN CHEMISTRY AND PHYSICS: Modern Trends, Edited by F. J. Comes, A. Muller and W. J. Orville-Thomas (Elsevier Scientific Publishing Company). Price US $87.75, Dfl 180.00.

ELECTRONIC STATES OF MOLECULES AND ATOM CLUSTERS-Foundations and Prospects of Semiempirical Methods, by G. Del Re, G. Berthier and J. Serre. Springer Lecture Notes in Chemistry, Vol. 13. Price: US817.50 (Springer-Verlag, Berlin, 1980).

MATERIALS FOR THE FUTURE, Edited by P. M. Kelly, Australian Academy of Science, 1981.     

One-body and Two-body Fractional Parentage Coefficients for Spinor Bose-Einstein Condensation

A very effective tool, namely, the analytical expression of the fractional parentage coefficients (FPC), is introduced in this paper to deal with the total spin states of N-body spinor bosonic systems, where N is supposed to be large and the spin of each boson is one. In particular, the analytical forms of the one-body and two-body FPC for the total spin states with {N} and {N−1,1} permutation symmetries have been derived. These coefficients facilitate greatly the calculation of related matrix elements, and they can be used even in the case of N→∞. They appear as a powerful tool for the establishment of an improved theory of spinor Bose-Einstein condensation, where the eigenstates have the total spin S and its Z-component being both conserved.     

Three-party quantum secret sharing of secure direct communication based on x-type entangled states

Based on x-type entangled states and the two-step protocol [Deng F G, Long G L and Liu X S 2003 Phys. Rev. A 68 042317], a quantum secret sharing protocol of secure direct communication based on x-type entangled states ｜X00〉3214 is proposed. Using some interesting entanglement properties of this state, the agent entirety can directly obtain the secret message from the message sender only if they collaborate together. The security of the scheme is also discussed.