On the energy-dependent number of electronic states in a quantum-well laser diode under a perpendicular magnetic field

The number of electronic states in a quantum-well laser diode under a perpendicular, uniform and time-independent magnetic field is considered as a function of the electronic energy. Within this framework, the energy-averaged number of states is calculated over a suitable energy range. In particular, an expression for the above average number is given when the magnetic field is relatively weak and the devices are assumed to be quasi-one-dimensional.     

Three qubits in a symmetric environment: Dissipatively generated asymptotic entanglement

We study the asymptotic entanglement of three identical qubits under the action of a Markovian open system dynamics that does not distinguish them. We show that by adding a completely depolarized qubit to a special class of two-qubit states, by letting them reach the asymptotic state and by finally eliminating the added qubit, can provide more entanglement than by direct immersion of the two qubits within the same environment.     

The use of balanced homodyne and squeezed states for detecting weak optical signals in a Michelson interferometer

The possibility of using squeezed states and balanced homodyne detection of optical signals in a Michelson interferometer is discussed. The present analysis describes photon statistics measurements effects related to quadrature balanced homodyne detection showing the advantage of using this scheme for detecting weak optical signals.     

Impact of chain architecture (branching) on the thermal and mechanical behavior of polystyrene thin films

The modulus and glass transition temperature (T_g) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) T_g for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in T_g. There are subtle differences between the architectures with reductions in T_g for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ～40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

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.     

On the cut‐off phenomenon for the transitivity of randomly generated subgroups

Consider K ≥ 2 independent copies of the random walk on the symmetric group S_N starting from the identity and generated by the products of either independent uniform transpositions or independent uniform neighbor transpositions. At any time $n\in \mathbb{N}$, let G_n be the subgroup of S_N generated by the K positions of the chains. In the uniform transposition model, we prove that there is a cut‐off phenomenon at time N ln(N)/(2K) for the non‐existence of fixed point of G_n and for the transitivity of G_n, thus showing that these properties occur before the chains have reached equilibrium. In the uniform neighbor transposition model, a transition for the non‐existence of a fixed point of G_n appears at time of order $N^{1+\frac{2}{K}}$ (at least for K ≥ 3), but there is no cut‐off phenomenon. In the latter model, we recover a cut‐off phenomenon for the non‐existence of a fixed point at a time proportional to N by allowing the number K to be proportional to ln(N). The main tools of the proofs are spectral analysis and coupling techniques. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2012     

On the simulation by a magnetic field of the quantized states in a quantum-well laser diode

The quantized states in a quantum-well semiconductor laser are simulated analytically by a magnetic field perpendicular to the well (infinite quasi-one-dimensional potential well) by deriving a close relationship for the magnetic-field strength which becomes a discrete quantity.     

pH reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

In this work, we prepared a tertiary amide-based gemini surfactant (DSTAPA), which contained two pH-sensitive tertiary amide head groups. Then the molecule state distribution and self-assembly transition of the surfactant in aqueous solution were investigated under different pH conditions. The DSTAPA molecules were on the states of double cationic (DSTAPAH²⁺), single cationic (DSTAPAH⁺), and double tertiary amine groups (DSTAPA) under acidic, neutral, and basic conditions, respectively. With the variation of the molecule states, the sample was water-like below pH of 6.8 and immediately transformed to gel-like fluid between pH of 6.8 and 7.8, then changed to white precipitate with the further increase of pH value. Furthermore, the microstructure and regulation mechanism were investigated by rheological measurements, dynamic light scattering, and cryogenic transmission electron microscopy. The appearance and micelle transitions of the DSTAPA aqueous solution are actually owing to the spherical–worm-like micelle transition, leading to dramatic viscosity increase and hydrogel formation. This transition was completely reversible and repeated for at least three cycles. Finally, a reasonable mechanism of the transition was proposed based on the viewpoints of the molecular states and micelle structures. The DSTAPA aqueous system with pH-reversible property has a great potential application in oil and gas production.