International Journal of Modern Physics B

We review some recent results on discrete symmetries and topological order in spinor Bose–Einstein condensates (BECs) of ²³Na. For spin one bosons with two-body scatterings dominated by a total spin equal to two channel, the BECs are in quantum spin nematic states at a low density limit. We study spin correlations in condensates at different limits and analyze hidden symmetries using a non-perturbative approach developed recently. Furthermore we investigate the influence of hidden Z₂ symmetries and U(1) quantum orders in symmetry partially restored states, particularly the effects on topological excitations.

We consider a single-Cooper-pair box biased by a classical voltage and also irradiated by a single-mode quantized field. We assume that the box is initially in a mixed state, and investigate the quantum dynamics of the Cooper-pair box and show that the collapse and revival phenomenon can exist in this system. We also study the quantum entropy of the single-Cooper-pair box and discuss the effects of the different parameters on this quantum entropy. We find that the box, which is initially in a mixed state, may evolve into an almost pure state.

A V-type three level system with two closely spaced upper levels interacting with a single mode of the electromagnetic field is studied for the absorptive and dispersive lineshapes. A semiclassical description for the atom-field interaction is being adopted to obtain the usual optical Bloch equations. The approximate analytical solutions for the density matrix elements are obtained by solving coupled optical Bloch equations. Through the off-diagonal density matrix elements, the introduction of phase angles between the levels participating in dipole allowed transitions are automatic. It is shown that these phases are appreciable if the applied electromagnetic field is strong. These field dependent phases (coherence) are responsible for the reduction of the inversionless gain and the absorptionless dispersion. For large decay constants, it is found that the energy gap between the upper two levels has no role to play on the laser without inversion and on the absorptionless dispersion. However, for large population per unit decay, a significant increase of the absorptionless dispersion and the inversionless gain is obtained. The condition for large population decay and a possible experimental realization of the field dependent phases are discussed.

We generalize a study of the behavior of a three-level atom in a single-mode mazer. Our formulation takes into account the interaction region and the spatial variation along the cavity axis. A general analytic time-dependent solution is obtained, and some special cases reduce to very simple expressions. When propagation effects are taken into consideration, the emission probability is influenced significantly. We provide the necessary arguments to justify the validity of our conclusions for emission probability and micromaser whose dynamics is governed by the wave function. Our main conclusion is that in the present system, the inclusion of the spatial dependence of the cavity region is necessary and important. We provide numerous examples to illustrate this correspondence, and provide evidence of its usefulness.

Spectroscopic and Langmuir probe measurements are presented to characterize the argon glow discharge plasma generated by a cost-effective 50 Hz AC power source. Optical emission spectra (400–700 nm) are recorded for different gas flow rates and filling pressures at constant power level. The plasma parameters (electron temperature and density) are deduced from the relative intensities of Ar-I and Ar-II lines. The variation in the intensity ratio of the selected emission lines, electron temperature and density is studied as a function of gas flow rate and filling pressure. Slight increase in the intensity ratio I₂(426.62 nm)/I₁(404.44 nm) of the emission lines is observed whereas the electron temperature and density are found to decrease with increase in gas flow rate and filling pressure.

The ground state of the spiked harmonic oscillator with the potential has been obtained variationally for α < 3 and recently by a numerical procedure for α > 3. Due to the Klauder phenomemon at α = 3, analytic techniques do not smoothly interpolate between α < 3 and α > 3. Here we use the N^-1 expansion, where N is the dimensionality of space, to set up an analytic scheme that can be continued across α = 3.

The effect of temperature on the emulsification has been investigated by discontinuous molecular dynamic simulation. When a large oil drop is put in water, on one hand the mixing entropy makes it divide into small oil drops; on the other hand the interactions among particles drives the small oil drops fowards aggregation. The evolution of the mean size of oil drops obeys the exponential delay law. There exist an active temperature, at which, the addition of surfactants has obvious effect on the emulsification. The surfactants with low HLB value (e.g. H₁T₃) make the dispersity of emulsion decrease, and the surfactants with high HLB value (e.g. H₂T₂ and H₃T₁) make a contribution to increase the dispersity of emulsion.

A laboratory ultrasound technique has been developed to measure the longitudinal velocity of sound in high purity and density boron carbide and lanthanum hexaboride materials prepared by shock wave compression. Using the measured value of the longitudinal velocity of sound υ_L, we have calculated the Young's modulus E, the Bulk modulus K, the Shear modulus G and the Poisson's ratio ν. X-rays diffraction has also been carried out on these materials.