Inductive Algebras for Finite Heisenberg Groups

A characterization of the maximal abelian sub-algebras of matrix algebras that are normalized by the canonical representation of a finite Heisenberg group is given. Examples are constructed using a classification result for finite Heisenberg groups.Comment: 5 page

Steady state behaviour in atomic three-level lambda and ladder systems with incoherent population pumping

The steady state in three-level lambda and ladder systems is studied. It is well-known that in a lambda system this steady state is the coherent population trapping state, independent of the presence of spontaneous emission. In contrast, the steady state in a ladder system is in general not stable against radiative decay and exhibits a minimum in the population of the ground state. It is shown that incoherent population pumping destroys the stability of the coherent population trapping state in the lambda system and suppresses a previously discovered sharp dip in the steady state response. In the ladder system the observed minimum disappears in the presence of an incoherent pump on the upper transition.Comment: 4 pages, RevTex, 5 figures, to appear in Phys. Rev.

Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback

We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations

Tunable waveguide lattices with non-uniform parity-symmetric tunneling

We investigate the single-particle time evolution and two-particle quantum correlations in a one-dimensional $N$-site lattice with a site-dependent nearest neighbor tunneling function $t_\alpha(k)=t_0[k(N-k)]^{\alpha/2}$. Since the bandwidth and the energy levels spacings for such a lattice both depend upon $\alpha$, we show that the observable properties of a wavepacket, such as its spread and the relative phases of its constitutents, vary dramatically as $\alpha$ is varied from positive to negative values. We also find that the quantum correlations are exquisitely sensitive to the form of the tunneling function. Our results suggest that arrays of waveguides with position-dependent evanascent couplings will show rich dynamics with no counterpart in present-day, traditional systems.Comment: 5 pages, 4 figure

Simulation and Analysis of Biogas operated Double Effect GAX Absorption Refrigeration System

A thermodynamic simulation of a double effect generator heat exchanger absorption refrigeration cycle using biogas as source of energy has been carried out. The binary mixture considered in the present investigation was NH3 – H2O (Ammonia - Water). This simulation was performed in order to investigate the effect of the temperature and pressure of the high temperature generator and the pressure of evaporator have over the Coefficient of Performance (COP) for a constant condenser and absorber temperatures. The basic parameters at various state points of the cycle was computed using standard correlations. The solution circulation rates and volume of biogas required for operation of the cycle are analysed for the variations in operating parameters at the high temperature generator and evaporator

Carrier inversion noise has important influence on the dynamics of a semiconductor laser

We find that, although inversion noise has only a marginal effect on the linewidth of a semiconductor laser in continuous wave operation, in the presence of dynamics, it may play an important role in determining the final dynamical state. It is, therefore, essential to include realistic carrier noise when analysing semiconductor laser dynamics

Lasing without inversion in the absence of a coherent coupling field

We analyze the inversionless gain in a three-level ladder system by replacing the usual coherent coupling field with an incoherent field. Surprisingly, it is found that one can obtain inversionless amplification of a weak probe even in the absence of a coherent field in the model. We conclude that gain is determined by the ensemble average of the product of the two-photon coherence and the "effective Rabi frequency" of the field. Thus, even though the incoherent pump reduces the two-photon coherence, gain can be restored by choosing sufficiently high strengths of the incoherent field

Experimental and theoretical study of semiconductor laser dynamics due to filtered optical feedback

We report experimental results on the nonlinear dynamical response of a semiconductor laser subjected to time-delayed (>5 ns), frequency selective, optical feedback from a Fabry-Pe´rot interferometer type of filter. Three regimes of interest, based on the relative value of the filter bandwidth with respect to the relevant laser parameters (relaxation oscillation frequency and external cavity mode spacing), are identified, viz. a wide filter case, an intermediate filter width case, and a narrow filter case. The dynamical response of the laser is shown to be quite different in each of these regimes. The principal results are 1) the laser's linewidth enhancement factor, coupled with the nonlinear response of the filter, can be exploited to induce nonlinear dynamics in the instantaneous optical frequency of the laser light on a time scale related to the time-delay of the feedback, 2) a mode mismatch effect which arises from a detuning between the filter center frequency and the nearest external cavity mode and manifests itself in a reduction of the maximum light available for feedback, and 3) a reduction in, or even disappearance of, relaxation oscillations in the laser dynamics when a filter of appropriate width is chosen. More generally, it is observed that certain dynamics that occur due to unfiltered optical feedback may be suppressed when the feedback light is spectrally filtered