Levente Horvath

We introduce the concept of initial-phase spectroscopy as a control of the dynamics of entangled states encoded into a two-atom system interacting with a broadband squeezed vacuum field. We illustrate our considerations by examining the transient spectrum of the field emitted by two systems, the small sample (Dicke) and the spatially extended (non-Dicke) models. It is found that the shape of the spectral components depends crucially on the relative phase between the initial entangled state and the squeezed field. We follow the temporal evolution of the spectrum and show that depending on the relative phase a hole burning can occur in one of the two spectral lines. We compare the transient behavior of the spectrum with the time evolution of the initial entanglement and find that the hole burning can be interpreted as a manifestation of the phenomenon of entanglement sudden death. In addition, we find that in the case of the non-Dicke model, the collective damping rate may act like an...

We study collective spontaneous emission from arbitrary distributions of N two-state atoms using quantum trajectory theory and without an a priori single-mode assumption. Assuming a fully excited initial state, we calculate the angular distribution of the average integrated intensity. We investigate the dependence of the angular distribution of emission on the geometry of the atomic distribution. The formalism is developed around an unravelling of the master equation in terms of source mode quantum jumps. A modified boson approximation is made to treat the many-atom case, where it is found that strong directional superradiance occurs for a few hundred to a few thousand atoms. In order to illustrate important differences between our model and single-mode models we consider shot-to-shot intensity fluctuations and angular correlations in the emitted intensity.

ABSTRACT Using master equation and quantum Monte Carlo wavefunction approaches, we study the circumstances surrounding the emergence and degradation of the elusive squeezing of fluctuations in two-level atom resonance fluorescence. For its measurement we suggest conditional homodyne detection (CHD) [G.T. Foster, L.A. Orozco, H.M. Castro-Beltran, H.J. Carmichael, Phys. Rev. Lett. 85, pp. 3149-3152, 2000], which is nearly independent of detector efficiencies, which have harmed previous attemps. Squeezing in resonance fluorescence requires a weak laser, so the average interval between emitted photons is much longer than the regression time to the steady state; here, the spectrum of the out-of-phase quadrature is a negative peak. In CHD, moderate fields generate a non-zero third-order correlation in the dipole fluctuations that contaminates squeezing, making the noise non- Gaussian. If the probability to emit two and even three close photons is still small the additional contribution is also negative, helping to make the full spectrum a bit larger and easier to measure. Strong driving spreads the photoemission distribution, which destroys squeezing, and the third order fluctuations become responsible for the non-classicality of the fluorescence.

ABSTRACT The quadrature fluctuations of the fluorescence of the weak transition of a bichromatically driven V-type three-level atom are shown to be asymmetric and giant under conditional homodyne detection, signaling non-Gaussian fluctuations.

ABSTRACT Every minute of every day, each of us encounters and must negotiate constraints. Whether they are the speed limits on the highways to work, or the time when we must be at work, constraints are unavoidable. Constraints have special importance for creative activity, in that they police the boundaries within which problem-solving tasks are conducted [10]. In doing so, constraints help individuals avoid the fruitless pursuit of solutions unlikely to succeed. But constraints applied without consideration of unique problem context and of the skills of individuals can also act as a straitjacket. Within software and systems design, constraints play an important role in guiding the development of products. Often incorporated as part of development methodology, constraints limit design space in order to guide designers toward good solutions. But constraints specified by methodology are rarely followed religiously [12]. Designers tend rather to modify methodologies to suit their preferences, abilities, and circumstances. Designers may lack this freedom, however, when a CASE tool is used to support systems development. CASE tools have the ability to enforce methodological constraints, making it difficult for designers to ignore or circumvent them. This can be a great benefit, ensuring that designs conform to a development methodology, and to notation standards. However, it may also frustrate designers, who may relegate CASE tool use to simple design capture rather than creative design development. Our premise is that CASE tool constraints significantly affect how software designers work, in turn affecting product quality and user productivity. In order to test this premise, a more thorough understanding of the nature of constraints is needed. This article contributes to that understanding by proposing a taxonomy that may be used to evaluate user responses to CASE constraints. Our ultimate goal is to facilitate the improved implementation of constraints in CASE tools. We believe one reason CASE tools are not used as extensively as had been expected [5] is that their implementation of constraints is arbitrary. The tools are not

We study collective spontaneous emission from arbitrary distributions of N two-state atoms using quantum trajectory theory and without an a priori single-mode assumption. Assuming a fully excited initial state, we calculate the angular distribution of the average integrated intensity. We investigate the dependence of the angular distribution of emission on the geometry of the atomic distribution. The formalism is developed around an unravelling of the master equation in terms of source mode quantum jumps. A modified boson approximation is made to treat the many-atom case, where it is found that strong directional superradiance occurs for a few hundred to a few thousand atoms. In order to illustrate important differences between our model and single-mode models we consider shot-to-shot intensity fluctuations and angular correlations in the emitted intensity.

Electromagnetic bandgap (EBG) materials, also known as photonic crystals, can provide significant advantages for suppressing and directing radiation when used in antennas. Thus far, most research has focussed on two-dimensional EBG materials because they are easier to build, but three-dimensional EBG materials have the potential to provide greater control of the radiation properties of antennas due to their complete bandgap.

We study collective spontaneous emission from arbitrary distributions of N two-state atoms using quantum trajectory theory and without an a priori single-mode assumption. Assuming a fully excited initial state, we calculate the angular distribution of the average intensity, focusing on pencil-and disc-shaped samples. The formalism is developed around an unravelling of the master equation in terms of source mode quantum

... Technol. Lett., vol. 22, no. 2, pp. 136–139, Jul. 1999. [23] C. Cheype, C. Serier, M. Thèvenot,T. Monédière, A. Reineix, and B. Jecko, “An electromagnetic bandgap resonator antenna,” IEEE Trans. Antennas Propag., vol. 50, no. 9, pp. 1285–1290, Sep. 2002. ...