Emmanuel Paspalakis

Electronic structure and nonlinear optical rectification in a quantum dot: effects of impurities and external electric field

The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process.

Spontaneous emission-induced coherent effects in absorption and dispersion of a V-type three-level atom

We study the effects of quantum interference from spontaneous emission in the creation of atomic coherence in a closed V-type system. We find that the absorption and dispersion properties of this atom can be significantly modified if this interference is optimized. Lasing with or without inversion, electromagnetically-induced transparency and enhancement of the index of refraction are all dependent on this interference.

Transparency near a photonic band edge

We study the absorption and dispersion properties of a

Fluorescence control through multiple interference mechanisms

{\bf \Lambda}

Coherent phenomena in photonic crystals

-type atom which decays spontaneously near the edge of a photonic band gap (PBG). Using an isotropic PBG model, we show that the atom can become transparent to a probe laser field, even when other dissipative channels are present. This transparency originates from the square root singularity of the density of modes of the PBG material at threshold.

Effects of spontaneous emission interference on population inversions of a V-type atom

We discuss the spontaneous emission from a coherently prepared and microwave-driven doublet of potentially closely spaced excited states to a common ground level. Multiple interference mechanisms are identified that may lead to fluorescence inhibition in well-separated regions of the spectrum or act jointly in canceling the spontaneous emission. In addition to phase-independent quantum interferences due to combined absorptions and emissions of driving field photons, we distinguish two competing phase-dependent interference mechanisms as means of controlling the fluorescence. The indistinguishable quantum paths may involve the spontaneous emission from the same state of the doublet, originating from the two different components of the initial coherent superposition. Alternatively the paths involve a different spontaneous photon from each of two decaying states, necessarily with the same polarization. This makes these photons indistinguishable in principle within the uncertainty of the two decay rates. The phase dependence arises for both mechanisms because the interfering paths differ by an unequal number of stimulated absorptions and emissions of the microwave field photons. @S1050-2947~98!03011-X#

Effects of probe field intensity in nonlinear optical processes in asymmetric semiconductor quantum dots

We study the spontaneous emission, absorption, and dispersion properties of a L-type atom where one transition interacts near resonantly with a double-band photonic crystal. Assuming an isotropic dispersion relation near the band edges, we show that two distinct coherent phenomena can occur. First the spontaneous emission spectrum of the adjacent free-space transition obtains ‘‘dark lines’’ ~zeros in the spectrum!. Second, the atom can become transparent to a probe laser field coupling to the adjacent free-space transition.

Arbitrary rotation and entanglement of flux SQUID qubits

Abstract The steady-state population behaviour in a laser driven V-type system has been analysed. The effects of spontaneous emission-induced coherence and of the relative phase of the two coherent driving fields are considered in detail. A large and unexpected population inversion is found on one of the optical transitions due to these coherent effects.

Rabi oscillations in a strongly driven semiconductor quantum well

We study nonlinear optical absorption and nonlinear optical rectification in an asymmetric semiconductor quantum dot structure under a strong probe field excitation. We apply a form of the rotating wave approximation for asymmetric quantum systems, solve the relevant density matrix equations under steady state conditions, and derive the formulae for nonlinear optical absorption and nonlinear optical rectification under the interaction with a strong probe field. The differences between our formulae and those of a previous study are also presented for the case of an electron confined in an asymmetric double quantum dot nanostructure.

The influence of density of modes on dark lines in spontaneous emission

We propose an approach for the arbitrary rotation of a three-level superconducting quantum interference device (SQUID) qubit and describe a strategy for the creation of coherence transfer and entangled states between two three-level SQUID quhits. The former is succeeded by exploring the coupled-uncoupled states of the system when irradiated with two microwave pulses, and the latter is succeeded by placing the SQUID qubits into a microwave cavity and used adiabatic passage methods for their manipulation.