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Adiabatic Concentration and Coherent Control in Nanoplasmonic Waveguides
Published in Sergey I Bozhevolnyi, Plasmonic, 2019
We have proposed15 a principally different approach to ultrafast optical control on the nanoscale based on the general idea of coherent control. The coherent control of the quantum state of atom and molecules is based on the directed interference of the different quantum pathways of the optical excitation,16–25 which is carried out by properly defining the phases of the corresponding excitation waves. This coherent control can also be imposed by an appropriate phase modulation of the excitation ultrashort (femtosecond) pulse.22,26–28 Shaping the polarization of a femtosecond pulse has proven to be a useful tool in controlling quantum systems.29
Nonlinear Dynamics in Quantum Photonic Structures
Published in Joachim Piprek, Handbook of Optoelectronic Device Modeling and Simulation, 2017
Gabriela Slavcheva, Mirella Koleva
Quantum coherent control represents a universal approach for predictable manipulation of the properties of quantum systems, such as atoms and molecules. This technique has most recently been applied to QD solid-state systems. Coherent control in semiconductor nanostructures allows for coherent manipulation of the carrier wavefunctions on a time scale shorter than typical dephasing times. This is a prerequisite for successful implementation of ultrafast optical switching and quantum information processing. Quantum coherent control requires use of ultrashort pulses considerably shorter than the characteristic relaxation times in matter (τ≪T1,T2). This is equivalent to the photon-dipole coupling rate exceeding all dissipative rates in the system, a general condition for achieving the strong-coupling regime. The ultrashort pulses are usually characterized by high field amplitudes and, consequently, lead to nonlinear optical effects, such as coherent pulse propagation and self-induced transparency (SIT) [17]. The phenomenon of SIT is observable above a critical power threshold for a given pulse width: a high-intensity, ultrashort pulse propagating through a medium composed of an ensemble of resonant quantum two-level absorbers, whose relaxation times greatly exceed the pulse duration, travels at a reduced speed and unchanged shape with anomalously low energy loss. The absorbers are driven into the excited state by absorbing ultrashort pulse energy; by reradiating this energy into the pulse, they return to the ground state. Thus, the optical energy is carried through the medium not by the electromagnetic field, but by a coupled light-matter polariton wave. The polariton is a mixed light-matter quasiparticle resulting from the strong coupling of the optical wave to the medium's polarization. As a result, the pulse travels as a solitary wave, known as a SIT-soliton. This soliton is localized both in space and time, in contrast with the well-known nonlinear optics solitons which result from the interplay between nonlinearity and the medium's dispersion and/or diffraction. The condition of SIT is predicted by the remarkable pulse-area theorem (PAT) [18] which establishes a general criterion for stable, ultrashort pulse propagation in attenuating or amplifying media based on an integral quantity—namely, the pulse area. This phenomenon can be preserved to a great extent in solid-state systems—e.g., semiconductors—and has been experimentally demonstrated by picosecond pulse propagation in QD waveguides [19].
Phase control in coherent population distribution in molecules
Published in Journal of Modern Optics, 2018
We recently witnessed a lot of interest in the coherent laser control of atomic and molecular processes (1,2). Two-pathway interference between same initial level and final level is one of the most practical methods to achieve this control (2,3). One of the means of this coherent control is phase control, in which optical phases are introduced into coherent laser-matter interactions in order to manipulate quantum interference effects and thus to achieve targeted result. The control of unimolecular photo dissociation product yield by varying the relative phase and the amplitude of two simultaneously applied laser fields of frequencies ω1 and ω3 = 3ω1 was introduced by M. Shapiro and Paul Brumer (3). Two-pathway coherent control of photo ionization and photo dissociation had attracted much attention during the past two decades employing the first and third harmonics (ω1 and ω3 = 3ω1), as well as other schemes with either both odd or both even numbers of photons participating in the two pathways. On the other hand, interference between the absorption amplitudes for even and odd numbers of photons, e.g. in ω1 and ω2 = 2ω1 photo ionization or photo dissociation, does not contribute to the total yields. In this case, angle-resolved photo fragment distribution was observed. The first phase dependent experiment by Chen et al. (4) was successfully reported in which total ionization was modulated through interference of ω1 and ω3 = 3ω1 excitation in mercury. In an experiment by Muller et al. (5) using ω1 and ω2 = 2ω1, phase-dependent ATI photo fragment spectra was reported. Theoretical studies on coherent radiative control of IBr photo dissociation via simultaneous ω1 and ω3 = 3ω1 excitations was done by Chan et al. (6). Gordon et al. used two laser beams of ω1 and ω3 = 3ω1 to excite HCl (7) and HI molecule (8) to the ionization or dissociation continua. By varying the phase difference between the two beams, they were able to favour one reaction product over other. Several other theoretical (9–12) and experimental works (13,14) involving fundamental frequency and its third harmonic to demonstrate phase control quantum interference had also been reported in the literature.