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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.

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In this work we study the potential for coherent manipulation of an asymmetric double quantum dot structure by the use of adiabatic methods. These methods are the Stimulated Raman Adiabatic Passage (STIRAP) and its modification the fractional STIRAP. We show that such a method can be used for complete electron transfer between the two lower states of the quantum dots. In addition, with fractional STIRAP a coherent superposition of the two lower states of the quantum dots can be created.1 Introduction The interaction of electrons confined in double quantum dot structures with electromagnetic driving fields has attracted much attention in the past decade [1][2][3][4]. Several interesting phenomena have been recognized when the quantum dot structure contains one or two electrons. Examples include controlled transfer of electrons between the two quantum dots [1,3] and creation of maximally entangled states in two-electron quantum dot systems [2,4]. These effects are of central interest in the topical area of quantum computation as quantum dots are artificially created structures with potential scalability, so they are one of the most important candidates for realizing solid state quantum computation.In this work we study the potential for coherent manipulation of an asymmetric double quantum dot structure [3,4] by the use of adiabatic methods. These methods are the Stimulated Raman Adiabatic Passage (STIRAP) [5] and its modification the fractional STIRAP [6]. In STIRAP two electromagnetic pulses are applied in the quantum dot structure in a counter-intuitive sequence [5]. These pulses are also partially overlapping. We show that such a method can be used for complete electron transfer between the two lower levels of the quantum dots. In fractional STIRAP, in addition to the previous procedure, the pulses are also switched-off simultaneously [6]. In this case a coherent superposition of the two lower levels of the quantum dots can be created. We note that several studies in the past five years have applied STIRAP and fractional STIRAP for the control of the dynamics of semiconductor nanostructures [7]. The results of the present paper is a direct application of STIRAP in a double quantum dot structure. The results of this paper can be also directly applied to the asymmetric quantum dot structures of Ref. [3].

We study the creation of high-efficiency controlled population transfer in intersubband transitions of semiconductor quantum wells. We give emphasis to the case of interaction of the semiconductor quantum well with electromagnetic pulses with a duration of few cycles and even a single cycle. We numerically solve the effective nonlinear Bloch equations for a specific double GaAs/AlGaAs quantum well structure, taking into account the ultrashort nature of the applied field, and show that high-efficiency population inversion is possible for specific pulse areas. The dependence of the efficiency of population transfer on the electron sheet density and the carrier envelope phase of the pulse is also explored. For electromagnetic pulses with a duration of several cycles, we find that the change in the electron sheet density leads to a very different response of the population in the two subbands to pulse area. However, for pulses with a duration equal to or shorter than 3 cycles, we show that efficient population transfer between the two subbands is possible, independent of the value of electron sheet density, if the pulse area is Π.