We propose a theoretical scheme for creating a two-dimensional Electromagnetically Induced Grating in a three-level $$\Lambda $$ Λ -type atomic system interacting with a weak probe field and two simultaneous position-dependent coupling fields—a two dimensional standing wave and an optical vortex beam. Upon derivation of the Maxwell wave equation, describing the dynamic response of the probe light in the atomic medium, we perform numerical calculations of the amplitude, phase modulations and Fraunhofer diffraction pattern of the probe field under different system parameters. We show that due to the azimuthal modulation of the Laguerre–Gaussian field, a two-dimensional asymmetric grating is observed, giving an increase of the zeroth and high orders of diffraction, thus transferring the probe energy to the high orders of direction. The asymmetry is especially seen in the case of combining a resonant probe with an off-resonant standing wave coupling and optical vortex fields. Unlike in previously reported asymmetric diffraction gratings for PT symmetric structures, the parity time symmetric structure is not necessary for the asymmetric diffraction grating presented here. The asymmetry is due to the constructive and destructive interference between the amplitude and phase modulations of the grating system, resulting in complete blocking of the diffracted photons at negative or positive angles, due to the coupling of the vortex beam. A detailed analysis of the probe field energy transfer to different orders of diffraction in the case of off-resonant standing wave coupling field proves the possibility of direct control over the performance of the grating.

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The method of stimulated Raman adiabatic passage is applied in order to coherently manipulate a three-level superconducting quantum interference device quantum bit with two microwave pulses. Simulations indicate that this method has the potential to allow for efficient control of the system for a wide range of pulse parameters. IntroductionIn the quest for practical systems for carrying out quantum computations [1], solid-state systems that make use of the Josephson effect are viable candidates [2]. This has been exhibited in a series of important experiments [3][4][5][6][7][8][9][10][11][12][13][14]. One particular scheme is based on magnetic flux states in superconducting quantum interference devices (SQUIDs) [2,[15][16][17][18][19][20][21][22][23][24][25][26]. In some of these schemes [2,[16][17][18][19], the SQUID quantum bit, or qubit, which is the basic element of a SQUID quantum computer, is based on a two-level system manipulated by external fields. The interaction of these systems with both classical [2,16,17] and quantized [18,19] fields has been analysed.Zhou et al.[20] have recently proposed a three-level Ã-type rf-SQUID qubit. Here, the states of the qubit are the two lower flux states j0i and j1i of the à system, and the manipulation of the qubit is done with two microwave fields that couple the lower states to an upper state jei. As the transition matrix elements corresponding to the transitions j0i $ jei and j1i $ jei are larger than that of the j0i $ j1i transition, the three-level SQUID qubit has been shown to be more favourable than the conventional two-level SQUID qubit for implementing a NOT gate. Amin et al. [21] have shown that the scheme of Zhou et al. is incomplete and have proposed an improved scheme for the rotation of a three-level SQUID qubit. More recently, Yang and Han [22] have addressed the same problem using far-off-resonant Raman coupling to achieve an arbitrary rotation of a three-level SQUID qubit. They have demonstrated that large detunings of the driving fields from the upper state could be favourable for

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We consider the problem of pulsed biexciton preparation in a quantum dot and show that a pulse-sequence with a simple on-off-on modulation can achieve complete preparation of the target state faster than the commonly used constant and hyperbolic secant pulses. The durations of the pulses composing the sequence are obtained from the solution of a transcendental equation. Furthermore, using numerical optimal control, we demonstrate that for a wide range of values of the maximum pulse amplitude, the proposed pulse-sequence prepares the biexciton state in the numerically obtained minimum time, for the specific system under consideration. We finally show with numerical simulations that, even in the presence of dissipation and dephasing, high levels of biexciton state fidelity can be generated in short times.

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We study the efficient preparation of the exciton state in a hybrid nanostructure composed by a semiconductor quantum dot and a metallic nanoparticle, when starting from the ground state, using pulses derived with the method of shortcuts to adiabaticity. We show with numerical simulations that high levels of exciton population can be obtained for a wide range of interparticle distances and for short pulse durations. This behavior appears also to be robust against small positioning errors of the system. The fidelity of the population inversion degrades for smaller distances and longer pulses, as the nonlinear terms in the equations, expressing the quantum dot–metal nanoparticle interaction, become stronger and affect the evolution for longer times. The present work is expected to help schemes toward the generation of single photons on demand or ultrafast nanoswitches, where the controlled population inversion in semiconductor quantum dots coupled to metal nanoparticles is an important task.