Multicolor Pulses Research Articles

GaN quantum dot based quantum information/computation processing

In this paper we propose to use GaN quantum dots (QDs) as building blocks for solid state quantum computing devices. The existence of a strong built-in electric field induced by the spontaneous polarization and by the piezoelectricity is exploited to entangle few-exciton states in coupled QDs without the use of external fields. The analysis of the electro-optical response of the coupled GaN QDs is based on a realistic—i.e. fully tri-dimensional—description of Coulomb-correlated few-electron states, obtained via a direct-diagonalization approach. The combined effect of the built-in electric field and ultrafast sequences of multicolor laser pulses in the few-carrier regime is investigated. We show how the built-in field induces intrinsic dipole–dipole coupling and thus allows the implementation of quantum information processing. As an example we will implement basic quantum information gates and we will demonstrate that our implementation scheme is compatible with a sub-picosecond operation timescale, i.e. with timescales much lower than the decoherence time of the system.

All-optical quantum dot implementation for quantum computing

We present an all-optical scheme for a solid-state implementation of quantum information processing. The combined effect of static electric fields and ultrafast sequences of multi-color laser pulses on a semiconductor quantum dot array is investigated. We show how these ingredients can be used to perform single- as well as two-qubit gate operations, by exploiting the ground-state excitonic transitions as computational degrees of freedom. We demonstrate that by these means it is possible to implement basic quantum-computation operations on a time scale much shorter than the exciton dephasing time.

Electro-optical properties of semiconductor quantum dots: Application to quantum information processing

A detailed analysis of the electro-optical response of single as well as coupled semiconductor quantum dots is presented. This is based on a realistic ---i.e., fully tridimensional--- description of Coulomb-correlated few-electron states, obtained via a direct-diagonalization approach. More specifically, we investigate the combined effect of static electric fields and ultrafast sequences of multicolor laser pulses in the few-carrier, i.e., low-excitation, regime. In particular, we show how the presence of a properly tailored static field may give rise to significant electron-hole charge separation; these field-induced dipoles, in turn, may introduce relevant exciton-exciton couplings, which are found to induce significant ---both intra- and inter-dot--- biexcitonic splittings. We finally show that such few-exciton systems constitute an ideal semiconductor-based hardware for an all optical implementation of quantum information processing.

Intrinsic dipole–dipole excitonic coupling in GaN quantum dots: application to quantum information processing

We propose to use GaN quantum dots as building blocks of a solid state quantum bit. The existence of a strong built in electric field induced by the spontaneous polarization and by the piezoelectricity is exploited to entangle the states in coupled quantum dots without external fields. The electro-optical response of the coupled GaN quantum dots is investigated theoretically by means of a realistic description of Coulomb-correlated few-electron states, obtained via a direct-diagonalization approach. We show that the built-in electric field in nitrides induces intrinsic dipole–dipole coupling of the order of some milli-electron-volt and thus allows the implementation of quantum information processing. As an example we will implement the quantum XOR gate. Quantum operations are achieved by a sequence of femtosecond multicolor laser pulses.

Optical quantum gates with semiconductor nanostructures

An all optical implementation of quantum information processing with semiconductor macroatoms is presented. Our quantum hardware consists of an array of semiconductor quantum dots and the computational degrees of freedom, i.e. the qubits, are energy-selected interband optical transitions. The proposed quantum-computing scheme exploits exciton–exciton interactions driven by ultrafast sequences of multi-colour laser pulses. Contrary to existing proposals based on charge excitations, the present all-optical implementation does not require the application of time-dependent electric fields, thus allowing for a sub-picosecond, i.e. decoherence-free, operation time-scale in realistic state-of-the-art semiconductor nanostructures. Moreover, the fully-optical character of the proposed gating scheme makes it an ideal candidate for the realization of all-optical computing networks. Copyright © 2001 John Wiley & Sons, Ltd.

Quantum information processing with semiconductor macroatoms.

An all optical implementation of quantum information processing with semiconductor macroatoms is proposed. Our quantum hardware consists of an array of quantum dots and the computational degrees of freedom are energy-selected interband optical transitions. The quantum-computing strategy exploits exciton-exciton interactions driven by ultrafast multicolor laser pulses. Contrary to existing proposals based on charge excitations, our approach does not require time-dependent electric fields, thus allowing for a subpicosecond, decoherence-free, operation time scale in realistic semiconductor nanostructures.

Advanced Laser Sources for Multiphoton Microscope.

The advanced laser techniques for multiphoton microscope are introduced in terms of femtosecond pulse generation. The compact ultrafast fiber lasers are described as the second generation of femtosecond lasers for microscopy. For the third generation techniques, the advanced techniques such as light propagation control by index profiles in core and clad area are promising. The photonic fiber structure generates the super continuum in 1-m long fiber. Several ideas for multi-color and tunable pulse generation are discussed. The engineering developed for scientific and industrial applications should be combined for the compact and reliable light source for multiphoton microscopy.