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 semiconductor quantum dots and the computational degrees of freedom are energy-selected interband optical transitions. The proposed quantum-computing strategy exploits exciton-exciton interactions driven by ultrafast sequences of multi-color 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.Comment: 11 pages, 5 figures, to be published in Phys. Rev. Lett., significant changes in the text and new simulations (figure 3

Tailoring exciton-exciton Coulomb coupling in semiconductor macroatoms using an external electric field

We present a novel approach for the control of exciton-exciton Coulomb coupling in semiconductor macroatoms/molecules. We exploit electron-hole charge separations induced by the presence of a static external electric field: in this way excitonic dipoles are significantly reinforced. This, in turn, allows us to control and magnify intra- as well as interdot few-exciton effects connected to dipole-dipole coupling. This mechanism will be accounted for within a simple analytical model, which is found to be in good agreement with fully three-dimensional calculations. The proposed approach allows to control and tune exciton-exciton Coulomb coupling, a key quantity for the design and realization of novel single-electron/exciton devices

GaN quantum dot based quantum information/computation processing

Abstract 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

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 multicolour laser pulses. Contrary to existing proposals based on charge excitations, the present all-optical implementation does not require the application of time-dependent electric !elds, 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

Ultrafast Quantum Information Processing in Nanostructured Semiconductors

We shall review two implementation proposals for quantum information processing based on charge degrees of freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees of freedom in this proposal are interband optical transitions driven by ultrafast sequences of multicolor laser-pulse trains. The conditional dynamics necessary for universal quantum computation is provided by exciton-exciton coupling between different quantum dots in an array. We shall also discuss an alternative scheme based on transport of ballistic electrons in coupled semiconductor quantum wires. In the framework of such implementation strategy, we shall finally discuss a potential simple way for testing violation of Bell's inequality in a condensed-matter setting

All optical spin-based quantum information processing

We propose a spin-based ultra-fast laser driven implementation of quantum information processing based on the Pauli blocking effect in semiconductors, which acts as a spin dependent switching mechanism for auxiliary exciton states

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

Quantum information processing using semiconductor nanostructures

We shall review two implementation proposals for quantum information processing based on charge degrees-of-freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees-of-freedom in this proposal are interband optical transitions driven by ultrafast sequences of multicolor laser-pulse trains. The conditional dynamics necessary for universal quantum computation is provided by exciton-exciton coupling between different quantum dots in an array. We shall also discuss an alternative scheme based on transport of ballistic electrons in coupled semiconductor quantum wires. In the framework of such implementation strategy, we shall finally discuss a potential simple way for testing violation of Bell's inequality in a condensed-matter setting

Electro-optical properties of semiconductor quauntums 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 intradot and interdot—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