Time-optimal Hamiltonian simulation and gate synthesis using homogeneous local unitaries

Motivated by experimental limitations commonly met in the design of solid state quantum computers, we study the problems of non-local Hamiltonian simulation and non-local gate synthesis when only homogeneous local unitaries are performed in order to tailor the available interaction. Homogeneous (i.e. identical for all subsystems) local manipulation implies a more refined classification of interaction Hamiltonians than the inhomogeneous case, as well as the loss of universality in Hamiltonian simulation. For the case of symmetric two-qubit interactions, we provide time-optimal protocols for both Hamiltonian simulation and gate synthesis.Comment: 7 page

Privacy e riconoscimento di figlio naturale: spunti comparatistici.

L'allargamento del raggio di incidenza del diritto alla riservatezza in campi e settori inesplorati o finora ignorati del diritto di famiglia e la conseguente necessit\ue0 del suo coordinamento con altri valori e princ\uecpi ordinamentali (quali quelli relativi allo svolgimento di un equo processo) confermano come tale diritto sia entrato a far parte in modo strutturale del patrimonio culturale del diritto civile e come la relativa tutela debba costituire un punto fermo sia in campo legislativo che giurisprudenziale.\uc8 utile, a questo punto della ricerca, porre a raffronto le posizioni assunte dal diritto italiano e da quello inglese a proposito del tema che si \ue8 finora affrontato. In particolare, l'ordinamento italiano appare ancora carente di disposizioni legislative espressamente e specificamente ispirate alla tutela della riservatezza del minore, nell'ambito della procedura per il riconoscimento dei figli naturali, in un'ottica di salvaguardia del suo effettivo benessere materiale e psichico, e necessita di interventi legislativi mirati

High coherent solid-state qubit from a pair of quantum dots

In this letter we propose a scheme to build up high coherent solid-state quantum bit (qubit) from two coupled quantum dots. Quantum information is stored in electron-hole pair state with the electron and hole locating in different dots, and universal quantum gates involving any pair of qubits are realized by effective coupling interaction via virtually exchanging cavity photons.Comment: 3 pages, 1 figur

Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits

A quantum dot spin LED provides a test of carrier spin injection into a qubit, as well as a means of analyzing carrier spin injection in general and local spin polarization. The polarization of the observed light is, however, significantly influenced by the dot geometry so the spin may be more polarized than the emitted light would naively suggest. We have calculated carrier polarization-dependent optical matrix elements using 8-band strain-dependent k.p theory for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. The observed circular polarization does not depend on whether the injected spin-polarized carriers are electrons or holes, but is strongly influenced by the SAQD geometry and emission direction. Calculations for typical SAQD geometries with emission along [110] show light that is only ~5% circularly polarized for spin states that are 100% polarized along [110]. Therefore observed polarizations [Chye et al. PRB 66, 201301(R)] of ~1% imply a spin polarization within the dot of ~20%. We also find that measuring along the growth direction gives near unity conversion of spin to photon polarization, and is the least sensitive to uncertainties in SAQD geometry.Comment: 4 pages, 6 figure

Optical Manipulation of Single Electron Spin in Doped and Undoped Quantum Dots

The optical manipulation of electron spins is of great benefit to solid-state quantum information processing. In this letter, we provide a comparative study on the ultrafast optical manipulation of single electron spin in the doped and undoped quantum dots. The study indicates that the experimental breakthrough can be preliminarily made in the undoped quantum dots, because of the relatively less demand.Comment: 3 pages, 3 figure