The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.
"These photons can be used for linear optics quantum computation , quantum communication , and quantum sensing . Furthermore, the electron or hole spins in charged quantum dots could be used as local memories  , which is a prerequisite to build quantum networks . Indistinguishable single photons on demand are essential in order to realize these technologies. "
[Show abstract][Hide abstract] ABSTRACT: In this letter, we present a detailed, all optical study of the influence of
different excitation schemes on the indistinguishability of single photons from
a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel
interference of consecutive photons from the spontaneous emission of an InAs
quantum dot state under various excitation schemes and different excitation
conditions and give a comparison.
"Luminescence properties: QDs are semiconductor 11. nanocrystals that possess unique optical properties including broad-range excitation, size-tunable narrow emission spectra, and high photo stability, giving them considerable value in various applications (Kroutvar et al. 2004). The size and composition of QDs can be varied to obtain the desired emission properties and make them amenable to simultaneous detection of multiple targets. "
[Show abstract][Hide abstract] ABSTRACT: Quantum dots (QDs) have captured the fascination and attention of scientists due to their simultaneous targeting and imaging potential in drug delivery, in pharmaceutical and biomedical applications. In the present study, we have exhaustively reviewed various aspects of QDs, highlighting their pharmaceutical and biomedical applications, pharmacology, interactions, and toxicological manifestations. The eventual use of QDs is to dramatically improve clinical diagnostic tests for early detection of cancer. In recent years, QDs were introduced to cell biology as an alternative fluorescent probe.
"The superposition of one and zero states is the power of quantum computers, and it differs from classical computers. Spins of electron and holes in quantum dots are good candidates for the logical units in quantum computers (Loss and Divincenzo1998, Petta et al. 2005, Kroutvar et al. 2004). Nanostructures such as quantum dots can confine a single electron or hole in nanometer space. "
[Show abstract][Hide abstract] ABSTRACT: In recent years, spins of confined carriers in quantum dots are promising candidates for the logical units in quantum computers. In many concepts developed so far, the individual spin q-bits are being manipulated by magnetic fields, which is difficult to achieve. In the current research the recent developments of spin based quantum computing has been reviewed. Then, Single-hole spin in a molecular quantum dots with less energy and more speed has been electrically manipulated and the results have been compared with the magnetic manipulating of the spin.
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