1,782 research outputs found
Recipes for spin-based quantum computing
Technological growth in the electronics industry has historically been
measured by the number of transistors that can be crammed onto a single
microchip. Unfortunately, all good things must come to an end; spectacular
growth in the number of transistors on a chip requires spectacular reduction of
the transistor size. For electrons in semiconductors, the laws of quantum
mechanics take over at the nanometre scale, and the conventional wisdom for
progress (transistor cramming) must be abandoned. This realization has
stimulated extensive research on ways to exploit the spin (in addition to the
orbital) degree of freedom of the electron, giving birth to the field of
spintronics. Perhaps the most ambitious goal of spintronics is to realize
complete control over the quantum mechanical nature of the relevant spins. This
prospect has motivated a race to design and build a spintronic device capable
of complete control over its quantum mechanical state, and ultimately,
performing computations: a quantum computer.
In this tutorial we summarize past and very recent developments which point
the way to spin-based quantum computing in the solid-state. After introducing a
set of basic requirements for any quantum computer proposal, we offer a brief
summary of some of the many theoretical proposals for solid-state quantum
computers. We then focus on the Loss-DiVincenzo proposal for quantum computing
with the spins of electrons confined to quantum dots. There are many obstacles
to building such a quantum device. We address these, and survey recent
theoretical, and then experimental progress in the field. To conclude the
tutorial, we list some as-yet unrealized experiments, which would be crucial
for the development of a quantum-dot quantum computer.Comment: 45 pages, 12 figures (low-res in preprint, high-res in journal)
tutorial review for Nanotechnology; v2: references added and updated, final
version to appear in journa
Quantum Memories. A Review based on the European Integrated Project "Qubit Applications (QAP)"
We perform a review of various approaches to the implementation of quantum
memories, with an emphasis on activities within the quantum memory sub-project
of the EU Integrated Project "Qubit Applications". We begin with a brief
overview over different applications for quantum memories and different types
of quantum memories. We discuss the most important criteria for assessing
quantum memory performance and the most important physical requirements. Then
we review the different approaches represented in "Qubit Applications" in some
detail. They include solid-state atomic ensembles, NV centers, quantum dots,
single atoms, atomic gases and optical phonons in diamond. We compare the
different approaches using the discussed criteria.Comment: 22 pages, 12 figure
Quantum Mechanics of 'Conscious Energy'
This paper is aiming to investigate the physical substrate of conscious process. It will attempt to find out: How does conscious process establish relations between their external stimuli and internal stimuli in order to create reality? How does consciousness devoid of new sensory input result to its
new quantum effects? And how does conscious process gain mass in brain? This paper will also try to locate the origins of consciousness at the level of neurons along with the quantum effects of conscious process
Quantum-dot based photonic quantum networks
Quantum dots embedded in photonic nanostructures have in recent years proven
to be a very powerful solid-state platform for quantum optics experiments. The
combination of near-unity radiative coupling of a single quantum dot to a
photonic mode and the ability to eliminate decoherence processes imply that an
unprecedented light-matter interface can be obtained. As a result,
high-cooperativity photon-emitter quantum interfaces can be constructed opening
a path-way to deterministic photonic quantum gates for quantum-information
processing applications. In the present manuscript, I review current
state-of-the-art on quantum dot devices and their applications for quantum
technology. The overarching long-term goal of the research field is to
construct photonic quantum networks where remote entanglement can be
distributed over long distances by photons
Tunneling-induced restoration of classical degeneracy in quantum kagome ice
Quantum effect is expected to dictate the behavior of physical systems at low temperature. For quantum magnets with geometrical frustration, quantum fluctuation usually lifts the macroscopic classical degeneracy, and exotic quantum states emerge. However, how different types of quantum processes entangle wave functions in a constrained Hilbert space is not well understood. Here, we study the topological entanglement entropy and the thermal entropy of a quantum ice model on a geometrically frustrated kagome lattice. We find that the system does not show a Z(2) topological order down to extremely low temperature, yet continues to behave like a classical kagome ice with finite residual entropy. Our theoretical analysis indicates an intricate competition of off-diagonal and diagonal quantum processes leading to the quasidegeneracy of states and effectively, the classical degeneracy is restored
Point Defects and Localized Excitons in 2D WSe2
Identifying the point defects in 2D materials is important for many
applications. Recent studies have proposed that W vacancies are the predominant
point defect in 2D WSe2, in contrast to theoretical studies, which predict that
chalcogen vacancies are the most likely intrinsic point defects in transition
metal dichalcogenide semiconductors. We show using first principles
calculations, scanning tunneling microscopy (STM) and scanning transmission
electron microscopy experiments, that W vacancies are not present in our
CVD-grown 2D WSe2. We predict that O-passivated Se vacancies (O_Se) and O
interstitials (Oins) are present in 2D WSe2, because of facile O2 dissociation
at Se vacancies, or due to the presence of WO3 precursors in CVD growth. These
defects give STM images in good agreement with experiment. The optical
properties of point defects in 2D WSe2 are important because single photon
emission (SPE) from 2D WSe2 has been observed experimentally. While strain
gradients funnel the exciton in real space, point defects are necessary for the
localization of the exciton at length scales that enable photons to be emitted
one at a time. Using state-of-the-art GW-Bethe-Salpeter-equation calculations,
we predict that only Oins defects give localized excitons within the energy
range of SPE in previous experiments, making them a likely source of previously
observed SPE. No other point defects (O_Se, Se vacancies, W vacancies and Se_W
antisites) give localized excitons in the same energy range. Our predictions
suggest ways to realize SPE in related 2D materials and point experimentalists
toward other energy ranges for SPE in 2D WSe2
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