13 research outputs found
Measurement of the Optical Conductivity of Graphene
Optical reflectivity and transmission measurements over photon energies
between 0.2 and 1.2 eV were performed on single-crystal graphene samples on a
transparent SiO2 substrate. For photon energies above 0.5 eV, graphene yielded
a spectrally flat optical absorbance of (2.3 +/- 0.2)%. This result is in
agreement with a constant absorbance of pi*alpha, or a sheet conductivity of
pi*e^2/2h, predicted within a model of non-interacting massless Dirac Fermions.
This simple result breaks down at lower photon energies, where both spectral
and sample-to-sample variations were observed. This "non-universal" behavior is
explained by including the effects of doping and finite temperature, as well as
contributions from intraband transitions.Comment: 9 pages, 4 figures, Phys. Rev. Lett. 101, 196405 (2008
Architectures for Multinode Superconducting Quantum Computers
Many proposals to scale quantum technology rely on modular or distributed
designs where individual quantum processors, called nodes, are linked together
to form one large multinode quantum computer (MNQC). One scalable method to
construct an MNQC is using superconducting quantum systems with optical
interconnects. However, a limiting factor of these machines will be internode
gates, which may be two to three orders of magnitude noisier and slower than
local operations. Surmounting the limitations of internode gates will require a
range of techniques, including improvements in entanglement generation, the use
of entanglement distillation, and optimized software and compilers, and it
remains unclear how improvements to these components interact to affect overall
system performance, what performance from each is required, or even how to
quantify the performance of each. In this paper, we employ a `co-design'
inspired approach to quantify overall MNQC performance in terms of hardware
models of internode links, entanglement distillation, and local architecture.
In the case of superconducting MNQCs with microwave-to-optical links, we
uncover a tradeoff between entanglement generation and distillation that
threatens to degrade performance. We show how to navigate this tradeoff, lay
out how compilers should optimize between local and internode gates, and
discuss when noisy quantum links have an advantage over purely classical links.
Using these results, we introduce a roadmap for the realization of early MNQCs
which illustrates potential improvements to the hardware and software of MNQCs
and outlines criteria for evaluating the landscape, from progress in
entanglement generation and quantum memory to dedicated algorithms such as
distributed quantum phase estimation. While we focus on superconducting devices
with optical interconnects, our approach is general across MNQC
implementations.Comment: 23 pages, white pape
Scattering of vibrationally and electronically excited co molecules from a lif(100) surface
Contains fulltext :
98995.pdf (publisher's version ) (Open Access
Nanoscience Research for Energy Needs
This 2004 report details the Department of Energy workshop on the relationship between nanoscale science and technology and the nation's energy needs