17,618 research outputs found
Chirality distribution and transition energies of carbon nanotubes
From resonant Raman scattering on isolated nanotubes we obtained the optical
transition energies, the radial breathing mode frequency and Raman intensity of
both metallic and semiconducting tubes. We unambiguously assigned the chiral
index (n_1,n_2) of approximately 50 nanotubes based solely on a third-neighbor
tight-binding Kataura plot and find omega_RBM=214.4cm^-1nm/d+18.7cm^-1. In
contrast to luminescence experiments we observe all chiralities including
zig-zag tubes. The Raman intensities have a systematic chiral-angle dependence
confirming recent ab-initio calculations.Comment: 4 pages, to be published in Phys. Rev. Let
Exploiting Non-Markovianity of the Environment for Quantum Control
When the environment of an open quantum system is non-Markovian, amplitude
and phase flow not only from the system into the environment but also back.
Here we show that this feature can be exploited to carry out quantum control
tasks that could not be realized if the system was isolated. Inspired by recent
experiments on superconducting phase circuits, we consider an anharmonic ladder
with resonant amplitude control only. This restricts realizable operations to
SO(N). The ladder is immersed in an environment of two-level systems. Strongly
coupled two-level systems lead to non-Markovian effects, whereas the weakly
coupled ones result in single-exponential decay. Presence of the environment
allows for implementing diagonal unitaries that, together with SO(N), yield the
full group SU(N). Using optimal control theory, we obtain errors that are
solely -limited
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