30,202 research outputs found
Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond
We investigate spin-dependent decay and intersystem crossing in the optical
cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We
use spin control and pulsed optical excitation to extract both the
spin-resolved lifetimes of the excited states and the degree of
optically-induced spin polarization. By optically exciting the centre with a
series of picosecond pulses, we determine the spin-flip probabilities per
optical cycle, as well as the spin-dependent probability for intersystem
crossing. This information, together with the indepedently measured decay rate
of singlet population provides a full description of spin dynamics in the
optical cycle of NV centres. The temperature dependence of the singlet
population decay rate provides information on the number of singlet states
involved in the optical cycle.Comment: 11 pages, 5 figure
One-Point Probability Distribution Functions of Supersonic Turbulent Flows in Self-Gravitating Media
Turbulence is essential for understanding the structure and dynamics of
molecular clouds and star-forming regions. There is a need for adequate tools
to describe and characterize the properties of turbulent flows. One-point
probability distribution functions (pdf's) of dynamical variables have been
suggested as appropriate statistical measures and applied to several observed
molecular clouds. However, the interpretation of these data requires comparison
with numerical simulations. To address this issue, SPH simulations of driven
and decaying, supersonic, turbulent flows with and without self-gravity are
presented. In addition, random Gaussian velocity fields are analyzed to
estimate the influence of variance effects. To characterize the flow
properties, the pdf's of the density, of the line-of-sight velocity centroids,
and of the line centroid increments are studied. This is supplemented by a
discussion of the dispersion and the kurtosis of the increment pdf's, as well
as the spatial distribution of velocity increments for small spatial lags. From
the comparison between different models of interstellar turbulence, it follows
that the inclusion of self-gravity leads to better agreement with the observed
pdf's in molecular clouds. The increment pdf's for small spatial lags become
exponential for all considered velocities. However, all the processes
considered here lead to non-Gaussian signatures, differences are only gradual,
and the analyzed pdf's are in addition projection dependent. It appears
therefore very difficult to distinguish between different physical processes on
the basis of pdf's only, which limits their applicability for adequately
characterizing interstellar turbulence.Comment: 38 pages (incl. 17 figures), accepted for publication in ApJ, also
available with full resolution figures at
http://www.strw.leidenuniv.nl/~klessen/Preprint
Complex band structure and plasmon lattice Green's function of a periodic metal-nanoparticle chain
When the surface plasmon resonance in a metal-nanoparticle chain is excited
at one point, the response signal will generally decay down the chain due to
absorption and radiation losses. The decay length is a key parameter in such
plasmonic systems. By studying the plasmon lattice Green's function, we found
that the decay length is generally governed by two exponential decay constants
with phase factors corresponding to guided Bloch modes and one power-law decay
with a phase factor corresponding to that of free space photons. The results
show a high level of similarity between the absorptive and radiative decay
channels. By analyzing the poles (and the corresponding residues) of the
Green's function in a transformed complex reciprocal space, the dominant decay
channel of the real-space Green's function is understood.Comment: 19 pages, 3 figure
ENERGY TRANSFER IN TRIMERIC C-PHYCOCYANIN STUDIED BY PICOSECOND FLUORESCENCE KINETICS
The excited state kinetics of trimeric C-phycocyanin from Mastigocladus laminosus has been measured as a function of the emission and excitation wavelength by the single-photon timing technique with picosecond resolution and simultaneous data analysis. A fast decay component of 22 ps (C-phycocyanin with linker peptides) and 36 ps (C-phycocyanin lacking linker peptides) is attributed to efficient energy transfer from sensitizing to fluorescing chromophores. At long detection wavelengths the fast decay components are found to turn into a rise term. This finding further corroborates the concept of intramolecular energy transfer. Previous reports on the conformational heterogeneity of the chromophores and/or proteins in C-phycocyanin are confirmed. Our data also provide indications for the importance of the uncoloured linker peptides for this heterogeneity
Analyzing conformational changes in single FRET-labeled A1 parts of archaeal A1AO-ATP synthase
ATP synthases utilize a proton motive force to synthesize ATP. In reverse,
these membrane-embedded enzymes can also hydrolyze ATP to pump protons over the
membrane. To prevent wasteful ATP hydrolysis, distinct control mechanisms exist
for ATP synthases in bacteria, archaea, chloroplasts and mitochondria.
Single-molecule F\"orster resonance energy transfer (smFRET) demonstrated that
the C-terminus of the rotary subunit epsilon in the Escherichia coli enzyme
changes its conformation to block ATP hydrolysis. Previously we investigated
the related conformational changes of subunit F of the A1AO-ATP synthase from
the archaeon Methanosarcina mazei G\"o1. Here, we analyze the lifetimes of
fluorescence donor and acceptor dyes to distinguish between smFRET signals for
conformational changes and potential artefacts.Comment: 12 pages, 6 figure
Randomized benchmarking with gate-dependent noise
We analyze randomized benchmarking for arbitrary gate-dependent noise and
prove that the exact impact of gate-dependent noise can be described by a
single perturbation term that decays exponentially with the sequence length.
That is, the exact behavior of randomized benchmarking under general
gate-dependent noise converges exponentially to a true exponential decay of
exactly the same form as that predicted by previous analysis for
gate-independent noise. Moreover, we show that the operational meaning of the
decay parameter for gate-dependent noise is essentially unchanged, that is, we
show that it quantifies the average fidelity of the noise between ideal gates.
We numerically demonstrate that our analysis is valid for strongly
gate-dependent noise models. We also show why alternative analyses do not
provide a rigorous justification for the empirical success of randomized
benchmarking with gate-dependent noise.Comment: It measures what you expect. Comments welcome. v2: removed an
inconsistent assumption from theorem 3 and clarified discussion of prior
work. Results unchanged. v3: further clarified discussion of prior work,
numerics now available at https://github.com/jjwallman/numerics. v4: licence
change as required by Quantu
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