1,952 research outputs found
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
Complete controllability of quantum systems
Sufficient conditions for complete controllability of -level quantum
systems subject to a single control pulse that addresses multiple allowed
transitions concurrently are established. The results are applied in particular
to Morse and harmonic-oscillator systems, as well as some systems with
degenerate energy levels. Morse and harmonic oscillators serve as models for
molecular bonds, and the standard control approach of using a sequence of
frequency-selective pulses to address a single transition at a time is either
not applicable or only of limited utility for such systems.Comment: 8 pages, expanded and revised versio
Optimal Control of One-Qubit Gates
We consider the problem of carrying an initial Bloch vector to a final Bloch
vector in a specified amount of time under the action of three control fields
(a vector control field). We show that this control problem is solvable and
therefore it is possible to optimize the control. We choose the physically
motivated criteria of minimum energy spent in the control, minimum magnitude of
the rate of change of the control and a combination of both. We find exact
analytical solutions.Comment: 5 page
An optical linewidth study of a chromoprotein-C-phycocyanin in a low-temperature glass
The temperature dependence of spectral holes burnt into a phycocyanin-doped ethylene glycol/water glass is investigated in the temperature range between 1.5 and 15 K. The data are well described by a power law with an exponent of 1.16 ± 0.1. Chromoproteins thus behave very much the same as glasses doped with small impurity molecules
First Order Static Excitation Potential: Scheme for Excitation Energies and Transition Moments
We present an approximation scheme for the calculation of the principal
excitation energies and transition moments of finite many-body systems. The
scheme is derived from a first order approximation to the self energy of a
recently proposed extended particle-hole Green's function. A hermitian
eigenvalue problem is encountered of the same size as the well-known Random
Phase Approximation (RPA). We find that it yields a size consistent description
of the excitation properties and removes an inconsistent treatment of the
ground state correlation by the RPA. By presenting a hermitian eigenvalue
problem the new scheme avoids the instabilities of the RPA and should be well
suited for large scale numerical calculations. These and additional properties
of the new approximation scheme are illuminated by a very simple exactly
solvable model.Comment: 15 pages revtex, 1 eps figure included, corrections in Eq. (A1) and
Sec. II
Identifying an Experimental Two-State Hamiltonian to Arbitrary Accuracy
Precision control of a quantum system requires accurate determination of the
effective system Hamiltonian. We develop a method for estimating the
Hamiltonian parameters for some unknown two-state system and providing
uncertainty bounds on these parameters. This method requires only one
measurement basis and the ability to initialise the system in some arbitrary
state which is not an eigenstate of the Hamiltonian in question. The scaling of
the uncertainty is studied for large numbers of measurements and found to be
proportional to one on the square-root of the number of measurements.Comment: Minor corrections, Accepted for publication in Physical Review
Influence of chromophores on quarternary structure of phycobiliproteins from the cyanobacterium, Mastigocladus laminosus
Chromophores of C-phycocyanin and phycoerythrο-cyanin have been chemically modified by reduction to
rubins , bleaching , photoisomerization , or perturbation
with bulky substituents. Pigments containing modified
chromophores, or hybrids containing modified and unmodified chromophores in individual protomers have been prepared. All modifications inhibit the association of the
(aß)-protomers of these pigments to higher aggregates. The
results demonstrate a pronounced effect of the state of
the chromophores on biliprotein quaternary structure. It
may be important in phycobi1isome assembly , and also in
the dual function of biliproteins as (i) antenna pigments
for photosynthesis and (ii) reaction centers for photomor-phogenesis
GaBoDS: The Garching-Bonn Deep Survey - III. Lyman-Break Galaxies in the Chandra Deep Field South
We present first results of our search for high-redshift galaxies in deep CCD
mosaic images. As a pilot study for a larger survey, very deep images of the
Chandra Deep Field South (CDFS), taken withWFI@MPG/ESO2.2m, are used to select
large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break
method. The data of these Lyman-break galaxies are made public as an electronic
table. These objects are good candidates for galaxies at z~3 and z~4 which is
supported by their photometric redshifts. The distributions of apparent
magnitudes and the clustering properties of the two populations are analysed,
and they show good agreement to earlier studies. We see no evolution in the
comoving clustering scale length from z~3 to z~4. The techniques presented here
will be applied to a much larger sample of U-dropouts from the whole survey in
near future.Comment: 11 pages, 11 figures, replaced with version accepted by A&A. Minor
changes and tabular appendix with LBG catalogues. Version with full
resolution figures available at
http://www.astro.uni-bonn.de/~hendrik/2544.pd
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