79 research outputs found
Optimal Control for Generating Quantum Gates in Open Dissipative Systems
Optimal control methods for implementing quantum modules with least amount of
relaxative loss are devised to give best approximations to unitary gates under
relaxation. The potential gain by optimal control using relaxation parameters
against time-optimal control is explored and exemplified in numerical and in
algebraic terms: it is the method of choice to govern quantum systems within
subspaces of weak relaxation whenever the drift Hamiltonian would otherwise
drive the system through fast decaying modes. In a standard model system
generalising decoherence-free subspaces to more realistic scenarios,
openGRAPE-derived controls realise a CNOT with fidelities beyond 95% instead of
at most 15% for a standard Trotter expansion. As additional benefit it requires
control fields orders of magnitude lower than the bang-bang decouplings in the
latter.Comment: largely expanded version, superseedes v1: 10 pages, 5 figure
Implementation of a Toffoli Gate with Superconducting Circuits
The quantum Toffoli gate allows universal reversible classical computation.
It is also an important primitive in many quantum circuits and quantum error
correction schemes. Here we demonstrate the realization of a Toffoli gate with
three superconducting transmon qubits coupled to a microwave resonator. By
exploiting the third energy level of the transmon qubit, the number of
elementary gates needed for the implementation of the Toffoli gate, as well as
the total gate time can be reduced significantly in comparison to theoretical
proposals using two-level systems only. We characterize the performance of the
gate by full process tomography and Monte Carlo process certification. The gate
fidelity is found to be %.Comment: 4 pages, 5figure
Efficient Algorithms for Optimal Control of Quantum Dynamics: The "Krotov'' Method unencumbered
Efficient algorithms for the discovery of optimal control designs for
coherent control of quantum processes are of fundamental importance. One
important class of algorithms are sequential update algorithms generally
attributed to Krotov. Although widely and often successfully used, the
associated theory is often involved and leaves many crucial questions
unanswered, from the monotonicity and convergence of the algorithm to
discretization effects, leading to the introduction of ad-hoc penalty terms and
suboptimal update schemes detrimental to the performance of the algorithm. We
present a general framework for sequential update algorithms including specific
prescriptions for efficient update rules with inexpensive dynamic search length
control, taking into account discretization effects and eliminating the need
for ad-hoc penalty terms. The latter, while necessary to regularize the problem
in the limit of infinite time resolution, i.e., the continuum limit, are shown
to be undesirable and unnecessary in the practically relevant case of finite
time resolution. Numerical examples show that the ideas underlying many of
these results extend even beyond what can be rigorously proved.Comment: 19 pages, many figure
ADAM17/EGFR axis promotes transglutaminase-dependent skin barrier formation through phosholipase C gamma 1 and protein kinase C pathways
This work was supported by the German Research Foundation DFG (SFB 850/B6) and by the Fritz-Thyssen
foundation (Az.10.14.2.150) to C.-W.F and the Medical Research Council (MR/L010402/1) to D.P.K
Chemical vapour deposition synthetic diamond: materials, technology and applications
Substantial developments have been achieved in the synthesis of chemical
vapour deposition (CVD) diamond in recent years, providing engineers and
designers with access to a large range of new diamond materials. CVD diamond
has a number of outstanding material properties that can enable exceptional
performance in applications as diverse as medical diagnostics, water treatment,
radiation detection, high power electronics, consumer audio, magnetometry and
novel lasers. Often the material is synthesized in planar form, however
non-planar geometries are also possible and enable a number of key
applications. This article reviews the material properties and characteristics
of single crystal and polycrystalline CVD diamond, and how these can be
utilized, focusing particularly on optics, electronics and electrochemistry. It
also summarizes how CVD diamond can be tailored for specific applications,
based on the ability to synthesize a consistent and engineered high performance
product.Comment: 51 pages, 16 figure
The Joint TerraSAR-X / TanDEM-X Mission Planning System
This paper recalls the essential system requirements and
elements for the joint TerraSAR-X / TanDEM-X mission
planning system. Its commissioning approach, tests and
results are described in detail
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