4,270 research outputs found
Adaptive propagation of quantum few-body systems with time-dependent Hamiltonians
In this study, a variety of methods are tested and compared for the numerical
solution of the Schr\"odinger equation for few-body systems with explicitely
time-dependent Hamiltonians, with the aim to find the optimal one. The
configuration interaction method, generally applied to find stationary
eigenstates accurately and without approximations to the wavefunction's
structure, may also be used for the time-evolution, which results in a large
linear system of ordinary differential equations. The large basis sizes
typically present when the configuration interaction method is used calls for
efficient methods for the time evolution. Apart from efficiency, adaptivity (in
the time domain) is the other main focus in this study, such that the time step
is adjusted automatically given some requested accuracy. A method is suggested
here, based on an exponential integrator approach, combined with different ways
to implement the adaptivity, which was found to be faster than a broad variety
of other methods that were also considered.Comment: 16 pages, 1 figure (4 panels
Implicit ODE solvers with good local error control for the transient analysis of Markov models
Obtaining the transient probability distribution vector of a continuous-time Markov chain (CTMC) using an implicit ordinary differential equation (ODE) solver tends to be advantageous in terms of run-time computational cost when the product of the maximum output rate of the CTMC and the largest time of interest is large. In this paper, we show that when applied to the transient analysis of CTMCs, many implicit ODE solvers are such that the linear systems involved in their steps can be solved by using iterative methods with strict control of the 1-norm of the error. This allows the development of implementations of those ODE solvers for the transient analysis of CTMCs that can be more efficient and more accurate than more standard implementations.Peer ReviewedPostprint (published version
Colloquium: Trapped ions as quantum bits -- essential numerical tools
Trapped, laser-cooled atoms and ions are quantum systems which can be
experimentally controlled with an as yet unmatched degree of precision. Due to
the control of the motion and the internal degrees of freedom, these quantum
systems can be adequately described by a well known Hamiltonian. In this
colloquium, we present powerful numerical tools for the optimization of the
external control of the motional and internal states of trapped neutral atoms,
explicitly applied to the case of trapped laser-cooled ions in a segmented
ion-trap. We then delve into solving inverse problems, when optimizing trapping
potentials for ions. Our presentation is complemented by a quantum mechanical
treatment of the wavepacket dynamics of a trapped ion. Efficient numerical
solvers for both time-independent and time-dependent problems are provided.
Shaping the motional wavefunctions and optimizing a quantum gate is realized by
the application of quantum optimal control techniques. The numerical methods
presented can also be used to gain an intuitive understanding of quantum
experiments with trapped ions by performing virtual simulated experiments on a
personal computer. Code and executables are supplied as supplementary online
material (http://kilian-singer.de/ent).Comment: accepted for publication in Review of Modern Physics 201
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