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AIP conference proceedings

Nondirect product discrete variable representation in multidimensional quantum problems

Vladimir S. Melezhik

Published Jan 1, 2012• 4 citations
Publisher

Abstract

We have developed a method for treating different quantum few-body dynamics without traditional partial-wave analysis. The key element of the method is a nondirect product discrete variable representation (npDVR) we have suggested and developed in application to the time-dependent mutidimensional Schrödinger equations. It happened that this approach was very efficient in quantitative analysis of low-dimensional ultracold few-body systems arising in confined geometry of atomic traps. As an example, we consider the numerical analysis of the four-dimensional Schrödinger equation describing the resonant molecule formation in confined two-component atomic mixture with transferring the energy release to the center-ofmass excitation of forming molecules.

DOI
10.1063/1.4756366

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We have developed a method for treating different quantum few-body dynamics without traditional partial-wave analysis. The key element of the method is a nondirect product discrete variable representation (npDVR) we have suggested and developed in application to the time-dependent mutidimensional Schrödinger equations. It happened that this approach was very efficient in quantitative analysis of low-dimensional ultracold few-body systems arising in confined geometry of atomic traps. As an example, we consider the numerical analysis of the four-dimensional Schrödinger equation describing the resonant molecule formation in confined two-component atomic mixture with transferring the energy release to the center-ofmass excitation of forming molecules.
We discuss computational aspects of the developed mathematical models for ultracold few-body processes in atomic traps. The key element of the elaborated computational schemes is a nondirect product discrete variable representation (npDVR) we have suggested and applied to the time-dependent and stationary Schrödinger equations with a few spatial variables. It turned out that this approach is very effcient in quantitative analysis of low-dimensional ultracold few-body systems arising in confined geometry of atomic traps. The effciency of the method is demonstrated here on two examples. A brief review is also given of novel results obtained recently.
We have developed an efficient computational method for solving the quantum multichannel scattering problem with a nonseparable angular part. The use of the nondirect product discrete-variable representation, suggested and developed by V. Melezhik, gives us an accurate approximation for the angular part of the desired wave function and, eventually, for the scattering parameters. Subsequent reduction of the problem to the boundary-value problem with well-defined block-band matrix of equation coefficients permits us to use efficient standard algorithms for its solution. We demonstrate the numerical efficiency, flexibility, and good convergence of the computational scheme in a quantitative description of the Feshbach resonances in pair collisions occurring in atomic traps and the scattering in strongly anisotropic traps. The method can also be used for the investigation of further actual problems in quantum physics. A natural extension is a description of spin-orbit coupling, intensively investigated in ultracold gases, and dipolar confinement-induced resonances.
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We have suggested a method for treating different quantum few-body dynamics without traditional using of the partial-wave analysis. It happened that this approach was very efficient in quantitative analysis of low-dimensional ultracold few-body systems arising in confined geometry of atomic traps. Here we discuss its application to a recently suggested mechanism of resonant molecule formation in confined two-component atomic mixture with transferring the energy release to the center-of-mass excitation of forming molecules. The author considers this result as one of the most significant in his scientific carrier which started from the model of resonant muonic molecule formation [S.I. Vinitsky et al., Sov. Phys. JETP 47 , 444 (1978)], one of the most citing works of S.I. Vinitsky.
We develop a computationally and numerically efficient method to calculate binding energies and corresponding wave functions of quantum mechanical three-body problems in low dimensions. Our approach exploits the tensor structure of the multidimensional stationary Schrödinger equation, being expressed as a discretized linear eigenvalue problem. In one spatial dimension, we solve the three-body problem with the help of iterative methods. Here the application of the Hamiltonian operator is represented by dense matrix–matrix products. In combination with a newly-designed preconditioner for the Jacobi–Davidson QR, our highly accurate tensor method offers a significantly faster computation of three-body energies and bound states than other existing approaches. For the two-dimensional case, we additionally make use of a hybrid distributed/shared memory parallel implementation to calculate the corresponding three-body energies. Our novel method is of high relevance for the analysis of few-body systems and their universal behavior, which is only governed by the particle masses, overall symmetries, and the spatial dimensionality. Our results have straightforward applications for ultracold atomic gases that are widespread and nowadays utilized in quantum sensors.
The finite-element discrete variable representation is proposed to express the nonequilibrium Green's function for strongly inhomogeneous quantum systems. This method is highly favorable against a general basis approach with regard to numerical complexity, memory resources, and computation time. Its flexibility also allows for an accurate representation of spatially extended Hamiltonians and thus opens the way toward a direct solution of the two-time Schwinger-Keldysh-Kadanoff-Baym equations on spatial grids, including, for example, the description of highly excited states in atoms. As benchmarks, we compute and characterize, in Hartree-Fock and second Born approximations, the ground states of the He atom, the H2{\mathrm{H}}_{2}H2​ molecule, and the LiH molecule in one spatial dimension. Thereby, the ground-state and binding energies, densities, and bond lengths are compared with the direct solution of the time-dependent Schr\"odinger equation.