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IEEE Conference on Electrical Performance of Electronic Packaging and Systems (EPEPS)

Quantum Method of Moments for Characterization of Interconnects

Christopher D. Phillips, Vladimir Okhmatovski

Published Oct 17, 2021• 1 citation
Publisher

Abstract

Here we present two quantum algorithms: The Harrow/Hassidim/Lloyd (HHL) algorithm, and a Hamiltonian simulation procedure. Together, these algorithms provide a framework for the solution of general matrix equations using quantum computers. We also demonstrate the practical applicability of this method by means of a charge extraction problem using a quantum method of moments.

DOI
10.1109/epeps51341.2021.9609209

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Here we present two quantum algorithms: The Harrow/Hassidim/Lloyd (HHL) algorithm, and a Hamiltonian simulation procedure. Together, these algorithms provide a framework for the solution of general matrix equations using quantum computers. We also demonstrate the practical applicability of this method by means of a charge extraction problem using a quantum method of moments.
Quantum computation offers a promising alternative to classical computing methods in many areas of numerical science, with algorithms that make use of the unique ways in which quantum computers store and manipulate data often achieving dramatic improvements in performance over their classical counterparts. The potential efficiency of quantum computers is particularly important for numerical simulations, where the capabilities of classical computing systems are often insufficient for the analysis of real-world problems. In this work, we study problems involving the solution of matrix equations, for which there is limited research on efficient, general, and fully implemented quantum procedures. We develop a generalization of the Harrow/Hassidim/Lloyd algorithm by providing an alternative unitary for eigenphase estimation. This unitary, which we have adopted from research in the area of quantum walks, has the advantage of being well defined for any arbitrary matrix equation, thereby allowing the solution procedure to be directly implemented on quantum hardware for any well-conditioned system. The procedure is most useful for sparse matrix equations, as it allows for the inverse of a matrix to be applied with O(sN log(N)) complexity, where N is the number of unknowns, and s is an upper bound on the number of nonzero elements in any row of the system matrix. This efficiency is competitive with the most sophisticated available classical solvers, and is independent of the structure of the input matrix. Hence, this procedure represents an important step towards the achievement of quantum advantage over classical algorithms for practical problems in numerical science.
Quantum simulation of electromagnetic (EM) structures is still in its infancy. In this paper, we investigate the possibility of applying quantum computing to solve the finite element equations for EM problems. Specifically, we propose to leverage a milestone in quantum computing, i.e., the Harrow/Hassidim/Lloyd (HHL) algorithm, to solve the finite element equations in the EM domain. To do this, we first present a systematic method to reformulate the finite element equations into quantum computation format and apply the HHL algorithm to solve the new equations. Taking advantage of the special properties of finite element matrices in EM problems, we then devise a stepwise algorithm to efficiently determine the suitable values for the hyperparameters of HHL. The proposed method can in theory solve the EM finite element equations in logarithmic time relative to the size of the finite element matrix. This is exponentially faster than that achievable by classical computation as the matrix size increases. A two-dimensional EM example is used to illustrate how the proposed method can be used to find the solutions to EM problems through quantum computation.
In this work, we investigate the Harrow-Hassidim-Lloyd (HHL) quantum algorithm for the solution of electric field integral equation (EFIE)-based matrix equation system for analyzing electromagnetic scattering from three-dimensional (3D) perfect electrically conducting (PEC) objects. The HHL algorithm is one of the representative quantum algorithms for the solution of linear equation systems. Numerical experiments are presented to investigate the computational cost and accuracy of the HHL algorithm for solving the EFIE matrix equation system executed on the virtual simulator on the classical computers.
The Harrow-Hassidim-Lloyd (HHL) quantum algorithm for sampling from the solution of a linear system provides an exponential speed-up over its classical counterpart. The problem of solving a system of linear equations has a wide scope of applications, and thus HHL constitutes an important algorithmic primitive. In these notes, we present the HHL algorithm and its improved versions in detail, including explanations of the constituent sub- routines. More specifically, we discuss various quantum subroutines such as quantum phase estimation and amplitude amplification, as well as the important question of loading data into a quantum computer, via quantum RAM. The improvements to the original algorithm exploit variable-time amplitude amplification as well as a method for implementing linear combinations of unitary operations (LCUs) based on a decomposition of the operators using Fourier and Chebyshev series. Finally, we discuss a linear solver based on the quantum singular value estimation (QSVE) subroutine.
Solving linear systems of equations plays a fundamental role in numerous computational problems from different fields of science. The widespread use of numerical methods to solve these systems motivates investigating the feasibility of solving linear systems problems using quantum computers. In this work, we provide a survey of the main advances in quantum linear systems algorithms, together with some applications. We summarize and analyze the main ideas behind some of the algorithms for the quantum linear systems problem in the literature. The analysis begins by examining the Harrow-Hassidim-Lloyd (HHL) solver. We note its limitations and reliance on computationally expensive quantum methods, then highlight subsequent research efforts which aimed to address these limitations and optimize runtime efficiency and precision via various paradigms. We focus in particular on the post-HHL enhancements which have paved the way towards optimal lower bounds with respect to error tolerance and condition number. By doing so, we propose a taxonomy that categorizes these studies. Furthermore, by contextualizing these developments within the broader landscape of quantum computing, we explore the foundational work that have inspired and informed their development, as well as subsequent refinements. Finally, we discuss the potential applications of these algorithms in differential equations, quantum machine learning, and many-body physics.