How Noisy Quantum Computers work part2(Quantum Computing) | by Monodeep Mukherjee | Nov, 2022

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  1. Assessing the stability of noisy quantum computing(arXiv)

Author : Samudra Dasgupta, Travis S. Humble

Summary : Quantum computing has made considerable progress in the last decade with multiple emerging technologies providing proof-of-principle experimental demonstrations of such calculations. However, these experimental demonstrations of quantum computing face technical challenges due to noise and errors that arise from the imperfect implementation of the technology. Here, we frame the concepts of computational precision, reproducibility of results, device reliability, and program stability in the context of quantum computing. We provide intuitive definitions for these concepts in the context of quantum computing that lead to operationally meaningful limits on the program output. Our evaluation highlights the continued need for statistical analysis of the quantum computing program to increase our confidence in the burgeoning field of quantum information science.

two. Calculating the energy of the ground state of benzene under spatial deformations with noisy quantum computing(arXiv)

Author : Wassil Sennane, Jean-Philip Piquemal, Marko J. Rancić

Summary : In this manuscript, we calculate the ground state energy of benzene under spatial deformations using the variational quantum eigensolver (VQE). The main goal of the study is to estimate the feasibility of using ansatze quantum computing in short-term devices to solve problems with a large number of orbitals in regions where classical methods are known to fail. Furthermore, by combining our advanced simulation platform with real quantum computers, we provide an analysis of how noise, inherent in quantum computers, affects the results. The centers of our study are the hardware efficient quantum unitary coupled cluster (qUCC) ansatze. First, we find that efficient ansatz hardware has the potential to outperform mean-field methods for extreme benzene deformations. However, key issues remain in balance, preventing actual chemical application. Furthermore, the efficient hardware ansatz produces results that are highly dependent on the initial assumption of the parameters, both in the noisy and non-noisy cases, and optimization problems have a greater impact on their convergence than noise. This is confirmed by comparison with real quantum computing experiments. On the other hand, the alternative qUCC ansatz exhibits deeper circuits. Therefore, noise effects are magnified and so extreme that the method never exceeds mean field theories. Our qUCC 8–16 qubit QPU computations/dual simulator appears to be much more sensitive to hardware noise than shot noise, giving further indications of where noise reduction efforts should be directed. Finally, the study shows that the qUCC method better captures the physics of the system since the qUCC method can be used together with the Huckel approximation. We discuss how going beyond this approximation considerably increases the optimization complexity of such a difficult problem. △ Less

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3.Efficient performance improvement of noisy quantum computers (arXiv)

Author : Samuele Ferracin, Akel Hashim, Jean-Loup Ville, Ravi Naik, Arnaud Carignan-Dugas, Hammam Qassim, Alexis Morvan, David I. Santiago, Irfan Siddiqi, Joel J. Wallman

Summary : Using quantum computers in the short term to achieve a quantum advantage requires efficient strategies to improve the performance of the noisy quantum devices available today. We developed and experimentally validated two efficient error mitigation protocols called “Noiseless Output Extrapolation” and “Pauli Error Cancellation” that can drastically improve the performance of quantum circuits composed of noisy gate cycles. By combining popular mitigation strategies such as probabilistic error cancellation and noise amplification with efficient noise reconstruction methods, our protocols can mitigate a wide range of noise processes that do not satisfy the assumptions underlying existing mitigation protocols, including non-local and gate-dependent processes. We test our protocols on a four-qubit superconducting processor in the Advanced Quantum Testbed. We see significant performance improvements for structured and random circuits, with up to 86% improvement in variance distance over unmitigated outputs. Our experiments demonstrate the effectiveness of our protocols, as well as their practicality for today’s hardware platforms.

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