A novel way to estimate expectation values on quantum computers — Estimation of expectation values is a key ingredient in variational quantum algorithms [1], regarded as promising candidates for industrial applications of near-term quantum computers. A challenge in the standard ways of expectation value estimation is the necessity to repeat measurement many times to suppress statistical fluctuation, especially in the application…

Methods to calculate an indispensable tool in quantum physics — Introduction For the past few years, we have witnessed the advent of near-term quantum computers, or noisy intermediate-scale quantum (NISQ) devices [1]. NISQ devices consist of several tens or hundreds of qubits that are not equipped with error correction and are prone to noise. Owing to these reasons, NISQ devices…

Learning wavefunctions of molecules in quantum chemistry — Introduction: the advent of quantum computers and machine learning For some problems in physical science, we need to take care of quantum information to compute or simulate target physics because it is described by quantum mechanics. In most cases, however, it is hard to handle such quantum information on…

While classical computers have bits representing either 0 or 1 values, quantum computers have qubits which provide arbitrary superposition of the bases |0〉and |1〉of quantum states. This intrinsic difference forms the powerfulness of quantum computers overwhelming classical computers. Though the quantum computer’s full potential is still in progress, we are…

“Symmetry” appears everywhere in modern physics, and it plays a significant role in understanding various properties of a quantum system. When a quantum system has symmetry, the energy spectrum/states of the system can be classified according to the symmetry; it is known that the symmetry introduces a conserved quantity C…

Calculating transition amplitudes of Azobenzene isomers using Honeywell System Model HØ — In June 2020, Honeywell became the first to commercially offer a quantum computer achieving a Quantum Volume of 64, with the launch of their System Model HØ. Following Honeywell’s announcement, we at QunaSys started thinking about what we could do with the world’s most powerful quantum computer? In cooperation with…

Subspace-Search Variational Quantum Eigensolver — Quantum chemistry aims to describe the behavior of atoms and molecules. Geometrical structures, molecular vibrational motions, chemical reaction dynamics, and photon absorption and emission are critical characteristics. A complete and accurate electronic structure is a prerequisite for obtaining that information accurately. This requirement brings up the Schrodinger equation, which governs…

“Nature isn’t classical, dammit, and if you want to make a simulation of nature, you’d better make it quantum mechanical, and by golly, it’s a wonderful problem because it doesn’t look so easy.” A famous description said by Richard Feynman in 1982 brings us a concept of building a quantum…