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Published Articles


Quantum Circuits for Collective Amplitude Damping in Two-Qubit Systems

Yusuke Hama

The biggest difficulty in performing quantum computation is that the qubit system that constitutes the quantum computer hardware changes its qubit state due to noise from the environment. We formulated a quantum circuit against quantum noise.


Implementation of quantum imaginary-time evolution method on NISQ devices by introducing nonlocal approximation

Hirofumi Nishi, Taichi Kosugi, and Yu-ichiro Matsushita, npj Quantum Information 7, 85 / 1-7 (2021).

An effective quantum algorithm (quantum imaginary time evolution method) for material calculation and optimization problems has been proposed for the implementation of NISQ (Noisy Intermediate-Scale Quantum) devices, and the paper has been published.
NISQ devices, which are expected to be realized in the near future, have a limited number of quantum operations due to the lack of error correction. In this research, we have succeeded in developing an effective quantum algorithm for material calculation and optimization problems that can be realized on NISQ devices.


Predicting toxicity by quantum machine learning

Teppei Suzuki and Michio Katouda, Journal of Physics Communications 4, 125012 / 1-15 (2020).

We conducted research on the development of quantum computer applications for drug discovery research, and developed a quantum machine learning model for nonlinear regression on chemical data. Specifically, we developed a quantum machine learning model to predict the toxicity value of phenolic compounds based on quantitative structure-activity relationships.


Linear-response functions of molecules on a quantum computer: Charge and spin responses and optical absorption

Taichi Kosugi and Yu-ichiro Matsushita, Physical Review Research 2, 033043/1-16 (2020).

We proposed a general circuit construction method to implement non-unitary operators as a combination of unitary operators and measurements, and used it to simulate quantum chemical calculations of linear response functions such as optical absorption spectra of molecules. The second quantized operators required for the calculation of physical quantities were implemented by the mayoranization and ancillar bit of the electron creation and annihilation operators. Our method can be applied not only to quantum chemistry but also to quantum algorithms in various fields, and is expected to become a fundamental technology for the full-scale implementation phase of quantum computation.


Construction of Green's functions on a quantum computer: applications to molecular systems

Taichi Kosugi and Yu-ichiro Matsushita, Physical Review A 101, 012330 / 1-12 (2020).

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