Spin clean-up method brings practical quantum computers closer to
reality

Date:
September 25, 2020
Source:
Osaka City University
Summary:
Researchers create a quantum algorithm that removes spin
contaminants while making chemical calculations on quantum
computers. This allows for predictions of electronic and molecular
behavior with degrees of precision not achievable with classical
computers and paves the way for practical quantum computers to
become a reality.



FULL STORY ========================================================================== Quantum computers are the new frontier in advanced research technology,
with potential applications such as performing critical calculations, protecting financial assets, or predicting molecular behavior in pharmaceuticals.

Researchers from Osaka City University have now solved a major problem hindering large-scale quantum computers from practical use: precise and accurate predictions of atomic and molecular behavior.


==========================================================================
They published their method to remove extraneous information from
quantum chemical calculations on Sept. 17 as an advanced online article
in Physical Chemistry Chemical Physics, a journal of the Royal Society
of Chemistry.

"One of the most anticipated applications of quantum computers is
electronic structure simulations of atoms and molecules," said paper
authors Kenji Sugisaki, Lecturer and Takeji Takui, Professor Emeritus
in the Department of Chemistry and Molecular Materials Science in Osaka
City University's Graduate School of Science.

Quantum chemical calculations are ubiquitous across scientific
disciplines, including pharmaceutical therapy development and materials research. All of the calculations are based on solving physicist
Erwin Schro"dinger's equation, which uses electronic and molecular
interactions that result in a particular property to describe the state
of a quantum-mechanical system.

"Schro"dinger equations govern any behavior of electrons in molecules, including all chemical properties of molecules and materials, including chemical reactions," Sugisaki and Takui said.

On classical computers, such precise equations would take exponential
time. On quantum computers, this precision is possible in realistic time,
but it requires "cleaning" during the calculations to obtain the true
nature of the system, according to them.

A quantum system at a specific moment in time, known as a wave function,
has a property described as spin, which is the total of the spin of each electron in the system. Due to hardware faults or mathematical errors,
there may be incorrect spins informing the system's spin calculation. To
remove these 'spin contaminants,' the researchers implemented an algorithm
that allows them to select the desired spin quantum number. This purifies
the spin, removing contaminants during each calculation -- a first on
quantum computers, according to them.

"Quantum chemical calculations based on exactly solving Schro"dinger
equations for any behavior of atoms and molecules can afford predictions
of their physical-chemical properties and complete interpretations on
chemical reactions and processes," they said, noting that this is not
possible with currently available classical computers and algorithms. "The present paper has given a solution by implementing a quantum algorithm on quantum computers." The researchers next plan to develop and implement algorithms designed to determine the state of electrons in molecules
with the same accuracy for both excited- or ground-state electrons.


========================================================================== Story Source: Materials provided by Osaka_City_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Kenji Sugisaki, Kazuo Toyota, Kazunobu Sato, Daisuke Shiomi, Takeji
Takui. A probabilistic spin annihilation method for quantum
chemical calculations on quantum computers. Physical Chemistry
Chemical Physics, 2020; DOI: 10.1039/d0cp03745a ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200925113349.htm

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