Home > Press > Quantum chemical calculations on quantum computers: A quantum algorithm capable of performing quantum circuits parallelism and full configuration interactions calculations in any open shell molecules without exponential/combinatorial explosion

(a) (left) Previously proposed quantum circuit. (b) (right) New parallelized quantum circuit. In (b), the complexity of the circuit is reduced drastically.
CREDIT
K. Sugisaki, T. Takui et al./Osaka City University |

**Abstract:**

Quantum computing and quantum information processing technology have attracted attention in recently emerging fields. Among many important and fundamental issues in nowadays science, solving Schroedinger Equation (SE) of atoms and molecules is one of the ultimate goals in chemistry, physics and their related fields. SE is "First Principle" of non-relativistic quantum mechanics, whose solutions termed wave-functions can afford any information of electrons within atoms and molecules, predicting their physicochemical properties and chemical reactions. Researchers from Osaka City University (OCU) in Japan, Dr. K. Sugisaki, Profs. K. Sato and T. Takui and coworkers have found a quantum algorithm enabling us to perform full configuration interaction (Full-CI) calculations for any open shell molecules without exponential/combinatorial explosion. Full-CI gives the exact numerical solutions of SE, which are one of the intractable problems with any supercomputers. The implementation of such a quantum algorithm contributes to the acceleration of implementing practical quantum computers.

The paper has been published on December 13th, 2018 in the first issue of Open Access Journal Chemical Physics Letters X.

They said, "As Dirac claimed in 1929 when quantum mechanics was established, the exact application of mathematical theories to solve SE leads to equations too complicated to be soluble [1]. In fact, the number of variables to be determined in the Full-CI method grows exponentially against the system size, and it easily runs into astronomical figures such as exponential explosion. For example, the dimension of the Full-CI calculation for benzene molecule C6H6, in which only 42 electrons are involved, amounts to 1044, which are impossible to be dealt with any supercomputers."

According to the OCU research group, quantum computers can date back to a Feynman's suggestion in 1982 that the quantum mechanics can be simulated by a computer itself built of quantum mechanical elements which obey quantum mechanical laws. After more than 20 years later, Prof. Aspuru-Guzik, Harvard Univ. (Toronto Univ. since 2018) and coworkers proposed a quantum algorithm capable of calculating the energies of atoms and molecules not exponentially but polynomially against the number of the variables of the systems, making a breakthrough in the field of quantum chemistry on quantum computers [2].

When Aspuru's quantum algorithm is applied to the Full-CI calculations on quantum computers, good approximate wave-functions close to the exact wave-functions of SE under study are required, otherwise bad wave-functions need an extreme number of steps of repeated calculations to reach the exact ones, hampering the advantages of quantum computing. This problem becomes extremely serious for any open shell systems, which have many unpaired electrons not participating in chemical bonding. The OCU researchers have tackled this problem, one of the most intractable issues in quantum science, and made a breakthrough in implementing a quantum algorithm generating particular wave-functions termed configuration state functions in polynomial computing time in 2016 [3].

The previously proposed algorithm requires a considerable number of quantum circuit gate operations proportional to the squares of the number of N, which denotes the number of down-spins of the unpaired electrons in the system. Thus, if N increases, the total computing time increases not exponentially but drastically. Additionally, the complexity of the quantum circuits should be reduced for practical usage of the algorithm and quantum programing architecture. A new quantum algorithm exploits germinal spin functions, termed Serber construction, and reduces the number of the gate operations to only 2N, executing parallelism of the quantum gates. The OCU group said, "This is the first example of practical quantum algorithms, which make quantum chemical calculations realizable on quantum computers equipped with a sizable number of qubits. These implementations empower practical applications of quantum chemical calculations on quantum computers in many important fields."

###

[1] P.A.M. Dirac, Quantum mechanics of many-electron systems. Proc. R. Soc. London, Ser. A 1929, 123, 714-733.

[2] A. Aspuru-Guzik, A. D. Dutoi, P. J. Love, M. Head-Gordon, Science 2005, 309, 1704.

[3] K. Sugisaki, S. Yamamoto, S. Nakazawa, K. Toyota, K. Sato, D. Shiomi, T. Takui, J. Phys. Chem. A 2016, 120, 6459-6466. DOI: 10.1021/acs.jpca.6b04932

####

**For more information, please click here**

**Contacts:**

Takeji Takui

81-666-055-034

Copyright © Osaka City University

If you have a comment, please Contact us.Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Related Links |

Related News Press |

**News and information**

New method to reduce uranium concentration in contaminated water March 18th, 2019

Review of the recent advances of 2D nanomaterials in Lit-ion batteries March 15th, 2019

**Chemistry**

**Possible Futures**

New method to reduce uranium concentration in contaminated water March 18th, 2019

Review of the recent advances of 2D nanomaterials in Lit-ion batteries March 15th, 2019

**Quantum Computing**

Researchers reverse the flow of time on IBM's quantum computer March 14th, 2019

Researchers move closer to practical photonic quantum computing: New method fills critical need to measure large-scale quantum correlation of single photons February 28th, 2019

Media invited to open meeting on the future of quantum technology held at RIT Jan. 23-25: Leaders from NASA, NSF, NIST and Sandia National Laboratory to attend January 11th, 2019

Spintronics 'miracle material' put to the test: Physicists build devices using mineral perovskite January 11th, 2019

**Discoveries**

New method to reduce uranium concentration in contaminated water March 18th, 2019

Review of the recent advances of 2D nanomaterials in Lit-ion batteries March 15th, 2019

**Announcements**

New method to reduce uranium concentration in contaminated water March 18th, 2019

Review of the recent advances of 2D nanomaterials in Lit-ion batteries March 15th, 2019

**Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers**

New method to reduce uranium concentration in contaminated water March 18th, 2019

Review of the recent advances of 2D nanomaterials in Lit-ion batteries March 15th, 2019

**Grants/Sponsored Research/Awards/Scholarships/Gifts/Contests/Honors/Records**

Researchers reverse the flow of time on IBM's quantum computer March 14th, 2019

Pushing Past Limits: Junkai Jiang receives prestigious Ph.D. Student Fellowship from IEEE Electron Devices Society March 14th, 2019

The latest news from around the world, FREE | ||

Premium Products |
||

Only the news you want to read!
Learn More |
||

Full-service, expert consulting
Learn More |
||