# Quantum Bayesian Networks

## May 28, 2016

### Don’t tell Microsoft. Qubiter, an open source platform, can now do quantum chemistry too

Filed under: Uncategorized — rrtucci @ 8:10 pm

https://github.com/rrtucci/my-chemistry

a small collection of classes called my-chemistry’ that allow one to construct a gate model quantum circuit for calculating the ground state energy of molecules using Kitaev’s Phase Estimation Algorithm.

Notice that I am releasing my-chemistry under my name only. Although this is an add-on to the artiste-qb.net Qubiter project, the Artiste company is free of any legal liability, as I have not merged it with the main code branch, and the company is not deriving any use of it at this time.

The docstrings of each class describe in detail how it works. All my classes have a main method at the end with examples and tests of the class. In addition, I have written a pdf document describing the more technical details of the quantum circuit involved. The pdf document is part of the my-chemistry distribution.

Here is an excerpt from the Introduction section of that pdf document:

This paper describes the particular circuit used by a Python software package called “my-chemistry”, written by R.R.Tucci, and available at GitHub, Ref.[1]. The software can be used in conjunction with “Qubiter”, another Python software package available at GitHub, Ref.[2].

A quantum circuit that is very similar to the one presented in this paper has previously been implemented FIRST in Ref.[4] and more recently and exhaustively in the closed source software package called Liqui$|\rangle$ produced by Microsoft, with Dave Wecker as main author.

Here is a super brief, by no means exhaustive review of some of the highlights in the history of this quantum computing approach to chemistry.

The person deserving the lion share of the credit for this method is A. Kitaev, who in 1995, Ref.[3], was the first to propose the PEA. Also very deserving are Trotter for his expansion, and Jordan/Wigner for their transformation.

The first paper to present an actual computer program for calculating the ground state energy of an $H_2$ molecule using PEA appears to be Ref.[4], by Whitfield, Biamonte and Aspuru-Guzik.

Researchers working for Microsoft applied the method to more complicated molecules and found some very clever optimization methods, such as using the identity $(CNOT)^2 = 1$. Here is their epiphany paper Ref.[5], and here is their most recent paper Ref.[6]. The latter is recommended for what appears to be a very fair and exhaustive list of references of this approach.

Finally, one should mention that Microsoft has several patents on this method, so it is possible that Microsoft will claim in the future that the software described in this paper infringes on one of their patents. Going to the USPTO website and using the query IN/wecker AND AN/Microsoft`, I located 4 patents Refs.[7][8][9][10] on Liqui$|\rangle$. There might be more pending.

Patents alluded to

Quantum gate optimizations