QSCI - Quantum Selected Configuration Interaction¶

Welcome to the comprehensive documentation for QSCI (Quantum Selected Configuration Interaction) and TE-QSCI (Time-Evolved QSCI) algorithms implemented using the QURI ecosystem.

What is QSCI?¶

QSCI is a quantum algorithm for quantum chemistry that leverages time evolution to systematically explore electronic configurations without requiring variational optimization. This implementation provides multiple algorithm variants optimized for different use cases and quantum hardware architectures.

Key Features¶

Multiple Algorithm Variants: VanillaQSCI, SingleTimeTE_QSCI, TimeAverageTE_QSCI, and StateVectorTE_QSCI
QURI Ecosystem Integration: Full compatibility with QURI Parts, QURI Algo, and QURI VM
Time Evolution Methods: Support for both Trotter decomposition and exact unitary evolution
Quantum Hardware Analysis: Powered by QURI-VM , it supports circuit resource estimation for different quantum architectures, including ideal quantum circuit and FTQC devices

Algorithm Variants¶

VanillaQSCI¶

Standard QSCI algorithm using computational basis state sampling from quantum circuits.

SingleTimeTE_QSCI¶

Time-evolved QSCI at a single evolution time point for systematic configuration exploration.

TimeAverageTE_QSCI¶

Time-evolved QSCI averaged over multiple evolution times to improve sampling diversity.

StateVectorTE_QSCI¶

Time-evolved QSCI with direct state vector calculation for exact simulation studies.

Scientific Background¶

TE-QSCI generates important electronic configurations through time evolution:

\[|\psi(t)\rangle = e^{-i\hat{H}t}|\psi_I\rangle = |\psi_I\rangle - i\hat{H}t|\psi_I\rangle + \frac{(-i\hat{H}t)^2}{2!}|\psi_I\rangle + \ldots\]

Where the \(k\)-th order term includes up to \(2k\)-th order excitations, systematically exploring the configuration space needed for accurate quantum chemistry calculations.

Getting Started¶

Installation Guide - Set up QSCI with all dependencies
Quick Start - Run your first QSCI calculation
Algorithm Overview - Understand the different QSCI variants
Examples - Learn from practical examples

API Reference¶

Explore the complete API documentation:

Core Algorithms - VanillaQSCI, TimeEvolvedQSCI, and variants
Algorithm Interfaces - QURI-algo compatible interfaces
VM Analysis - Circuit analysis and resource estimation

Contributing¶

We welcome contributions! Please see our Contributing Guide for details on:

Adding new QSCI variants
Extending the testing framework
Improving documentation
Reporting issues

Citation¶

If you use QSCI in your research, please cite:

@article{Kanno:2023rfr,
    author = "Kanno, Keita and Kohda, Masaya and Imai, Ryosuke and Koh, Sho and Mitarai, Kosuke and Mizukami, Wataru and Nakagawa, Yuya O.",
    title = "{Quantum-Selected Configuration Interaction: classical diagonalization of Hamiltonians in subspaces selected by quantum computers}",
    eprint = "2302.11320",
    archivePrefix = "arXiv",
    primaryClass = "quant-ph",
    month = "2",
    year = "2023"
}

@article{Mikkelsen:2024onz,
    author = "Mikkelsen, Mathias and Nakagawa, Yuya O.",
    title = "{Quantum-selected configuration interaction with time-evolved state}",
    eprint = "2412.13839",
    archivePrefix = "arXiv",
    primaryClass = "quant-ph",
    month = "12",
    year = "2024"
}

License¶

This project is licensed under the MIT License - see the License file for details.