HQS Qorrelator App User Guide
The HQS Qorrelator App is designed to provide users with a simple tool to perform the calculation of correlation functions on a quantum computer. Correlation functions are important for many areas of physics and chemistry. One of the most commercially important aspects is that correlation functions can be used to calculate response spectra. Specifically, correlation functions of two spin operators, with respect to the Hamiltonian of the nuclear material, can be used to obtain the NMR spectral function. Due to the enormous practical relevance of NMR spectra, the first version of the HQS Qorrelator App focuses on providing ways to obtain the NMR correlation functions on a quantum computer.
In the near future, all available quantum computers will be NISQ quantum computers, where the qubits of the quantum computer experience environmental noise. In most applications, environmental noise is purely a source of errors. At HQS, we have realised that, for certain applications, environmental noise is not detrimental and can even be used as an computational resource.
The HQS Qorrelator App also incorporates these approaches in an user-friendly manner, by providing an easy way to obtain an estimate of the spectral broadening due to the effective time evolution that occurs on a noisy quantum computer.
Fundamental Physical concepts
Background
In this chapter we provide background knowledge on the basics of nuclear magnetic resonance (NMR) from experimental and theoretical perspectives. We also describe the maths behind the calculation of spectra in the HQS Qorrelator App. Lastly, we explain how quantum computers can be used to calculate NMR spectra.
Noise models
We consider physical noise, meaning noise on the hardware-level, that is caused by qubits coupling to some fluctuating environment, either during control operations, or at all times. This is assumed to cause damping, dephasing, and/or depolarization of their quantum states. Our model of a noisy quantum computer is based on adding corresponding non-unitary (noise) operations after or before (ideal) unitary gate operations. This model is described in detail on page modeling.
Noise mapping
The HQS Qorrelator App allows the user to investigate how noise affects the calculation of correlation functions to obtain NMR spectra. Particularly, it derives the Lindblad open-system model that the noisy quantum simulator is effectively implementing in the time propagation that is part of the calculation of the correlation function. Foundations of this mapping (between physical and simulated noise) are discussed on page mapping or in more detail in this arxiv paper.
Using the program
On the interface page, we go through the Python interface of the HQS Qorrelator App package and discuss how to construct quantum programs that will calculate correlations, how to get an estimated broadening based on the noise in a device and how to extract the noisy algorithm model.
API Documentations
Changelog
For a changelog starting from version 0.2 please see here.