Introduction

HQS Bath Fitter is a tool of HQS Quantum Libraries by HQS Quantum Simulations GmbH to fit a given bath of an open quantum system with an effective bath derived from a set number of bath qubits. It provides a BathFitter Python class that includes several methods specifically for the system-bath analysis, as listed in the Features subsection below.

HQS Bath Fitter

Applications

HQS Bath Fitter is designed to implement complex open quantum systems by approximating their environmental interactions with effective baths. This tool is particularly useful in quantum algorithm development, noise modeling in quantum devices, simulations of open system dynamics, and optimizing the application of Trotterized time evolution in quantum computing. It enables researchers and engineers to translate physical noise environments into compact, efficiently simulatable models, and offers interoperability with other HQStage modules for end-to-end quantum simulation workflows.

A representative application is the fitting of an Ohmic spectral function when a spin system is coupled to an Ohmic bath. The case of an Ohmic bath arises in many areas of physics and highlights how the system-bath dynamics can drastically change depending on the system-bath coupling strength.

Another, more complex, application involves fitting a highly structured (peaked) target spectral function like it arises in noise environments containing so called two level systems — demonstrating the library’s flexibility in handling diverse modeling scenarios.

Interested readers may refer to Figures 2 and 5 in our publication for sample results from these applications.

Getting started

HQS Bath Fitter is a package of HQS Quantum Libraries that can be used in conjunction with other HQStage modules by HQS Quantum Simulations GmbH. To install this module run

hqstage install hqs-quantum-libraries

For a code snippet how to start using HQS Bath Fitter please refer to the usage section. For an expanded collection of examples please see the examples section.

Features

HQS Bath Fitter Library provides the following functions to finding an effective open system, i.e. expressing a target bath with helper qubits.

  1. fit_boson_bath_to_boson_bath
  2. fit_spin_bath_to_boson_bath
  3. fit_boson_bath_to_fermion_bath
  4. fit_spin_bath_to_fermion_bath
  5. fit_boson_bath_to_spectral_function
  6. fit_spin_bath_to_spectral_function
  7. spin_bath_trotterstep_from_boson_bath

For further information, the API documentation can be found here.

Further reading

The HQS Bath Fitter is based on our paper describing a quantum algorithm for solving open system dynamics on quantum computers using noise.