ACE: A general-purpose non-Markovian open quantum systems simulation toolkit based on process tensors

TL;DR

This paper introduces ACE, a versatile computational toolkit that uses process tensor matrix product operators to simulate complex non-Markovian open quantum systems with high efficiency and accuracy.

Contribution

The paper presents a novel, general-purpose toolkit based on process tensor matrix product operators for simulating non-Markovian open quantum systems, including new algorithms and efficient simulation schemes.

Findings

Enables million time step simulations of realistic models.

Provides reusable PT-MPOs for different Hamiltonians.

Supports small quantum network solutions.

Abstract

We describe a general-purpose computational toolkit for simulating open quantum systems, which provides numerically exact solutions for composites of zero-dimensional quantum systems that may be strongly coupled to multiple, quite general non-Markovian environments. It is based on process tensor matrix product operators (PT-MPOs), which efficiently encapsulate environment influences. The code features implementations of several PT-MPO algorithms, in particular, Automated Compression of Environments (ACE) for general environments comprised of independent modes as well as schemes for generalized spin boson models. The latter includes a divide-and-conquer scheme for periodic PT-MPOs, which enable million time step simulations for realistic models. PT-MPOs can be precalculated and reused for efficiently probing different time-dependent system Hamiltonians. They can also be stacked together and combined to provide numerically complete solutions of small networks of open quantum systems. The code is written in C++ and is fully controllable by configuration files, for which we have developed a versatile and compact human-readable format.