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arXiv · 2509.12717

Ancilla-train quantum algorithm for simulating non-Markovian open quantum systems

Hans Michael Christensen·Johannes Agerskov·Frederik Nathan
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Abstract

We present a quantum algorithm for simulating open quantum systems coupled to Gaussian environments valid for any configuration and coupling strength. The algorithm is applicable to problems with strongly coupled, or non-Markovian, environments, problems with multiple environments out of mutual equilibrium, and problems with time-dependent Hamiltonians. We show that the algorithm can reproduce the true dynamics of such problems at arbitrary accuracy and, for a broad range of problems, only adds a minor resource cost relative to Trotterized time evolution; the cost is low-degree polynomial in the inverse target accuracy. The algorithm is based on the insight that any Gaussian environment can be represented as a train of ancillary qubits that sequentially interact with the system through a time-local coupling, given by the convolution square root of the bath correlation function; this is a secondary result of our work. Our results open up new applications of quantum computers for efficient simulation of non-equilibrium and open quantum systems.

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Hans Michael Christensen, Johannes Agerskov, Frederik Nathan. 2025-09-16. Ancilla-train quantum algorithm for simulating non-Markovian open quantum systems. https://arxiv.org/abs/2509.12717

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