Inferring Markovian quantum master equations of few-body observables in interacting spin chains

TL;DR

This paper introduces a machine learning-based variational approach to infer physically consistent Markovian quantum master equations for local observables in interacting spin chains, enabling better understanding of subsystem dynamics.

Contribution

It develops a novel variational method to learn Lindblad generators from quantum data, ensuring physical consistency and applicability to complex many-body systems.

Findings

Successfully recovers two-body subsystem dynamics.

Predicts stationary states of the subsystem.

Demonstrates physical consistency of learned generators.

Abstract

Full information about a many-body quantum system is usually out-of-reach due to the exponential growth -- with the size of the system -- of the number of parameters needed to encode its state. Nonetheless, in order to understand the complex phenomenology that can be observed in these systems, it is often sufficient to consider dynamical or stationary properties of local observables or, at most, of few-body correlation functions. These quantities are typically studied by singling out a specific subsystem of interest and regarding the remainder of the many-body system as an effective bath. In the simplest scenario, the subsystem dynamics, which is in fact an open quantum dynamics, can be approximated through Markovian quantum master equations. Here, we formulate the problem of finding the generator of the subsystem dynamics as a variational problem, which we solve using the standard toolbox of machine learning for optimization. This dynamical or ``Lindblad" generator provides the relevant dynamical parameters for the subsystem of interest. Importantly, the algorithm we develop is constructed such that the learned generator implements a physically consistent open quantum time-evolution. We exploit this to learn the generator of the dynamics of a subsystem of a many-body system subject to a unitary quantum dynamics. We explore the capability of our method to recover the time-evolution of a two-body subsystem and exploit the physical consistency of the generator to make predictions on the stationary state of the subsystem dynamics.