Charged Complexity and the Thermofield Double State

TL;DR

This paper develops a framework to analyze the quantum complexity of charged Gaussian states, especially the charged thermofield double state, revealing how chemical potential influences complexity dynamics and relating it to uncharged states.

Contribution

It introduces a systematic geometric approach to study complexity in charged systems and applies it to analyze the charged thermofield double state with chemical potential.

Findings

Complexity factorizes between charged modes.

Complexity relates to uncharged states with shifted parameters.

Numerical and analytic results show the impact of charge and chemical potential.

Abstract

We establish a systematic framework for studying quantum computational complexity of Gaussian states of charged systems based on Nielsen's geometric approach. We use this framework to examine the effect of a chemical potential on the dynamics of complexity. As an example, we consider the complexity of a charged thermofield double state constructed from two free massive complex scalar fields in the presence of a chemical potential. We show that this state factorizes between positively and negatively charged modes and demonstrate that this fact can be used to relate it, for each momentum mode separately, to two uncharged thermofield double states with shifted temperatures and times. We evaluate the complexity of formation for the charged thermofield double state, both numerically and in certain analytic expansions. We further present numerical results for the time dependence of complexity. We compare various aspects of these results to those obtained in holography for charged black holes.