Distortion of a reduced equilibrium density matrix: influence on quantum emulation

TL;DR

This paper analyzes how external bosonic environments distort the equilibrium state of a quantum system, impacting the reliability of quantum emulators by showing how bath interactions modify system energies and eigenstates.

Contribution

It introduces a general framework for understanding how system-bath coupling affects the reduced density matrix in quantum emulators, highlighting the impact of external degrees of freedom.

Findings

External bosonic modes cause energy renormalization.

System eigenbasis is altered by bath interactions.

Implications for the reliability of quantum emulators.

Abstract

We study a system coupled to external degrees of freedom, called bath, where we assume that the total system, consisting of system and bath is in equilibrium. An expansion in the coupling between system and bath leads to a general form of the reduced density matrix of the system as a function of the bath selfenergy. The coupling to the bath results in a renormalization of the energies of the system and in a change of the eigenbasis. This theory is applicable to quantum emulators in thermal equilibrium. Undesired external degrees of freedom can affect their reliability. We study the influence of bosonic degrees of freedom on the state of a six qubit system.