Operational approach to open dynamics and quantifying initial correlations

TL;DR

This paper introduces a quantum process tomography method that accurately describes the dynamics of a system even when initial correlations with the environment are present, and also quantifies these initial correlations.

Contribution

It provides a novel quantum process tomography approach that accounts for initial system-environment correlations, extending the standard method which assumes independence.

Findings

Method accurately describes dynamics with initial correlations

Quantitative expressions for initial correlations are derived

Applicable to various physical systems with correlated initial states

Abstract

A central aim of physics is to describe the dynamics of physical systems. Schrodinger's equation does this for isolated quantum systems. Describing the time evolution of a quantum system that interacts with its environment, in its most general form, has proved to be difficult because the dynamics is dependent on the state of the environment and the correlations with it. For discrete processes, such as quantum gates or chemical reactions, quantum process tomography provides the complete description of the dynamics, provided that the initial states of the system and the environment are independent of each other. However, many physical systems are correlated with the environment at the beginning of the experiment. Here, we give a prescription of quantum process tomography that yields the complete description of the dynamics of the system even when the initial correlations are present. Surprisingly, our method also gives quantitative expressions for the initial correlation.