# Resonant Perturbation Theory of Decoherence and Relaxation of Quantum Bits

## TL;DR

This paper introduces a rigorous resonant perturbation theory to analyze decoherence and relaxation in multi-qubit quantum systems coupled to bosonic reservoirs, avoiding master equation approximations.

## Contribution

It provides a general, exact framework for understanding decoherence in complex quantum systems without relying on traditional approximations.

## Key findings

- Derives a representation of reduced dynamics valid for all times
- Applicable to a wide range of systems beyond solvable models
- Does not depend on master equation approximations

## Abstract

We describe our recent results on the resonant perturbation theory of decoherence and relaxation for quantum system with many qubits. The approach represents a rigorous analysis of the phenomenon of decoherence and relaxation for general $N$-level systems coupled to reservoirs of the bosonic fields. We derive a representation of the reduced dynamics valid for all times $t\geq 0$ and for small but fixed interaction strength. Our approach does not involve master equation approximations and applies to a wide variety of systems which are not explicitly solvable.