# System-Environment Correlations in Qubit Initialization and Control

## TL;DR

This paper investigates quantum correlations in superconducting qubits, revealing a fundamental speed-accuracy trade-off in initialization and providing insights for optimizing reset protocols and predicting gate fidelities.

## Contribution

It employs numerically exact methods to analyze system-reservoir correlations in transmon qubits, highlighting intrinsic constraints in qubit reset speed and accuracy.

## Key findings

- Identifies a speed-accuracy trade-off in qubit initialization.
- Shows standard models suffice for predicting gate fidelities.
- Provides a framework for experimental probing of qubit environments.

## Abstract

The impressive progress in fabricating and controlling superconducting devices for quantum information processing has reached a level where reliable theoretical predictions need to account for quantum correlations that are not captured by the conventional modeling of contemporary quantum computers. This applies particularly to the qubit initialization as the process which crucially limits typical operation times. Here we employ numerically exact methods to study realistic implementations of a transmon qubit embedded in electromagnetic environments focusing on the most important system-reservoir correlation effects such as the Lamb shift and entanglement. For the qubit initialization we find a fundamental trade-off between speed and accuracy which sets intrinsic constraints in the optimization of future reset protocols. Instead, the fidelities of quantum logic gates can be sufficiently accurately predicted by standard treatments. Our results can be used to accurately predict the performance of specific set-ups and also to guide future experiments in probing low-temperature properties of qubit reservoirs.