# Quantumness and memory of one qubit in a dissipative cavity under classical control

## TL;DR

This paper investigates how classical control influences quantum properties and memory effects in a qubit within a dissipative cavity, revealing conditions that enhance quantumness and preserve geometric phase.

## Contribution

It provides a detailed analysis of the interplay between classical control, non-Markovianity, and quantum features in a qubit-cavity system, highlighting new ways to preserve quantum coherence.

## Key findings

- Stronger classical coupling enhances quantumness despite reduced non-Markovianity.
- Increasing qubit-field detuning diminishes nonclassicality but restores non-Markovian effects.
- Strong classical control can preserve the qubit's geometric phase regardless of cavity spectral width.

## Abstract

Hybrid quantum-classical systems constitute a promising architecture for useful control strategies of quantum systems by means of a classical device. Here we provide a comprehensive study of the dynamics of various manifestations of quantumness with memory effects, identified by non-Markovianity, for a qubit controlled by a classical field and embedded in a leaky cavity. We consider both Leggett-Garg inequality and quantum witness as experimentally-friendly indicators of quantumness, also studying the geometric phase of the evolved (noisy) quantum state. We show that, under resonant qubit-classical field interaction, a stronger coupling to the classical control leads to enhancement of quantumness despite a disappearance of non-Markovianity. Differently, increasing the qubit-field detuning (out-of-resonance) reduces the nonclassical behavior of the qubit while recovering non-Markovian features. We then find that the qubit geometric phase can be remarkably preserved irrespective of the cavity spectral width via strong coupling to the classical field. The controllable interaction with the classical field inhibits the effective time-dependent decay rate of the open qubit. These results supply practical insights towards a classical harnessing of quantum properties in a quantum information scenario.