Quantumness of hybrid systems under quantum noise

TL;DR

This work analyzes quantum correlations in a $2x3$ axially symmetric qubit-qutrit system under thermal effects and local noise. It uses negativity for entanglement and linear-entropy-based quantum discord to capture both entangled and broader nonclassical correlations, comparing dephasing and phase-flip channels in symmetric and asymmetric decoherence. The results show entanglement decays with temperature and noise and can undergo entanglement sudden death, while discord persists beyond the entanglement threshold and can exhibit a low-temperature maximum; asymmetric noise enhances robustness of both measures, and phase-flip noise is more destructive than dephasing. Overall, the study offers insight into preserving quantum resources in hybrid spin systems and informs the design of robust quantum-information protocols for qubit-qutrit platforms.

Abstract

We investigate the quantum correlations in an axially symmetric hybrid qubit-qutrit system subjected to different noisy environments. We first introduce a physical model and analyze its Hamiltonian structure, emphasizing the role of hybrid dimensionality and axial symmetry. The effects of decoherence are then examined under two local noise mechanisms, namely dephasing and phase-flip channels, acting on the qubit and qutrit subsystems in both symmetric and asymmetric configurations. Quantum correlations are quantified using negativity to capture entanglement and quantum discord based on linear entropy to characterize more general nonclassical correlations. Our results show that both thermal fluctuations and phase noise lead to a monotonic degradation of quantum correlations, with increasing temperature accelerating coherence loss and inducing entanglement sudden death at finite temperatures. While negativity vanishes abruptly under sufficiently strong noise, quantum discord persists beyond the entanglement threshold, revealing residual quantum correlations in mixed states. We further demonstrate that asymmetric noise configurations significantly enhance the robustness of both entanglement and discord by partially shielding coherence in the less affected subsystem. A comparative analysis reveals that phase-flip noise is more destructive than pure dephasing, leading to faster suppression of quantum correlations.

Figures (2)

• Figure 1: Negativity as a function of temperature for the hybrid system under different noisy channels: (a) and (b) correspond to the dephasing channel, while (c) and (d) correspond to the phase-flip channel. Plots (a) and (c) correspond to $\gamma_A(t)=\gamma_B(t)=\gamma(t)$ and (b) and (d) correspond to $\gamma_B(t)=0$. Fixed parameters are: $J=0$, $J_z=1$, $K=0.2$, $K_1=-0.1$, $K_2=0.22$, $B_1=0.3$, $B_2=-0.7$, $D_z=0.32$, $\Gamma=-0.87$, and $\Lambda=0.31$.
• Figure 2: Similar to Fig. \ref{['Negativity in chan 1 and 2']} but for linear-entropy-based QD.